Hi All,

I responded to a Facebook Marketplace ad for an RCA CT-100 near Windsor Ontario for sale for just C$10 (US$7.80). I messaged the seller and told him the history and said it was the first color tv from 1954 and it was too cheap. He said okay. How about C$100? I texted back sure lol!

So I made a 3 hour drive to arrive at the gentleman's doorstep at 8am the next morning. It is unusually cold for this time of year and the temperature was -5 Celcius (29F). The set was in the open and had sat for a couple of days at least outside. Fortunately there had been no rain.

I honestly thought the ad may be a sham but I was game to drive and have a look. It was indeed a CT100 and is as depicted below. The gentleman told me he susequently received a flood of calls telling him. the set was worth $1500. But his residence was flooded with tons of old electronic stuff and I asked him directly if the C$100 was okay and he said sure as long as I haul it away.

The set came from an estate near Windsor Ontario. I could see sometime ago some work had been done with quite a number of orange drop Sprague capacitor replacements evident. The is mouse nest damage in a corner of the chassis because the bottom chassis plate was missing. The speaker frame also suffered considerable rusting from what appeared due to mouse urine. But the set otherwise was in fairly reasonable complete state apart from the missing chassis bottom screen, the knobs and the back cover.

On site I carefully dismantled the cabinet and removed the chassis and 15GP22. On it's ride back hope, the CRT was carefully cushioned on the rear seat of my car. A cursory glance shows no white round the getters and it still looks like there is a good vacuum. I plan to bring out my CRT tester and carefully scrutinize the status of the CRT.

For you information, the chassis number is B8001599, cabinet 170. I am in the process of revising my plans this summer to include time to begin resusitating this set. This will be particularly so if the CRT shows any sign of life. I shall use this thread to maintain a running discussion.

You lucky dog! Fingers crossed on the CRT.

Nice! Haven't seen one of thee pop up in a while!

I also hope the CRT in your new (to you) CT-100 is good, and the TV itself works well, considering its age. However, I would not expect the set to work "like new", considering it was built in 1954. You will almost certainly have to replace tubes and perhaps rotted wiring under the chassis, not to mention doing a full reconvergence of the color CRT. I would not even think of plugging the set into an AC outlet and turning it on before the set has been thoroughly tested. As I am about to explain, this television is extremely rare and probably has the proverbial "million and one" things wrong with it, such as bad tubes, defective capacitors (especially power supply filter caps), off-tolerance resistors, and other things too numerous to mention.

The CT-100 is a very rare TV, as it was one of the first (if not in fact the first) mass-produced color sets, very likely with a very steep price tag as well. My guess is very few people owned one of these unless they were rich, had won the lottery, or had inherited a fortune (before taxes, of course) from a deceased relative.

There weren't that many TV stations in the United States broadcasting color programming when this TV was new, so the chances are most of the programming seen on these sets was broadcast in b&w, with the occasional (I stress the word occasional) color program in prime time.

Most network news broadcasts of the 1950s were shown in b&w, with the exception of NBC's nightly news which was always broadcast in, as that network always put it, living color. NBC was America's "full color" television network, and of course they made a big point of that every chance they had. "The following program is brought to you in living color on NBC" was always announced before every color show on the network, with a full-color peacock spreading its feathers during the announcement.

BTW, I would guess anyone who saw the NBC peacock in b&w (given the steep price of color television sets in the '50s, most homes with TV had only one b&w TV in the living room) wished they had a color TV. However, most viewers did see the bird in black and white until color sets became affordable. No doubt most American living rooms with color TV were showplaces during the 1950s through the eighties, as most folks, as I said, could not afford the first color televisions; those who did have a color set probably guarded the set as if it were made of gold, and did not allow children anywhere near it unless an adult was present.

Wish you the very best in the restoration of this set. Hope the CRT is okay.

Other than bad caps and perhaps the selenium rectifiers and some green rectangular power resistors, and ... the worst ... the white (not brown) peaking coils in the video, these things are uisually in pretty good shape.
Mine really had only one nasty problem area, the horizontal sync was intermittent. It was fixed only by replacing each and every resistor in the horizontal sync and oscillator.

On the other hand, the alignment was horrible. I very carefully counted and there are 81 adjustments (counting only one channel in the tuner) That includes the yoke tilts.

Good luck!

I've been around the back of color TV's for the better part of 40 years and had never seen the CTC-100, was this a unique CRT? I'm not seeing the customary convergence or triad gun layout so I'm somewhat puzzled on this one.

I've been around the back of color TV's for the better part of 40 years and had never seen the CTC-100, was this a unique CRT? I'm not seeing the customary convergence or triad gun layout so I'm somewhat puzzled on this one.

The 15GP22, Its advanced phosphor deposition CBS equivalent the 15HP22, and the much rarer 19" version (19VP22?)...All used electrostatic dynamic convergence (something like 6KV DC with 3KV AC riding on it) instead of the electromagnetic dynamic convergence the 21AXP22 and all later color tubes used until inline gun tubes eliminated dynamic convergence.

There's 3 adjustment screw magnets on purity coil* that are used for static convergence the same as later tubes.

*Instead of degaussing these tubes use a field neutralizing coil on the face and a purity coil on the neck....As a working CT-100 owner it took a little bit wrapping my head around how the adjustments work (and they're still not perfect thanks to a bent shadow mask), but it wasn't hard making them pretty good. There's less to a 15G convergence procedure than most later sets...only problem is HV tends to bloom and fluctuate (especially given I don't have enough high VA voltage regulating line isolation transformers to run my CT-100 off of)and the user pots for focus and occasionally convergence DC have to be tweaked to keep things looking good.
If I had enough room to put my CT-100 and 21CT55 in the same room I could make them share the transformer that feeds the 21CT55.

The 15GP22, Its advanced phosphor deposition CBS equivalent the 15HP22, and the much rarer 19" version (19VP22?)...All used electrostatic dynamic convergence (something like 6KV DC with 3KV AC riding on it) instead of the electromagnetic dynamic convergence the 21AXP22 and all later color tubes used until inline gun tubes eliminated dynamic convergence.

There's 3 adjustment screw magnets on purity coil* that are used for static convergence the same as later tubes.

*Instead of degaussing these tubes use a field neutralizing coil on the face and a purity coil on the neck....As a working CT-100 owner it took a little bit wrapping my head around how the adjustments work (and they're still not perfect thanks to a bent shadow mask), but it wasn't hard making them pretty good. There's less to a 15G convergence procedure than most later sets...only problem is HV tends to bloom and fluctuate (especially given I don't have enough high VA voltage regulating line isolation transformers to run my CT-100 off of)and the user pots for focus and occasionally convergence DC have to be tweaked to keep things looking good.
If I had enough room to put my CT-100 and 21CT55 in the same room I could make them share the transformer that feeds the 21CT55.

Actually the convergence for the CT-100 is a real chore. The reason is that
the tilt and centering of the deflection yoke is super critical. Its more critical for convergence than for purity. The good news is that essentially perfect
convergence is possible. The only reason my set does not have perfect convergence over the whole screen is a bit of ringing in the horizantal sweep.
This makes one vertical line in the crosshatch pattern be off in the blue.
Across the rest of the screen all lines are within 1/2 linewidth of perfect,
and most really are perfect.

In preparation for work on color sets at the ETF next week I checked my own CT-100 last night. In addition to convergence, in a dark room the color rendition is truly perfect, using both my own patterns and "Digital Video Essentials". On the usual "blue bars" matching test, and the equivalents for red and green on my own test patterns, all three colors are perfect.
This was only achieved by tweeking one of the matrix resistors long ago ...
its not needed changing since.

As I have said before ... if the cameras were tweeked as well as the (Model 5) sets for the demo for the FCC, everybody must have been stupefied by the quality. The I-Q system really does the job. I consider the ideal viewing distance for the CT-100 to be three feet! I routinely watch football, golf, and baseball on mine.
the viewers of the

This evening was the moment of truth: initial test of the 15GP22

I have a BK467 and a Sencore CR-70 CRT testers. I chose the CR-70 as it has the universal leads and the BK-467 hasn't the 20 pin CRT socket connector.

The 15GP22 appeared to light properly. It also looks as if the original 15GP22 socket was damaged and the previous keeper made an epoxy mold to fix it. Seems a satifactory fix and it is translucent which allows the filament glow to pass.

As I indicated earlier, I could not see any trace of white around the getter which offered hope the tube still had a vacuum. My initial setup to test did not allow me to set cutoff on the 15GP22. I decided to try testing a known good 10BP4 with the same negative result. I searched back on this forum to find any information and one post revealed adjusting the the cutoff, the G2 voltage should swing between 20 and 400 volts. I have not been able to find a schematic or any service data on the CR-70 and so took the CR-70 apart to find what was the matter. It appears one of the connectors was loose and reseating it got it working. I was able to test the 10BP4 now with success.

Back to the 15GP22, I set up the Sencore on first the RED gun, then Green and finally Blue. I was able to swing the cutoff adjustment for the needle in the box. Importantly the Cutoff adjustment swing was smooth from minimum to about mid scale deflection without any sudden jumps. I have read sudden jumps adjusting cutoff may imply ionization due to gas. Testing emission, the needle reached a respectible good on RED, GREEN and BLUE as depicted below. It looks like I may be lucky.

The pictures below depict:
1) RED Cutoff
2) RED Emission
3) GREEN Emission
4) BLUE Emission
5) Tube neck glow

So the chassis restore is next. I have read a lot on this forum about the 15GP22 and the use of Vacseal or its equivalent. This poor tube appears to have suffered in storage over the years and would appreciate opinions on the tube preservation.

Hopeful results.

What great news! Looking forward to more on the restoration.

Great - onward!

Wonderful! This is starting out as one of the best CT-100 stories.

Excellent news.

Great results it appears in the tester. I have a question about the background of your photo on the shelf. Are those 78 records? I can make out Rachmaninoff on the back of the spine on one of them.

Great results it appears in the tester. I have a question about the background of your photo on the shelf. Are those 78 records? I can make out Rachmaninoff on the back of the spine on one of them.

Yes I am an inveterate 78 collector. The Rachmaninoff is the 1929 recording with Stokowski and the Philadelphia Orchestra and Sergei Rachmaninoff at the piano.

"Rachmaninoff Plays Piano Concerto No 2 (1929)" on YouTube
https://youtu.be/X_7O09ucelM

With the 15GP22 showing life and promise, I am now proceeding to the chassis.

It is filthy although relatively complete. The selenium rectifier shield is missing along with the back cover and four knobs. The cabinet is in surprisingly good shape apart from the speaker rust. (I plan to dismantle the original speaker and derust via electrolysis).

But the main concern is first to clean up the chassis and remove a fair bit of corrosion from the mouse home. It is pretty extensive in the corner next to the first Video IF but not irreparible.

I noticed that the front part of the chassis contains almost all the corrosion. I see that the corroded front section is attached to the rest of the chassis with self tapping screws. So I plan to begin carefully documenting and photographing the wiring crossing the chassis bridge and separate the chassis away to attend to the localized rust.

I have photographed the front chassis attached to the main chassis below.

If you need the large roundie socket I have an extra one for the B&K 467.

Thanks for the tip. I have a box of BK467 sockets I will look thru.

I found an old label attached to the CRT leads.

The label reads Judd Electronic and the address is 16931 Schoolcraft.

I Googled Judd Electronic and nothing. I did find on Google Maps a Schoolcraft Road from just across the Canada US border where the set was found. Looks as if it was an early Detroit color tv.

You will see the label below, a Google map shwing a red dot to the right where I picked up the set and the Google Maps flag where 16931 Schoolcraft Road is. And finally the empty building where once stood Judd Electronic.

I found an old label attached to the CRT leads.

The label reads Judd Electronic and the address is 16931 Schoolcraft.

I Googled Judd Electronic and nothing. I did find on Google Maps a Schoolcraft Road from just across the Canada US border where the set was found. Looks as if it was an early Detroit color tv.

You will see the label below, a Google map shwing a red dot to the right where I picked up the set and the Google Maps flag where 16931 Schoolcraft Road is. And finally the empty building where once stood Judd Electronic.

I believe (and don't quote me on this as roads in Michigan and Indiana use very different naming conventions) that the name "Schoolcraft Road" refers to the fact that if you follow the road long enough it will eventually take you to a Village called Schoolcraft, Michigan (which is between Three Rivers and Kalamazoo, Michigan on US 131 N.)

But like I said I don't know if that's why that road was named that or not, because like I said, in Indiana a road that was named after a nearby town was named that because that road would eventually take you to that town if you followed it long enough, which like I said I don't know if Michigan followed that rule or not when naming their roads.

Just my two wheat pennies worth.

Interesting story about Schoolcraft Road. I will study the map!

Yesterday dismantled the rusty loudspeaker and put the frame into an electrolysis bath. Painted the frame silver this morning and will wait a couple of weeks before reassembling. Spent last night and this evening documenting and photographing the front chassis section which suffered from the mice next. I have removed the front chassis and have begun dismantling it. Fortunateltly pretty weel all the rust is around the first video IF stage and the audio amplifier. I shall concentrate cleaning this section up before proceeding to the rest of the chassis.

Yes I am an inveterate 78 collector. The Rachmaninoff is the 1929 recording with Stokowski and the Philadelphia Orchestra and Sergei Rachmaninoff at the piano.

"Rachmaninoff Plays Piano Concerto No 2 (1929)" on YouTube
https://youtu.be/X_7O09ucelM

I have a small 78 RPM Collection myself, and one of the 78 RPM recordings I have is Rachmaninoff Playing his Piano Concerto No. 3 in D Minor with the Philadelphia Orchestra w/ Eugene Ormandy Directing (I'm assuming the recording was from the same time period as your Rachmaninoff recording which would fo been between 1929 and 1931 and it is a recording meant to be used on a record player with an electrical pickup as opposed to an old mechanical pickup device like the old crank-up victrolas had.)

The records and the case/jacket are in mint condition.

The Rachmaninoff 3rd Concerto was recorded by the composer in 1939-40. By that time apart from portable record players, the living room record player was electronic. However in 1929, phonographs were still predominantly acoustic hence the recording equalization characteristics were governed by them. The characteristic in 1929 was "constant velocity" whereby the velocity of the stylus across the audio bandwidth governed loudness.

To improve disc signal to noise and also to increase playing time, a constant amplitude charactistic was introduced in the 1930's. Hence 1940 recordings played on an acoustic phonograph would have diminished bass frequencies and boosted highs, making the records sound shrill.

Unfortunately record equalization remains a little understood technological evolution which leads us to having to endure an obnoxious cacophony of Elvis Pressley and Eddie Fisher 78's on vintage 1910's era Victrolas at antique markets.

Been studying, photographing, drawing and documenting the construction of the mouse affected chassis. I have decided to dismantle the affected areas, clean the chassis bright and apply a coat of zinc silver paint over the cleaned portion. I shall only begin dismantling after the total documentation leaves no ambiguity how to accurately reconstruct.

Meanwhile, the speaker de-rusting was complete and a coat of silver paint applied. The speaker has been reassembled and tested.

If you need the large roundie socket I have an extra one for the B&K 467.
Your B&K socket is likely the 14-pin one, that is what my 467 included and what fit all of the 21-inch round color CRTs. The 15GP22 needs a similar size but 20-pin socket. I would very much like to have one of those if I could find one; I either made an adapter with a bunch of alligator clip leads, or I just used loose clip leads, when I tested my 15GP22.

Penthode, this will be a great project!

You’re in luck, this guy says he has like 17 of them...
I’d buy one, but I already have an adapter of my own.

https://www.ebay.com/itm/174268516102

You’re in luck, this guy says he has like 17 of them...
I’d buy one, but I already have an adapter of my own.

https://www.ebay.com/itm/174268516102

Thanks! Although the universal leads work well on the Sencore tester. But it would be nice to use the B&K.

I would have liked to find a replacement 20 pin base for the 15GP22 as the one I have has been epoxied to fill a chunk that was missing. Chance of finding a base will be much less than the socket!

Have been documenting and photographing extensively the IF stages and audio demodulator/ amplifier prior to dismanting the heavily rusted area.

Carefully drilled out the tag strips and tube socket and unsoldered and snipped away around the stages to lift portions complete away from the chassis. I will endeavor to keep as much as possible. But plan to replace at least 3 sockets heavily corroded and the last VIF located in the shielded box. The last IF socket appears very brittle from I suspect the enclosed heat. (I cannot get over there is six IF stages in all. It will be fun to re-align!)

You will see the chassis below cleared of components. I plan to go over the rusted area with Phosphoric Acid this prior to painting with zinc paint. I would like to reconstruct the chassis as close as possible to its original state apart from changing the paper capacitors to sprague orange drops.

Fortunately the rest of the chassis looks really good. Haven't ventured into the HV Box yet however...

RF-IF Alignment is actually not difficult. I had no trouble at all with my set.

Just be sure that if you replace capacitors and
resistors in the IF you keep part size and lead length as close as possible to original.
If you change resistors, it usually means using much higher wattage if you use film resistors (and be sure they are not the spiral cut kind). I replaced resistors in the IF with carbon composition ones; thankfully there were only a couple.

Thanks. Sweep alignment looks pretty straightforward. I inherited from an old TV station its extensive inventory of NOS carbon composition resistors and shall use them to match the original construction. The only improvement I shall include is replacing the capacitors with newer metal film units.

Some of the corrosion was pretty bad and I plan to clean the affected area fully. Sadly, as was the habit of many repair folk, the bottom panel was not refitted allowing the mice to easily crawl into the chassis corner. I was surprised the degree of corrosion the trickle down of the mice urine caused to the speaker below. Fortunately all is fixable: it just requires time and patience.

I considered a chemical de-ruster. However I have had good results using electrolysis. It is cheaper too.

With the chassis half stripped off, the chassis was immersed up to that point. The chassis is the cathode (-) and the carbon slab the anode (+). 5 Amperes for two hours.

Removed the chassis and lightly went over the derusted section with a rotary dremel brush and 0000 steel wool. Most of the cadmium plating remained: all on the top and about 80% on the bottom. I will apply some zinc paint over the affected areas to prevent it from rusting. The poor CT-100 looks like it had a tough early life and I intend keeping it in a climate controlled environment.

I have a lot of cleaning ahead. I want to first clean off the top of the rest of the chassis then proceed with reassembly. I will re-rivet the tube sockets and tag strips as original. Note the tubular rivets are available on eBay for abut $9 for 200 and free shipping from China! The IF tube sockets with shield clamp require 3/32"D x 7/32"L , the non-shielded tubes 3/32"D x 5/32"L and the tag strips 1/8"D x 1/8"L.

Cleaning, cleaning, cleaning. The mice really did a number on this old set.

Making progress. Stripped off the old soldered connections from the tag strips. Repaired a couple of broken lugs. cleaned and repaired the wafer 7 pin tube sockets. The ceramic Cinch brand 7 in socket used for the 6AQ5 audio output tube was fractured and replaced it with a Cinch type bakelite type.

The 6th video IF amplifier phenolic wafer tube socket had became very brittle due to heat and snapped. I think it is because the tube is located in an unventilated little metal compartment. Replaced it with a Cinch bakelite type. Fortunately the tube pin layout and the mounting holes of the replacement matches perfectly the wafer socket.

Dismantled the rusted potentiometers where the mice nested. Used the electrolysis bath to remove the minor rust from shells affected. A badly rusted metal shell I replaced with one that matched from one I found in an old TV shop's hoard I picked up years ago. I was given a car load of old Cigar boxes filled with reclaimed vintage TV and Radio parts from a shop long closed. I am sure the previous owner of all these reclaimed parts must be smiling from heaven.

With the chassis derusted and components cleaned, reinstallation begins. Re-riveted in the tag strips and awaiting now the delivery of the 3/32" rivets to re-attach the wafer tube sockets.

Here are some before and current state photos of the now vacated mouse abode. Note that the red patches in the after photos are the copper plating that was originally between the base steel and top cadmium. The mouse corner has been fully derusted and any exposed steel coated in zinc paint.

Great! Keep the reports coming.

Looks great and mouse damage really irritates me. Glad that you have the tenacity to tackle this step by step instead of chucking it into the bin.

Looks great and mouse damage really irritates me. Glad that you have the tenacity to tackle this step by step instead of chucking it into the bin.

Mouse damage is the worst. The corrosion is intense. Fortunately it was localized. The metal chassis shield in the cacinet immediately underneath the mouse abode was badly rusted. It has since been de-rusted. Fortunately the mouse corrosion results in minor pits where it went through the copper-cadmium plating and the metal has not been too much compromised. Two of the potentiometer connector pins were pretty severely rusted but salvageable.

Last couple of days, while waiting for the delivery of the remaining tube socket rivets, wired up the replacement 6thg (last) IF tube socket.

Also took time to pull the tuner, dismantle, clean and relube the massive tuner drum. Used electrolysis to clean off the surface corresion and nicotine. The original cadmium plating underneath looks pretty decent.

Very good, meticulous work.

"Mo Bettah"! Looks great.

Looks really amazing so far. Can’t wait to see beautiful NTSC color on it again in the future.

Penthode, your work is impressive. Please keep us up to date with all your accomplishments.

I do have a question. Why do mice like old TVs? Is there some food source such as cotton covering on old wires that attracts them? It's surely not warmth as these old TVs are not being turned on everyday. Could it be as simple as a place to bed down for the night?

Penthode, your work is impressive. Please keep us up to date with all your accomplishments.

I do have a question. Why do mice like old TVs? Is there some food source such as cotton covering on old wires that attracts them? It's surely not warmth as these old TVs are not being turned on everyday. Could it be as simple as a place to bed down for the night?

just a place to hide?

just a place to hide?

To hide yes because under the CT-100 it was pretty secluded. The previous owner obligingly left the cover off and the mice stuffed the underneath with tons of cotton which made it pretty cosy. I think the set was in a non temperature controlled environment from the look of it.

The problem is the mice appear untidy creatures as the unine soaked cotton against the steel chassis leads to pretty extensive corrosion. I would normally pass on a set in this condition but as this set is special and the CRT appers to have miraculously survived, the thorough overhaul of the affected region is justified. The aim will be to put it back together closely as possible the way it left the factory. With new capacitors, of course.

The rivets are scheduled to arrive on Monday which means I can begin rewiring the chassis once the tube sockets are back in place. I removed most of the IF strip as a loom only removing what was necessary to pull the assembly away. After a thorough wash, iit will be put back in place and connected,

Many of the components are salvagable after a wash. Many resistor leads and disc bypass capacitor leads were badly corroded. The Video IF decoupling capacitors are ceramic disc 820pf. DigiKey and Newark (I did not investigate Mouser this time lol) no longer carry the old style ceramic discs. I found a bag of old style ceramic disc 820pf on ebay and will use those as necessary. And the badly corroded carbon composition resistors will be replaced with identical looking carbon composition units.

"The Video IF decoupling capacitors are ceramic disc 820pf. DigiKey and Newark (I did not investigate Mouser this time lol) no longer carry the old style ceramic discs."

I looked ... both Mouser and Digikey have totally suitable, totally ordinary disk ceramic
caps. Both have over 40,000 in stock! I used these in my CT-100 (various values) and
they work and look just fine, albeit some are blue.

"The Video IF decoupling capacitors are ceramic disc 820pf. DigiKey and Newark (I did not investigate Mouser this time lol) no longer carry the old style ceramic discs."

I looked ... both Mouser and Digikey have totally suitable, totally ordinary disk ceramic
caps. Both have over 40,000 in stock! I used these in my CT-100 (various values) and
they work and look just fine, albeit some are blue.

Can you show me the link? I looked and the 820pf ceramics bore no resemblance to the original. I have previously used Newark, Digikey and Mouser for years.

The NOS I bought from eBay looks a very close match.

Mouser part numbers 594-S821K29X7RN63L6R or
75-562R10TST82 They have 19,047 of the top one in stock!

If you want NP0 there is 81-RDE5C3A821J2K1H3B but they are blue.

Can you show me the link? I looked and the 820pf ceramics bore no resemblance to the original. I have previously used Newark, Digikey and Mouser for years.

The NOS I bought from eBay looks a very close match.

I tend not to trust most capacitors, resistors, found on eBay anymore, and especially transistors :(
just too many fake parts.

I tend not to trust most capacitors, resistors, found on eBay anymore, and especially transistors :(
just too many fake parts.

I agree wrt ebay and transistors. I have been burnt a few times. However if the seller is in the US with what appears to be NOS vintage resistors and ceramic capacitors I have had no problems. When wanting to keep the original appearance I have patently searched for just the right part.

It must be just me. I even baulk at newer metal film resistors which do not match the older carbon composition resistors in older vintage equipment. For 1930's sets, I have a store of older dog-bone style resistors.

I used to restuff paper capacitor but do not bother anymore and certainly the gleam of an epoxy dipped capacitor does not look too out of place. I will use modern film capacitors of a higher breakdown voltage in order to ensure the component is of a physical size roughly equivalent or only slightly smaller than the original.I will always restuff electrolytics though.

Which reminds me, I have a question on capacitors used in 50's set vertical sweep circuits minus the blocking oscillator transformer. I have found that it appears the capacitors are critical in that proper capacitor characteristic choice is essential for maintaining good sweep linearity during warmup over a half hour or so. Has anyone else had this problem?

Been cleaning the considerable gunge off the chassis this week. Removed the high voltage compartment and the selenium rectifier frame to give it a thorough clean. Started replacing paper capacitors in the HV cage and now that it is clean have given it a thorough inspection.

Whilst making checks around the selenium rectifier, found a fuse blown and a jumper wire which had been placed across it. Not good. Then the resistive ballast if that is what it is called I examined and found part of it open. Closer examination revealed it appears to be simply a voltage dropped with an 800 ohm and a 300 ohm resistances to each drop the 400v DC supply to 285v. 115v across the 300 ohms dissipates 41 watts and 800 ohms 16 watts. The 300 ohm section is the one open.

It looks to me a bit of a bad design wasting 56 watts like this. That is a good chunk of the total 475 watts the setg consumes. I guess power was cheap in those days!

Anyhow think what can I do to salvage this? I found a 50 watt 330 ohm and 25 watt 820 wire wound chassis mount resistors back to back will just fit the 30cm diameter ballast container. But that is a lot of power to dissipate.

Has anyone else dealt with this or have any ideas?

Personally I'd rather stay true to the original design despite the 56 watts of heat given the rarety of replacement parts in the chain. An open resistor is far cheaper than a smoked transformer or buckled plate when a redesign goes haywire. Just my two sense

In my CT-100 I stared at the low voltage cage for days before deciding what to do.
I love the look of those huge orange selenium rectifiers.

But I also noted that the chassis mount can electrolytics were soldered down.
I decided that unsoldering all of them would be dangerous. Cutting them
all off near the base to restuff would be difficult and risky too.

So I decided to rebuild the whole B+ power supply with modern caps, 5 watt
silicon diodes, several fuses in various places, and large old-style Ohmite series 210
tapped (adjustable) resistors to drop voltages. In my
case the original ballast was OK and was left in series with the new Ohmites.

It put all those on an epoxy circuit board and mounted it in the cage.
I used the usual chassis clips to space the resistors at various distances from the board.

I set the line voltage with a Sola regulator transformer and a Variac ( permanently
mounted ... I inherited about 50 Variacs from a scrapped chem teaching lab)
so the filaments were exactly 6.3 and then adjusted the resistors so that the various
B+ voltages were exactly as Sams specified.

The fuses saved the 15GP22 from its first two arcs, as it got gassier and
gassier. But the third one, while it did blow the fuse, was fatal.

Have you ohmed out the vertical convergence transformer for shorts and opens yet? IIRC the original transformers were painted black while the modern reproductions were silver in color. You might have gotten lucky and have a reproduction.

I forget what the case was on my CT-100 (I think the previous owner addressed the power supply when they did a janky amateurish recap), but my 21CT55 (CT-100 factory modified to drive a 21AXP22) both ballast sections were open so I bought a couple of chassis mount high power resistors off mouser and found places on the rear upright where the resistor screw holes lined up with the cage screw holes. I gutted the original ballast and it now exists purely as decoration.

I also ended up replacing each selenium with 12 modern silicon diodes in series to emulate the original selenium voltage drop.

I forget what the case was on my CT-100 (I think the previous owner addressed the power supply when they did a janky amateurish recap), but my 21CT55 (CT-100 factory modified to drive a 21AXP22) both ballast sections were open so I bought a couple of chassis mount high power resistors off mouser and found places on the rear upright where the resistor screw holes lined up with the cage screw holes. I gutted the original ballast and it now exists purely as decoration.

I also ended up replacing each selenium with 12 modern silicon diodes in series to emulate the original selenium voltage drop.

It was a very good thing you replaced the selenium rectifiers with modern silicons, as seleniums can short and give off a very unpleasant-smelling gas when they fail.

I did not realize, however, that you needed to replace the selenium rectifiers with 12 silicon diodes, for a total of 24 silicons. I am thinking your TV used two selenium rectifiers, as a lot of 1950s TVs did; my folks' second TV, a Crosley Super V from about 1955, had two seleniums in the LV power supply. (Their first television, a 1954 RCA Victor 21" console, had a 5U4 LV rectifier, IIRC.) These selenium rectifiers, IIRC, were still good when we finally put the Crosley Super V in the basement in 1965 (where it, and the cabinet of the 1954 RCA, remained until 1972; long story and OT), replacing it with a Sears Silvertone all-channel 17-inch b&w portable shortly thereafter (at my mother's insistence, as she wanted an all-channel TV by this time; the reasons for that are OT for this thread).

Now that your TV has silicon LV rectifier diodes to replace those seleniums, you won't have any more trouble with the rectifiers for a long time unless they short again, giving you one less thing to be concerned about. However, this shouldn't be an issue; if the rectifier diodes short again, the TV's line fuse(s) or circuit breaker, of course, will open immediately, so you will know beyond the shadow of even the most unreasonable doubt that there is something wrong in the power supply.

I never understood why selenium rectifiers caught on - they seemed to be a headache, even then. Was the filiment requirements for two 5U4s that much?

I never understood why selenium rectifiers caught on - they seemed to be a headache, even then. Was the filiment requirements for two 5U4s that much?

With the 5U4 filaments at 3 amps per tube, I'll bet saving 6 amps with the selenium rectifiers made for an easier life for the power transformer :thmbsp:

In my CT-100 I stared at the low voltage cage for days before deciding what to do.
I love the look of those huge orange selenium rectifiers.

But I also noted that the chassis mount can electrolytics were soldered down.
I decided that unsoldering all of them would be dangerous. Cutting them
all off near the base to restuff would be difficult and risky too.

So I decided to rebuild the whole B+ power supply with modern caps, 5 watt
silicon diodes, several fuses in various places, and large old-style Ohmite series 210
tapped (adjustable) resistors to drop voltages. In my
case the original ballast was OK and was left in series with the new Ohmites.

It put all those on an epoxy circuit board and mounted it in the cage.
I used the usual chassis clips to space the resistors at various distances from the board.

I set the line voltage with a Sola regulator transformer and a Variac ( permanently
mounted ... I inherited about 50 Variacs from a scrapped chem teaching lab)
so the filaments were exactly 6.3 and then adjusted the resistors so that the various
B+ voltages were exactly as Sams specified.

The fuses saved the 15GP22 from its first two arcs, as it got gassier and
gassier. But the third one, while it did blow the fuse, was fatal.

I have stared at this set's power supply and haven't decided anything yet. I would like to keep it original especially if the selenium rectifier are good. I have generally had no problem with the seleniums unless there was a B plus short. But the fuses are there for protection.

I was thinking of fitting a 50W wirewound resistor in the ballast tube. But 41watts? I wonder if the resistor would survive? Maybe remove the seleniums and use the space to mount some old style porcelain 100w Ohmites?

Have you ohmed out the vertical convergence transformer for shorts and opens yet? IIRC the original transformers were painted black while the modern reproductions were silver in color. You might have gotten lucky and have a reproduction.

Yes that was one of the first thing I did. I lifted the secondary and did not see the VTVM needle quiver which suggests the leakage resistance is greater than 1000 Mohms.

Only received the rivets for the tube socket remounting yesterday. The rivets are 3/32" x 1/4" and the 1/4" length was needed for the phenolic wafer socket + tube shield bracket + chassis thickness. Had to drill each rivet core by an additional 1/32" and reduce the diameter of rivet head from 0.200" to 0.150 to match the original over heads.

Supported the front chassis section with books and a punch was clamped in a vice below the chassis for the head of the rivet to rest. Then used the hammer and rivet tool on the topside to spread the rivets. Two sharp taps and a couple of finishing tops to ensure the tube socket is firmly secured.

The tube sockets are back in place and along with the IF and Audio Ratio Detector transformers. Currently replacing the potentiometers and soon will commence rewiring.

So much cleaning to get rid of the mess left by the previous tenants. Looking much cleaner now. And in case you forgot how bad it actually was, go back to page two of this thread to have a look!

This week's update: I have completed the reinstallation of the video and sound IF and audio amplifier wiring to the previously mouse encrusted region. I am awaiting a couple of capacitors and that's it. I shall reattach the front section of the chassis next week and reintegrate the two. I reckon it has taken about 60 solid hours of effort to get this far.

All of the resistors in the mouse infested area are new as are the capacitors. I reused the pots after dismantling and cleaning. All of the resistors are NOS old style brown body resistors.

The high voltage box which was removed has been cleaned and all capacitors (apart from the doorknobs) have been replaced.

Have been meticulously following the dozens of photographs taken from different angles as well as refering to the schematic to confirm connections. I took copious notes when dismantling but have hardly needed to refer to them.

Still have to finish replacing the paper dielectric capacitors on the front section and a large bunch on the main chassis.

Beautiful!

What percentage of the work would you say has been done towards first light?

Beautiful!

What percentage of the work would you say has been done towards first light?

What percentage? I feel I am almost to the point where the real restoration may begin. Re instituting the removed chassis section will take another full day to do it properly. And then replacing all the paper capacitors and tidying up previous repairs. The power supply needs work: what to do with the ballast resistor And all the filter electrolytics. RCA used excellent quality electrolytics in the late 40's and early 50's so I will be curious how the CT-100 filters will be. And there is refinishing the cabinet while the weather is good.

I would like to think I have nearly reached the 50% point before the first power.

I have learned a lot about the curious nature of the CTC2 chassis design. It does not feel like a big run chassis from a number of little anomalies I have found such as component placement. Certainly with the high number of power resistors, at 475w it is not a power efficient design.

In the day when an uninsulated home was heated with electric resistance another 475 watts was not a big concern

Getting the subchassis's prepared for putting them back together. And scrupulously going over connections and components.

I make ote of the Peter Deksnis alert for the 6BK4 HV Regulator replacement for the 6BD4. As he discovered, pin 8 on the tube socket is used as a tie point for the original 6BD4 circuit. Substituting the later 6BK4, it has a pin 8 interconnection to the cathode.

https://www.earlytelevision.org/Deksnis/caution_6bd4-6bk4.htm

I added a tag strip wiring point to carry the connection away from pin 8 of the tube socket as,depicted below. After this last item, I recounted the HV cage back to the main chassis.

The CRT socket HV leads for the electrostatic focus and convergence electrodes had deteriorated and,were,about to fall off. I missed out on the one recently for sale on eBay. Taking the socket apart, revealed the HV electrodes encapsulated in a molded plastic piece. I had to break the plastic surround to remake the connection and in the process of making a small plastic surround replacement.

The vertical integrator leads were corroded from my mouse friends to the point one lead easily disintegrate and dropped off. For those familiar with these things, it is a Central "Couplate" number PC-101. I decided to remanufactured one as it has only a few passive components: a 002uF, two .005uF and 22k and 8.2k resistors. I ordered from Digikey some surface mount chip components I will put on a little board less than the size of the original couplate.

I assembled my replacement for the PC-101 couplate this evening. Parts cost about $1. Cheaper than the Centralab unit.

Surface mount resistors and capacitors on a scrap board. The 0.01uF cap is a small ceramic disc mounted on the rear.

Making more progress on the CT100. The reunited wiring is complete! Spent over a dozen hours reuniting the HV cage and the front section including the IF amplifiers to the main chassis. Laboriously checking photographs, my notes and the schematics (as there are variations) finding where the approximately 35 wire and components originally went. The photos help ascertain the original lead dress.

Some of the original wiring looked messy. I tried to clean up some of the worst congestion but ensured, especially around the IF sections I had to fully remove, that it was as close as possible to the original layout.

Next comes the replacement of the remaining paper capacitors. I tested a few and the leakage is incredible. It only goes to prove that plugging in any set of this vintage or older without addressing the paper caps is crazy.

As for the electrolytics, I aim to see if they will reform with low leakage. It will be easy to weed them out and if there is any doubt, out they go.

Here are some photos where this CT100 is now. Note the lower right which was previously the mouse abode.

Great!

Glad to see you recognize the importance of routing to proper function and are avoiding changes for the sake of visual neatness in the high frequency areas. You probably also know that routing and grounding points can affect the coupling of sweep currents (horizontal ringing "jail bars") into the video, but thought I'd mention it here for others who may be newer in the hobby.

Been going through the chassis this evening. Every one of the white blob peaking coils is open circuit: 180uH, 1.0mH, 1.6mH, 1.9mH and 3.6mH. The biggest ones are in the I and Q chroma channels.

I have an NOS Meissner 180uH replacement. But it is difficult sourcing the others. Anyone know a good source of supply?

I found on Amazon a spool of 44 AWG magnet wire and may end up winding them myself. Easy to measure the inductance but achieving the correct Q may be a bit of a challenge.

As to peaking coils: don't try to find NOS ones. Just get the small to medium
size (size of old fashioned 1/2 or 1 watt carbon resistors) cylinderical axial
ones from Bourns or API Delavan. Get shielded if they have them. Make sure
the self resonance frequency is high enough.

I do very strongly recommend that you don't use the approx 6 mH specced
for the Q channel ... it seriously ruins the chroma reaponse. Get one that's in the 2.7 or 3.3 mH range.

They don't look right but work very well. You may need to search both Mouser and Digikey to find all values.

The picture on my CT-100 is the best recommendation for these.

The coil's Q is not a problem, all of those coils are plenty good enough because they
have ferrite forms. The shielded ones also have ferrite outer shields.

I was able to get an assortment of peaking coils quite reasonably from Moyer electronics in PA to solve the same problem I had with my Hallicrafters set.

I was able to get an assortment of peaking coils quite reasonably from Moyer electronics in PA to solve the same problem I had with my Hallicrafters set.

That is good to know. I will check it out. Thanks.

I do very strongly recommend that you don't use the approx 6 mH specced
for the Q channel ... it seriously ruins the chroma reaponse. Get one that's in the 2.7 or 3.3 mH range.

After thinking about this a bit, I believe the large inductance was to specifically limit the Q bandwidth to roll off at 500kHz. The I channel is 1.5 MHz wide.

Remember the I and Q are transmitted vestigial sideband in quadrature which means extending the Q bandwidth will lead to quadrature crosstalk. Further in this early design both Y and I channels have delay inserted to align with the limited bandwidth Q channel: Y a larger delay than I. Reducing the peaking coil inductance will extend the Q bandwidth which will reduce the delay.

All sets I believe following the 21CT55 used equa-band narrow channel (500kHz) chroma demodulation apart from my CTC5 Deluxe which has a equa-wide-band chroma demodulator. This means the CTC5 Deluxe intentionally introduced quadrature crosstalk in what appears to be an attempt to increase marginally chroma resolution. The crosstalk is noticeable at abrupt color transitions. (There was a 1955-56 RCA review I recall reading about this many decades ago. I need to look for it).

So I am going to investigate this further. Certainly I can do some tests with the peaking in circuit resonance with the technique outlined in my Measurements Lab. Grid Dip Meter applications notes pertaining to video amplifier design which outlines how to determine peaking coil inductance in circuit.

After thinking about this a bit, I believe the large inductance was to specifically limit the Q bandwidth to roll off at 500kHz. The I channel is 1.5 MHz wide.

Remember the I and Q are transmitted vestigial sideband in quadrature which means extending the Q bandwidth will lead to quadrature crosstalk. Further in this early design both Y and I channels have delay inserted to align with the limited bandwidth Q channel: Y a larger delay than I. Reducing the peaking coil inductance will extend the Q bandwidth which will reduce the delay.

All sets I believe following the 21CT55 used equa-band narrow channel (500kHz) chroma demodulation apart from my CTC5 Deluxe which has a equa-wide-band chroma demodulator. This means the CTC5 Deluxe intentionally introduced quadrature crosstalk in what appears to be an attempt to increase marginally chroma resolution. The crosstalk is noticeable at abrupt color transitions. (There was a 1955-56 RCA review I recall reading about this many decades ago. I need to look for it).

So I am going to investigate this further. Certainly I can do some tests with the peaking in circuit resonance with the technique outlined in my Measurements Lab. Grid Dip Meter applications notes pertaining to video amplifier design which outlines how to determine peaking coil inductance in circuit.

I think you've got it right. Since the Q coil is large, it's resonant frequency probably is also more critical - too low and you could bite into the 500 kHz bandwidth and get ringing. Going the other way, a little quadrature distortion could be hard to see on a small screen.

Going through the chassis replacing capacitors and the odd resistor. The previous owner replaced a number of capacitors it appears years,ago with orange drop Spragues but left long leads on the replacements. Tidyi g up as I go along.

I saw a little wire jumper under the chassis I initially thought was jumping an old fuse. Found it bridged the power switch. I pull out the switch and found it quite charred. It was a Centralab switch and potentiometer so I proceeded to look though my box of old parts. Found many exact physical replacements. However I found that all the other switches fitting the control were only 3 amps and the burnt out switch was rated 5 amps. Think about it: this set dissipates 475 watts which means it must drawabout 4 amps! To avoid any physical modification to the control, with the 3 amp swich unit now married to the old CT100 control, there is space underneath to fit a 15 amp @ 115v Potter Brumfield relay.

I amazes me the power this beast consumes!

Making further progress. Hoping to within the next couple of weeks power up the chassis minus the CRT.

Replaced most of of the paper capacitors. This chassis takes a lot and awaiting an order from Digikey to complete.

Reforming the can electrolytics: all coming up with low leakage after a few hours feeding a 10mA current limited supply. It looks like this set has sat dormant for the past 40 to 50 years as all the earlier replacement capacitors are quite old themselves now. Despite that, the electrolytics came back from almost a dead short to holding full rated voltage with less than 100uA leakage in just three hours. Not bad. We will see how they fare.

The design uses early cartridge electrolytics for DC coupling in the chroma stages and despite coming back with low leakage, I am substituting new ones. The 4uF 450v units are on order from Digikey.

My power switch solution entailed installing a 120vac relay. The relay contacts are rated at 25A at 120vac. It was interesting to note the original Centralab 5A switch on the volume control physical form factor matches the standard 3A switches. I can picture in my mind RCA Victor engineers calling the Centralab engineers in around 1953 asking them to beef up the specs from 3A to 5A and the incredulous Centralab people replying "What the heck are you powering?"

Anyhow, the photo below show the fitment. The replacement 3A switch on the volume control now only has to energize the relay.

I shall be substituting 3A silicon diodes for the old Federal selenium rectifiers. And still considering various solutions for the super hot voltage dropping resistors.

The KRK12 tuner unit has been fully dismantled, cleaned and lubricated and is ready to re attach to the main chassis.

'I can picture in my mind RCA Victor engineers calling the Centralab engineers in around 1953 asking them to beef up the specs from 3A to 5A and the incredulous Centralab people replying "What the heck are you powering?" '

It's the bread/bagel switch! :D

I have been considering replacement of the Selenium rectifiers. They are connected in a full wave volage doubler arrangement. I plan to replace them with a pair of 1N5208 diodes which are rated at 3A with a peak inverse voltage of 800volts.

First I thought I should test the old Federal units to determine their current state and performance. I calculated the typical full B supply current from the schematic diagram as indicated in the photos below. The full load current appears to be 600mA and I used my adjustable low voltage bench supply to see what the forward volatage drop of the selenium rectifier is at 600mA.

I was surprised to find the drop only to be 10 volts. If I was to substitute silicon diodes and ignoring the junction drop of about 0.6 volts, the series resistance to effectively account for the diode substitution works out to be 15 ohms. Power dissipation would be 10 x 0.6 = 6 watts so I should get away with a 10 watt resistor.

I am curious as to the failure mode of selenium rectifiers. I understand the forward resistance rises with age. But 15 ohms at 600mA does not seem bad and both rectifioers have almost identical forward resistance. I suspect that the rectifiers may reach a point where the dissipated heat leads to a thermal runaway situation. Will need to do more research on this.

Not: In my forward voltage drop test, I arbitrarily used 10 ohms in series as a current limit as I brought up the voltage supply. The voltage aimed for across the series load resistance was 6 volts which woulkd man 600mA is flowing.

Dunno how true it is, but I've heard tell that reverse leakage in aging seleniums can contribute to heating. Might be urban legend though.

Logically, the power dissipated by reverse leakage would be minimal unless the selenium rectifier broke down. My understanding is that the forward resistance increases with age. And as the forward resistance increases, the power dissipation would increase. Thermal runaway would occur if the resistance increased with temperature.

I have completed the paper capacitor replacement as well as the disassembly and reassembly of the IF stages to clean out the mouse nest. Last two remaining jobs:
1) Replace/fix the open peaking coils.
2) Arrive at a solution for the dropping resistors (ballast).

Peaking coils: All of the white encapsulated coils are open. The white concrete like covering of the coils was a really bad idea. I managed to salvage two by carefully crunching off the white exterior and fishing for the coil ends. There were signs of green "vertigris" at the wire ends. I managed to find the ends and reattached. However I still need a couple of 1000uH and the 6900uH coils.

I reflected on the design and have dismissed the substitution of different coil values. The I and Q channels have predetermined bandwidths of 1.5MHz and 0.5 MHz respectively. The coils in the I and Q channels facilitate the different bandwidths hence the values must be maintained. Further, the wider I channel has a delay inserted to align the narrower Q channel so it is important to ensure the bandpasses remain as designed to minimize display chroma registration and alignment.

I am awaiting the delivery of a spool of AWG44 wire and contemplate making some coils myself. Once installed, I shall sweep I and Q channels in the course of overall alignment and testing of the chassis prior to attaching the 15GP22.

2) Ballast Resistor: I have decided to mount the 315 ohm 50W and 800 ohm 25W resistors on a heat sink assembly which will plug into the ballast socket. I decided again using the chassis itself as a heat sink and/or mounting the ballast resistors over or near the selenium rectifiers as I want to keep the heat source isolated as much as possible from the CRT bell. I am concerned the temperature source will be detrimental to the CRT.

Also note I decided against using the selenium rectifiers. I have left the rectifiers in situ disconnected and immediately below them have installed a tag strip to which is attached two 3A 800piv rectifiers and a 10 ohm 25W dropping resistor.

I shall be assembling the ballast replacement this week. The electrolytic cans all check okay and the capacitors have been reformed. I should be on target for a first power up this next weekend.

I have been making progress with the peaking coils. I have managed to repair three and found a way to accurately measure and recreate the missing coils.

I have been looking for a way to accurately measure peaking coil inductance. The best solution which is repeatable is resonating it against a known capacitance. I am using the setup below.

I am series resonating so as I adjust the oscillator, I will find a dip when resonance is found. I am using a 5% 820pF mica capacitor. (I could not find a 1% tolerance cap). The capacitor is slightly higher than 820pF so my readings are consistently a few percent below. But it is close enough.

The repaired 1.9mH measured resonance an inductance of 1.85mH. The 820uH inductor measure 800uH. and the 1.0mH coil measure 980uH. So all is good.

I am now in a position to recreate the 6.7mH and another 1.0mH to complete the set.

When the set is back together, I shall sweep the chroma and luma channels with the new peaking coils to ensure this CTC2 chassis meets spec.

Going nicely!

Edit: If you short the 820 pF you could also measure the self-resonant frequency, although you will have to correct the result due to the scope probe capacitance.

Going nicely!

... If you short the 820 pF you could also measure the self-resonant frequency, although you will have to correct the result due to the scope probe capacitance.

Measuring the self resonant frequency is an interesting thought, The original peaking coils are machine wound in a pattern to minimize self capacitance. My winding is by hand bunch wound which inevitably will affect self capacitance.

It would be interesting to compare a coil I make by hand with a NOS Merit machine wound coil which is first made to match resonance with the 820pF and then tested for self resonance. The peaking coil is designed to resonate with the circuit self capacitance hence my winding may skew in-circuit performance.

This will all become apparent on the final I and Q channel frequency sweeps.

I knocked together a CT-100 ballast resistor replacement on the weekend. It plugs into the ballast socket.

I bought 350 ohm 50w and 800 ohm 25w chassis mount resistors and attached to a heatsink I bought on Amazon for another project. The octal male plug was from a relay and was mounted on an angle so that when plugged into the CTC2 chassis, the fins sit upward.

I used fiber glass spaghetti on heat resistant wire to the socket. The aluminum bracket attaching the heatsink to the octal plug was fashioned from a scrap aluminum plate or bracket my my scrap bin.

It will plug into the rear facing CTC2 ballast socket above the power transformer and will deflect and isolate the heat source away from the 15GP22.

The chassis is complete apart from two peaking coils. This evening with the chassis on the bench and everything connected except for the CRT, I plan to insert the tubes and provide the power up of the chassis in in over 40 years.

Last night I powered up the chassis. The power supplies came up and with the new ballast resistors installed, the voltages appear correct.

The only immediate issue was no audio. I had expected the rush of noise from the speaker and traced it to a short from the plate of the 1st audio IF to ground. Unsoldered and removed the plate connection and the short went away. Reconnected and I heard the rush of noise on power up and then it disappeared. Reasoned that the RF and IF were being biased off so a slight rotation of the AGC control brought up the rush.

Connected the Zenith set top box with its modulator on Channel 3 and I can hear program audio. Looks like all my video audio IF rewiring was okay.

Have made preliminary measurements through the chassis and all seems well. The high voltage is at 22kV and the regulator is working as I can swing it up and down with adjustment. Horizontal sweep is on frequency. The photo below the chassis is running and you will see the Heathkit VTVM reading 22kV with my Heathkit probe. (I bought the Heathkit IM18 VTVM as,a kit in 1971: hard to believe I have been using it for 51 years!)

My ballast arrangement is fine. With the heat sink, the temperature levels at 55 degrees Celsius which is much lower than I had anticipated. And that is with the correct voltage drops to the two B plus branches.

I still am missing a 1mH and 1.9mH peaking coil. The 44AWG wire arrived and so I think I will have a go at that tonight.

The chassis has run about half and hour with no issues.

The easiest and best way to measure the self-resonant frequency of a coil
is with a grid-dip meter and freqency counter or SDR receiver to get frequency accuracy.

That's if they are unshielded. If shielded, feed from a signal generator
through a 270K resistor and measure with a very low capacitance scope probe:
hook a 0.5 or 1 pF cap inseries with a short piece of coax. IF picky you can of course calculate the unloaded frequency.

I used both methods on my commercial ones for my CT-100 and they agreed.
I suspect you will be appalled with the frequency response of the Q channel.

The easiest and best way to measure the self-resonant frequency of a coil
is with a grid-dip meter and freqency counter or SDR receiver to get frequency accuracy.

That's if they are unshielded. If shielded, feed from a signal generator
through a 270K resistor and measure with a very low capacitance scope probe:
hook a 0.5 or 1 pF cap inseries with a short piece of coax. IF picky you can of course calculate the unloaded frequency.

I used both methods on my commercial ones for my CT-100 and they agreed.
I suspect you will be appalled with the frequency response of the Q channel.

Yes I have my Measurements Lab Grid Dip meter and plan to use to test it in that manner. However I have had consistent and pretty accurate results resonating the coil with my signal generator and frequency counter.

What is appalling about the Q Channel response? It is suppose to cut off at 500kHz. I was hoping to perhaps tailor it once I do the sweep.

I have been testing the circuits. I have audio and I can see some composite video. The Horizontal oscillator is properly locked but I have concerns about the vertical lock. I first need to do a complete IF alignment as I expect the IF response to be pretty horrible having had to reconstruct the strip.

I next need to fashion a jig to inject the frequency sweep to the mixer input.

I for one am very anxious to see the first power-up post-peaking-coils.

I for one am very anxious to see the first power-up post-peaking-coils.

In other words... it has piqued your interest! :D

Could not resist! :P

In other words... it has piqued your interest! :D

Could not resist! :P

Brilliant!

Haven't gotten arond to addressing the peaking coild yet. Hopefully this evening.

Neverthe less have been letting the chassis run. I reformed the electrolytics before powering and they seem fine. All the voltages seem correct so far up to the sync separator. I can see composite video on the scope and horizontal sync good. V ertical a bit touchy. Remember I recreated the couplate PC-101 integrator network. Seems the problem goes back to the vertical sync separator where the voltages are a bit low and the sync output appears a bit low.

The HV is holding at 21 kV. The vertical convergengence transformer seems fine so far.

A longer run for over an hour produced the new resistive ballast unit temperature reaching 75 degrees celcius. Too hot to leave your finger on but a lot less than the 125 degrees I measured when it was clamped to the chassis.

What is appalling about the Q Channel response? It is suppose to cut off at 500kHz.

On my set both the white original coil ... which measured OK at low frequencies ... and a NOS 6 mH coil had a high frequency 3 dB point about 200 kHZ and it was way way down at 500 kHz.

I tried changing the 22 pF cap to ground to 10 pF and that upped the 3 dB frequency but resulted in a visible and actually irritating timing mismatch: the Q was too early. I experimented and found that the best overall was about a 3.3 mH peaking coil and an 18 pF plate to ground cap. This has the transition a bit early and a bit of orange line at the green to violet transition but the brightness error is about at the right spot.

In my personal opinion they really needed just a bit shorter delays for Y and I.

The only problem is the very rare violet to green transition. Green to violet is OK as is either violet or green to or from gray. See the I-Q only test pattern. IF you turn off the color entirely on this pattern you see only
the white and black areas ... the rest is constant gray.

http://www.videokarma.org/attachment.php?attachmentid=204667&stc=1&d=1659728707

http://www.videokarma.org/attachment.php?attachmentid=204665&stc=1&d=1659728096

1) Agree that 200 kHz was not right, but unless the 6 mH is a misprint, there ought to be some other problem causing it
2) The bit of orange at the green-violet transition is most likely due to quadrature distortion of Q into I, especially if you are using a test pattern DVD and going in RF. It is not due to something wrong in the set itself. The distortion mechanism is that the original pattern was generated as RGB full bandwidth, then the MPEG 2 chroma channels cut this down to equiband (R-Y) and (B-Y) chroma with perhaps 1/2 luma bandwidth, so the Q channel in the signal is wider than 500 kHz and actually made by the proper proportions of (R-Y) and (B-Y). Then the IF/video detector in the set cuts off the upper sideband due to the sound trap(s), leaving some unbalanced lower Q sideband.

Also note that there is no noticeable ringing in the +/- I transitions, so the ringing in the Q transitions must be at least partly due to the Q channel filter.

I think it might be possible to improve the Q transients. The way to work on this visually is to disable the I demod so you eliminate I quadrature effects; or use a scope to look at the I and Q signals separately.

dtvmcdonald, did you verify the value of L47, 1.9 mH?

I believe it resonates with the input capacitance of V10, Q phase inverter, and those two values could be critical in the high frequency response.

Peaking in tube circuits is a pain because tube circuits are generally high impedance and variation in stray capacitance is an issue.

A further thought: the self-resonant frequency of L47 could have been intended to be a big part of the peaking effect, so if it was replaced by a coil with a higher self-resonant frequency, that could cause a problem.
If that's the case, a small cap across L47 might increase the peaking.

The images I posted were with equal bandwidth I and Q from the source,
files on a USB key played on my Sony Blu-ray player.

I have files that are bandwidth-limited in Q and the orange artifact is much less visible. So far I can't find the screenshots of them.

It takes at least 50 pF across L47 to resonate it at about 500 kHz ...
and results in intolerable ringing.

Both screen appearance and measured waveforms concur with what a carefully done simulation,
including the tubes and stray capacitances (in many cases actually measured while changing parts) shows.

In any case, what I show is what I use at the moment, and results in the best overall pictures from
real DVDs (not Blu-rays) and the output of my digi-converter box fed into a top end
Blonder-tongue modulator, tested on channels 3, 8, and 39 (I have a channel 39 UHF strip).

Replies in bold

The images I posted were with equal bandwidth I and Q from the source,
files on a USB key played on my Sony Blu-ray player. Okay- good

I have files that are bandwidth-limited in Q and the orange artifact is much less visible. So far I can't find the screenshots of them. Okay -good

It takes at least 50 pF across L47 to resonate it at about 500 kHz ...
and results in intolerable ringing. That kills that speculation!

Both screen appearance and measured waveforms concur with what a carefully done simulation,
including the tubes and stray capacitances (in many cases actually measured while changing parts) shows. Nice. Why it would have been so bad with the specified part is a mystery then. Hard to believe they wouldn't have fixed this.

In any case, what I show is what I use at the moment, and results in the best overall pictures from
real DVDs (not Blu-rays) and the output of my digi-converter box fed into a top end
Blonder-tongue modulator, tested on channels 3, 8, and 39 (I have a channel 39 UHF strip).

Changed comments from "check" to "okay - good" because I didn't mean to tell you to check anything.

Have been reading your interesting comments on the peaking coils. Working on the peaking coils tonight: the two 1mH coils in the I channel. A previous repair replacement for one was 400uH and the other was open and unfixable. The 6.7mH and 1.9mH peaking coils have been installed in the Q channel.

Have been doing some further power up tests (with scope and multimeter). Found an AGC fault: picture overload and inability to adjust with AGC control. Found two resistors at V17 AGC Keyer 4.7M and 2.2M at the control had drifted upward. RCA notes said later chassis's substituted 3.3M for the 4.7M. Replacements made and now can set AGC to the point sync starts to clip.

Getting good horizontal and vertical sync and traced good luma to first Video amplifier.

Ballast Resistor maximum temperature after an hour run reached and sat at 75 degrees Celsius. Happy with this as the temperature is close to my target max and the heat is properly deflected away.

After the peaking coils with the chassis essentially complete will next focus on constructing the jig to inject the IF alignment generator to the tuner. RCA obliged with the details and I have my fabricating tools ready.

Still a few weeks away from testing the I and Q channel response and look forward to comparing results.

Still fussing over the power supply.

To accommodate the inherent forward resistance of the selenium rectifiers when replacing them with silicon diodes, I initially inserted a 10 ohm 15W resistor in series with the AC feed to both diodes. I had been powering the chassis and didn't initially pay much attention until I noticed the resistor leads appeared to be blueing! The ac voltage drop across the resistor measured 20 volts. At 2 amperes, the resistor was dissipating a whopping 40 watts!! And it survived!!

So rethinking this I initially determined the forward resistance of the selenium rectifier was 10 ohms at 600mA. That is 600mA per diode whereas my 2 amperes above was a culmulative measurement of both silicon diodes as the circuit is a full wave doubler where each diode conducts only 180 degrees.

I did find that the B voltages were low at an input of 118vac. The higher selenium resistance may be due to aging of the rectifiers? Just to note I left the selenium rectifier running under test at 1 ampere for half and hour and it was only moderately warm. My guess is the fins may help to better radiate the heat?

Nevertheless, I next tried attaching a chassis mount 50W 8 ohm resistor to the chassis upright with a little bit of silicon grease to reduce the thermal resistance. Boy did that heat the chassis! The surrounding metal after five minutes was too hot to touch and after 10 minutes or so the whole upright section was pretty warm.

As the B voltages were a tad low, it made sense to reduce the series resistance. with about 4 ohms and an AC input of between 115 and 120 vac at the set input, the B voltages were close. It is interesting to note that as this beast consumes 475 watts to load down the mains supply!

I had an old pack of 1.5 ohm Ohmite ceramic 11 watt resistors. With three in series, I measured a voltage drop of 8 vac which means that the resistors are dissipating each about 10 to 12 watts. I have mounted them suspended on a tag strip and left the set running half an hour. The surface temperature at the center of the resistors as measured with an infrared thermometer shows 205 degrees celcius! they are mounted directly under the old selenium rectifier (left in place for appearance) and the chassis remains relatively cool (45 degrees celcius and the adjacent electrolytics remain cool: one electrolytic has a cardboard shroud and the other measured 35 degrees celcius after half an hour, I am going to leave it here and it will be a good test to see how these Ohmite resistors last while running at 100% of rated capacity. (If they fail, they will simply go open and they are in seies with the 4.5 ampere fuse).

You will see below photos of the three Ohmite resistor location and the silicon diodes on the opposite side of the chassis upright. I have included a photo of my ballast resistor concoction with the surface mount resistors on the heatsink. The Infrared Thermometer reads about 80 degrees celcius maximum when pointing directly at the resistors from below as mounted. I am happy with this solution as it plugs in to the original ballast socket with no modification.

The chassis has been running fine on the bench (minus CRT) with it tuned to local programming thru a Zenith DTV box. Listening to just audio all day.

Next is to construct the input head and an IF test block to begin the sweep alignment.

I shall be using my HP8601a Sweep Generator and HP8600a Digital Marker Counter.

I had been powering the chassis and didn't initially pay much attention until I noticed the resistor leads appeared to be blueing! The ac voltage drop across the resistor measured 20 volts. At 2 amperes, the resistor was dissipating a whopping 40 watts!! And it survived!!...

I had an old pack of 1.5 ohm Ohmite ceramic 11 watt resistors. With three in series, I measured a voltage drop of 8 vac which means that the resistors are dissipating each about 10 to 12 watts.

I'm not sure I follow the second set of power calculations above, but in general, the actual power dissipation in rectifier series resistors is far higher than what you would calculate based on a voltage drop measurement. Since the diodes only conduct briefly at the peak of the waveform (to recharge what has drained off the first filter capacitor), the current during this short interval is far, far higher than the average current. Likewise, the voltage drop is higher than might be expected based on average or RMS AC current for a sine wave. With the current compressed into such a short interval with very high current, and the power dissipation depending on the square of the current, the actual power dissipation is much higher than expected.

So keep in mind that the usual power, voltage, and current calculations only work for DC current or sinusoidal AC current (with RMS value for the sine wave). Once you go to pulsing current in a rectifier circuit, things are quite different!

The instantaneous power, voltage, and current still follow the usual relationship, but the relationship between instantaneous current and average current is no longer so simple.

....the instantaneous power, voltage, and current still follow the usual relationship, but the relationship between instantaneous current and average current is no longer so simple.

Thanks Tom for your input and analysis. You are absolutely correct that my measurements are out the window as far as pulsing voltages are currents are concerned.

I have left the trio of 1.5 ohm 11W resistors in series with the silicon diode rectifiers I installed and they are pretty hot. I loomed at the Ohmite recommendations and the temperature is well within the range Ohmite specifies. And the B plus voltages are near correct. I will leave as us for now.

Saturday afternoon made the input block attached to the KRK12C tuner using the dimensions from the CT-100 manual. The RF sweep signal is applied to the mixer diode in the tuner and using and alligator clip there is awkward. The input block position is reinforced with a sprung clamp around a transformer can a well as the two phenolic pins with straddle two holes on top of the tuner.

This will be used to perform the IF alignment and chroma channel as well as facilitating full sweep tests as outlined in the RCA Service manual.

Now on to the testing and alignment this week.

Saturday afternoon made the input block attached to the KRK12C tuner using the dimensions from the CT-100 manual...

Wish they did something similar for the CTC-5. That connection is so sensitive to lead length/dress.

Wish they did something similar for the CTC-5. That connection is so sensitive to lead length/dress.

Funny you mention the CTC5. A decade ago, when I was using the HP8601a to sweep align my CTC5, the RF alligator clip slipped off and dangling touched the B plus. It blew up the output amplifier of the HP generator. I had used the generator successfully for over a decade and it is a brilliant generator for consumer equipment and was vey saddened by this!

I immediately searched EBay for a replacement part or even generator for parts and found a brilliant and enterprising engineer redesigned the 8601a output amplifier module and offered them for sale. I bought one and the 8601a now has a flatter output response than the original amplifier. Had to be patient on the CTC5 waiting to fix first the HP generator but it was worth it.

I am grateful fortunate that gains do often come after adversity.

The photo below shows the contact spring against stage mixer diode pin.

Decided to postpone the chassis alignment and bandpass evaluation while I fixed and refinish the cabinet. Peeling veneer relied and front mortised corners were separating. Glued with lot of long clamps all around to pull it back together.

Cabinet was badly banged up. Hoped not to have to do much sanding but had to fix many deep gouges.

Stained to match original finish. Came out very close to the finish removed. Two spray coats of Watco lacquer on the main cabinet to be lightly flattened and polished. Still to do lid and front wood control panel cover.

Seems to be a province wide shortage of lacquer products in Ontario at the moment. Found a hardware store 30 miles away had two litre tins which I collected on the weekend.

Very nice work.

Very nice work.

Thanks. There has been a lot of effort into this machine. I want to get the lacquering out of the way while the weather is good.

Looking forward to testing the completed chassis in September.

I must agree, a labour of love for sure. I too look forward to seeing a picture!

I finished the cabinet this evening. Two coats of lacquer: first coat, 400 grit wet and dry paper rub down, second coat, 600 grit paper followed by 0000 steel wool. The cabinet looks quite respectable now.

Before I head back to the chassis testing, I have run into a problem with the shadow mask. The black rubber surround seal has melted and amalgamated with the shadow mask. I tested removing a small portion at the corner with alcohol aided with a razor blade. The alcohol dissolves the red-brown paint. I dare not use the razor as it easily scratches the paint.

Any suggestions how to remove the rubber without removing the paint?

I finished the cabinet this evening...
Any suggestions how to remove the rubber without removing the paint?

This may be a shot in the dark.

With the Motorola 7" VT-71 sets, that gray rubber CRT surround molding will easily be removed with plain water. Have you tried that? The RCA rubber may not be the same rubber type.

But water, in sparse amounts, might work; might not.

This may be a shot in the dark.

With the Motorola 7" VT-71 sets, that gray rubber CRT surround molding will easily be removed with plain water. Have you tried that? The RCA rubber may not be the same rubber type.

But water, in sparse amounts, might work; might not.

The water works! It takes a little soaking but it dissolves the rubber without disturbing the paint!

Thanks for this. Lesson I keep relearning is to try the simplest things first.

You mean the face mask or screen mask.

Shadow mask is an internal part of the CRT behind the phosphor screen used to prevent crosstalk between each phosphor and the 2 guns that shouldn't scan that color of phosphor.

That is a funny slip on my part. I should have called it the mask or the CRT surround. I guess I had crts on my brain.

Thanks.

The water works! It takes a little soaking but it dissolves the rubber without disturbing the paint!

Thanks for this. Lesson I keep relearning is to try the simplest things first.

Excellent.

My CT-100 has a black speck on either the CRT surface or the outer protective faceplate. This is a replacement 15GP22 installed a couple of years ago.

I knew about the speck while installing it but didn't want to risk harming the CRT so I never turned it over to get a good look at the face. I tried wiping it and the inner surface of the protective glass but gave up and thought "I can remove
the outer glass after I've turned the set normal side up". But that failed because its stuck.

Has anybody tried unsticking it from the "rubber" that solidifies and holds it to the cabinet? That is, in a very safe way that won't bother the CRT or break the glass?

I dissolved the rubber with water. The rubber was totally rotten on my set and I ended up removing the coil and putting the picture mask in the bathtub to soak and remove all the gunk.

Mine was goo and after removing the brass trim, I slowly was able to pull the outer glass away. But the black goo mess I think can only be properly removed by taking the picture mask out and soaking it in water.

Finishing off the cabinet. Added the lacquer gold paint. The speaker grill cloth was very dirty and will see if it useable. Is there a replacement available?

Anyhow back to the chassis in the next few days.

That is very nice! Wish your photos were better focused.

That is very nice! Wish your photos were better focused.

So do I! I find the posting of photos on the forum reduces resolution. I think the images may be transcoded from the 3MB original to 300kB. Perhaps the answer is to transcode to 300kB prior to posting?

Has anyone else come across this?

From my experience, I would agree resolution is reduced on this site. Your chassis photos look good. I upload photos from another server and post a link.

It has been a couple of months since I worked on the CT100. Too many diversions made me put this aside for a couple of months. With the onset of winter, I have the chassis back on the bench and have begun the full IF alignment.

The sound IF discriminator alignment was very straightforward. I have just completed the final IF stage sweep alignment and the traps required a minor tweak. The response matches the service data exactly. I am documenting the entire process so there will be more to come on this.

I was proceeding to do the full IF sweep alignment when I made an interesting discovery. The procedure requires applying a -6.0 volts to the IF line and to connect to chassis ground the junction of 2R133 and 2R134. First I see no 2R133 in the v117 (6AN8) plate circuit so assume it was a typo: I see only a 2C133 connected to 2R134.

I am looking forward to examining the chroma and luma channel responses and posting what I see here.

Run into a bit of a snag with the IF alignment.

Lined up the Audio IF and the last (6th) IF stage with no problem. The first IF stage (6U8) located on the tuner I cannot achieve the RCA published response curve. The coupling transformer between the 1st and 2nd IF stage must provide a wide bandpass. I have stagger tuned the primary and secondary in an attempt to secure the best response. the sweep alignment is supposed to include a 6MHz bandpass with a litle dip in the middle. the best I can provide is a hump in the middle with the low frequency end at 41.25MHz elevated above 45.75MHz.

Using the prescribed input head to couple to the mixer diode and from the testpoint through the detector block through T1, the signal is fed to the 6U8 in a common grid amplifier configuration which then is coupled to the grid of the 6U8 pentode section. The output is coupled to the tuner IF output via transformer T2. The detector block is connected to point T2 at the plate of the penthode section of the 6U8 on the diagram. The response curve is not affected by stray capacitance or moving the cables. It is a good consistent trace. I swapped the 6U8 (with NOS 6U8A's) and there is no change.

I am using for the sweep generator an HP8601a and the marker is it's companion HP8600a. The HP equipment is very precise and perfect for television sweep alignment. The swwep alignment of the detector stage matches exactly the picture in the notes.

With the response I achived so far with this coupling, the poor response adversely affects the subsequent sweep alignment from the mixer to the second IF stage as prescribed. Hence I have gone back to investigate further.

My plan next is to pull the tuner top and have a look at the transformer and components around it. The great thing is I may not even have to disconnect any connections as the complete tuner chassis holding the RF amplifier, mixer, oscillator and 1st IF stage is easily removed from the tuner box by removing a few screws.

Curious note: the rest of the curves depict low frequency to the left and high frequency to the right. You would normally get a reversal when the signal is hetrodyned or mixed with a local oscillator with frequency about the desired incoming. In this case no hetrodyning is done so why do the notes show a reversal? I checked Sams notes and they copied the RCA diagram exactly.

Whether you are familiar or not with this tuner, I would appreciate your comments.

Proper alignment will be a big improvement. I’m sorry, but our Westy has a different tuner, but was disassembled and cleaned. Sorry not much more constructive to say.

I haven't done enough TV alignments to offer constructive advice, but...

If you reach a point where you decide you need another CT-100 tuner for parts or to experiment with I somehow ended up with 3 spare CT-100 tuners in my parts stash...

Funny I had to take apart and reassemble the video and sound IF strips on the main chassis and so far there has been no problem there. I took the tuner apart to clean it but did not examine it closely.

Thanks for the offer. I trust the coupling I can fix but it is good to know where to turn if the original unit turns out badly.

This is a real dog to align as it has so many stages.

This evening I found the problem. It was a pretty obvious fault once I started poking around. A decoupling cap was open. I found the fault when I started moving the leads. The 1000pf capacitor was a chassis mount with the capacitor screwed into the chassis.

I could power the tuner portion on the bench while I took measurements. I have replaced the faulty cap with a silver mica cap and the response now matches the RCA notes. And there was a lot more gain!

It earlier worried me that as I changed the signal level the response shape changed. Now I can wind the input level up and down and the response remains the same!

Below are some photos and you can see from my previous post the response matches the published RCA notes exactly.

Further examination of the tuner revealed a second 1000pF capacitor physically separated and open. This bypasses to ground the 6AF4 local oscillator plate return: if it is open, it would likely reduce the oscillator amplitude a frequency marginally.

The third chassis mount 1000pF capacitor looked solid. I noticed the color was green as opposed to the amber faulty ones. Perhaps it was a different batch.

Anyhow, to summarize, it has been essential to run though the RF/IF alignment for any set as the problems would snowball. Besides affecting the luma response by introducing smearing and ringing in the picture, it would drastically affect the I and Q channel responses I plan to examine when I am done the front end.

Proper RF/IF alignment clearly differentiates between the construction costs between late forties RCA sets. Comparing the 721TS which has three IF stages, with an 8T243 or the 8T270 with four IF stages, a proper alignment reveal extra picture detail on later sets. You see the extra detail on the resolution wedge which may be resolved to the center of the pattern and the 721TS ther esolution wedge extending only 2/3 the way down. In this color set which has the the added complication of not only color but the separate chroma difference channel paths.

So this exercise I feel shall be justified by the results i will later find.

Been plodding away at the alignment today. The pages so far is as far as I have gotten so far with successful results.

I am going to back over the entire process and document it. So far I have seen multiple restorations to get the CT100's running but I do not recall seeing anyone doing a full RF/IF alignment?

Has anyone been through this?

Been plodding away at the alignment today. The pages so far is as far as I have gotten so far with successful results.

I am going to back over the entire process and document it. So far I have seen multiple restorations to get the CT100's running but I do not recall seeing anyone doing a full RF/IF alignment?

Has anyone been through this?

Talk to Nick Williams miniman82....He did a full alignment on both his CT-100 and 21CT55 about a decade ago using a B&K 415 and a scope IIRC.

I did a full adjustment of my CT-100. This includes what I seem to remember
as being 88 adjustments, including only one tuner position. Yes, I turned
every knob or pot or coil.

The IF alignment was quite straightforward. I didn't at the time have an accurate marker generator so I tried two methods: zero beating with the
second harmonic of my frequency synthesizer, which only goes to 40 MHz,
or simply picking up stray signal on my AirSpy SDR and setting at the
correct place. The final result matched the spec perfectly. I did not use the Fig. 22 (RCA manual) test head (just coax with hard wired parts with short leads) nor
the Fig 23 IF test block, rather just a 100 mHz scope with 1 megohm input connected by clipping a tiny alligator clip at the end of 4 feet of RG58 to an insulated wire (tack soldered on if necessary) at the appropriate point.

For the RF, I set the oscillator with the Airspy and just tweeked the response
per spec. For my Ch. 39 UHF strip I kludged it using the Airspy and
the harmonic of my sweep generator.

Its all just a lot of adjustments. I still don't quite understand Zenith's snarky
remark "50 adjustments and they all make it worse" as a complement (i.e. it was done right!) or simply saying that too many.

Been plodding away at the alignment today. The pages so far is as far as I have gotten so far with successful results.

I am going to back over the entire process and document it. So far I have seen multiple restorations to get the CT100's running but I do not recall seeing anyone doing a full RF/IF alignment?

Has anyone been through this?


My Westinghouse H840CK15, not a clone of the CT-100, received a full alignment. Here are a few notes and photos of the scope wave forms. The bird photo was just taken November 23, 2022. The restoration was over three years ago. I had to take screenshots to post the 79 MB resolution of about 198 MP of the 15GP22’s 585 K dots. Mike Doyle who is an inactive member here, did the chassis restoration. He worked at Cal Tech developing the Hubble telescope and later helped maintain the Hale telescope at Palomar and taught students at the University.

https://visions4netjournal.com/wp-content/uploads/2022/12/172B2BB2-F8ED-4656-BF4A-1F45CE820782.jpeg

https://visions4netjournal.com/wp-content/uploads/2022/12/E75EBC14-6361-4847-AFC6-2640D3B487BA.jpeg

https://visions4netjournal.com/wp-content/uploads/2022/12/F4715356-EC3E-4D13-91EA-6D8C571161C1.png

https://visions4netjournal.com/wp-content/uploads/2022/12/AF8C3731-D67C-40AF-8E18-4F5876908EC7.png

I have run through the full video and sound IF alignment. I have achieved that has been published.

Note the IF response is flat to 4.2MHz! The chroma response is supposed to be full I to 1.5MHz and Q to 500kHz. The corresponding chroma channels will have a flat frequency response to complement the IF response.

Later sets used the "haystack" response with the color subarrier (42.17MHz) at 50% on the response slope opposite the to the video carrier. This means the chroma channel has a complementary sloping response to provide a flat double sideband +/- 500 kHz bandwidth chroma response.

I am going to go over the entire procedure once again to document and see if I can make more linear the nyquist slope.

I am impressed with the H840CK15. It has 4 IF stages and appears to demodulate the chroma on the R-Y and B-Y axes. This means early on it appeared to be the sensible way forward.

However I question the written statement that the placement of the color subcarrier at the 50% point is on the curve depicted.

Although it is stated that the the color subcarrier (42.17MHz) is at the 50% point on the curve, it looks to me 42.17MHz is at the 100% point. Perhaps teh 50% is instead 41.70MHz?

Excellent work. I’ll go back and check my notes.

I am impressed with the H840CK15. It has 4 IF stages and appears to demodulate the chroma on the R-Y and B-Y axes. This means early on it appeared to be the sensible way forward.

RCA seemed to flop around for a while, trying different schemes. But they settled on R-Y and B-Y, with the CTC-7. I wonder what took them so long, and I wonder if it was more political than technical? After all, RCA was famous for not wanting to be a licensee, and”borrowing” a Westinghouse patent was a no-go. Thus the 4 and 5 were a bit… experimental. Maybe by tge time the 7 came around, they were desperate to get color moving, and gave in?

Also, didn’t Zenith come up with the convergence scheme that ultimately got used by everyone?

(Also, my 4 notes that it uses patens from Phillips. I don’t know what that is about)

The CTC7 and later chassis used the X-Z demod with output matrix/amp/DC restorer stages. Any direct R-Y/B-Y parent would not apply. Plus, it was more stable with tube drift due to the final DC restoration.

The CTC7 and later chassis used the X-Z demod with output matrix/amp/DC restorer stages. Any direct R-Y/B-Y parent would not apply. Plus, it was more stable with tube drift due to the final DC restoration.

I had assumed the earliest sets would have all included I Q demodulators. Interesting that Westinghouse, purported to be the first color set sold, did not employ it.

At the risk of not straying too far off topic, actually the Admiral C1617A was the first with more than 1000 copies made and the Westinghouse H840CK15 was second with approximately 3500 copies made. RCA CT-100 was third with about 4400 copies made.

Admiral was in stores in January, 1954, Westinghouse March, 1954 and RCA April, 1954. Availability of all sets were very limited. As an example, the CT-100 wasn’t available to purchase in NYC until mid May, 1954.

I don’t know what demod scheme Admiral used with their C1617A.

EDIT: Clarification, The RCA could be ordered in April, 1954, but not available until about mid May, 1954.

At the risk of not straying too far off topic, actually the Admiral C1617A was the first with more than 1000 copies made and the Westinghouse H840CK15 was second with approximately 3500 copies made. RCA CT-100 was third with about 4400 copies made.

Admiral was in stores in January, 1954, Westinghouse March, 1954 and RCA April, 1954. Availability of all sets were very limited. As an example, the CT-100 wasn’t available to purchase in NYC until mid May, 1954.

I don’t know what demod scheme Admiral used with their C1617A.

You nerd sniped me on that last line...After a visit to earlytelevision.org I now know it's an I/Q demodulation set.

The GE 15CL100 that IIRC also beat RCA to market is an R-Y/B-Y set with the added weirdness of not having a chroma osc but instead a crystal ringing circuit like a portacolor....The portacolors demodulator comes from a different brand of early color set the 1957-62 Motorola 21CT2.

I now want to read more about what demod circuits the various early color sets had.

A few weeks ago I got out bid on a 21" Raytheon that I happened to have the Sam's for and it's demod was a fairly novel design.

At the risk of drifting the thread a bit more:nono:, we had a GE roundie come in the shop with no color sync. After subbing tubes to no avail, noticed a little Ne-2 neon bulb lurking down in the burst area, and it was lit normally. Figured, change it anyway. Perfect color sync. Never pulled a schematic, but assumed it must be serving as burst gate into the ringy circuit.

The CTC7 and later chassis used the X-Z demod with output matrix/amp/DC restorer stages. Any direct R-Y/B-Y parent would not apply. Plus, it was more stable with tube drift due to the final DC restoration.

So did the CTC5 Deluxe; that one appears to be the first time RCA used the X-Z scheme. The demodulation angle, according to the RCA service data, is 57.5°. That got played around with in later chassis using the FBP/FJP CRTs due to the all sulfide phosphors those tubes used in an attempt to get subjectively correct color rendition from CRTs that no longer conformed to NTSC specs.

Precisely.
They also used a simple RC phase shifter to get the desired angle, so no quadrature alignment was needed.
If you compare phase shift components year to year, you can see just when they adjusted the angles.

The NTSC color space was never truly adopted due to the very saturated primaries and low luminesce from television receivers of that period.

I have been looking forward to the Christmas break to pick up on the CT100. The rest of the family have been sick (not me and my wife) so we have postponed family gatherings this year.

Have completed two run throughs of the IF/RF and Chroma Bandpass alignments and testing. Subsequent run throughs of the procedure yielded some improvements in an attempt to get better frequency responses. I had spent many hours on this starting in late fall bringing me to this culmination point.

To achieve a flat topped wide IF response is the challenge especially with a stagger tuned amplifier with 6 stages! The video IF alignment of the CT100 require you to first sweep the 6th IF to 2nd detector stage followed by the 1st IF stage on the tuner followed by the first 2nd IF stage (first stage on the main chassis. Then the 3rd, 4th and 5th stages are peak aligned to 44.9MHz, 42.9MHz and 41.3MHz respectively. The final overall sweep requires you to adjust the 3rd, 4th and 5th to achieve the full 4.1 MHz bandwidth flat topped response. I could not achieve the response without tweaking the other stages. I feel it important to restrict the final response tweak to the three stages so experimentation was required to understand and determine where the discrepancy occurs. I found the problem with too much gain around the video carrier (45.75MHz) by very slightly altering the 2nd IF tuning higher in frequency to bring the whole respnse in line.

The luminance channel response with all traps and the chroma channel bandpass responses fell niceling in line with the RCA documentation. I had problems however with the I and Q channel responses. Recall all of the white peaking coils were open and I could not repair them.

I managed to wind myself replacements which worked fairly well. Q Channel 6.7mH coil I altered from a ferrite core 33mH coil only to find the the Q response diminished sharply after 100kHz. I ended up winding about 500 turns of AWG44 wire on a 1.0 Megohm 1W brown resistor which gave me the correct 500kHz response.

The I channel with the coils I provided peaked too sharply at 1.0 MHz. I found an old NOS Meissner 1.0 mH coil shunted with a 10K resistor which yielded the response I desired.

A frequency sweep from the 1st Video amplifier input to the kinescope grids did produce the response published.

Here are a few more photos including the published notes photos.

For for the IF and baseband bandpass alignment, I used the combination HP8601a RF Sweep Generator with HP8600a Digital Marker. The HP 8601a sweep rand is from 100kHz to 110 MHz.

For the complete VHF Tuner alignment from Channel 2 to 13, I used a Wavetek Model 1050 Sweep Generator with the HP8601a as the Frequency Marker. For Channel 13 marking, the HP8601a second harmonic was easily seen.

(The HP 8601a goes up to only110MHz and the second harmonic of 105.6 MHz is 211.25 MHz which is the video carrier on channel 13).

As my scope has a 100MHz bandwidth, I did not feel necessary the demodulator probe suggested by the RCA notes. Hence my snapshots show the un-demodulated or un-rectified carrier frequency sweeps.

I managed to wind myself replacements which worked fairly well. Q Channel 6.7mH coil I altered from a ferrite core 33mH coil only to find the the Q response diminished sharly after 100kHz. I ended up winding about 500 turns of AWG44 wire on a 1.0 Megohm 1W brown resistor which gave me the correct 500kHz response.



Thanks for that info.

Found something similar.

When L42 is replaced with ferrite, the Chroma Reference Osc Control is unstable.

A Miller 4624 will work. Even a pair of series connected Miller 5220's works.

Thanks for that info.

Found something similar.

When L42 is replaced with ferrite, the Chroma Reference Osc Control is unstable.

A Miller 4624 will work. Even a pair of series connected Miller 5220's works.

Curious. I will have to research this further how perhaps the ferrite affects the "Q".

With the initial RF-IF-baseband channel alignment done (including setting traps. Last week while checking the I channel I traced a self oscillation to an open 20uF chasis mount capacitor. I had on hand an NOS triple 20uF 450v which I replaced. (The rest of the original chassis mount electrolytics are original after reforming and checking for leakage. I must have missed the one that was totally open).

All testing so far has been minus CRT. Time now to next test the chassis connected to the 15GP22. Using a set top box, I had scoped good video up to the CRT grids. The sweep circuits were good and there was good high voltage available to feed the convergence, focus and second anode connections.

I managed to get a stable picture with lots of brightness and good contrast. I noticed the Keyed AGC is a bit wonky and need to investigate this. After this setting up colour demodulation, purity and convergence.

The 15GP22 seems to have very good emission. The tube is a rebuild: are the bright filaments normal?

I have been looking forward to the Christmas break to pick up on the CT100. The rest of the family have been sick (not me and my wife) so we have postponed family gatherings this year.

Have completed two run throughs of the IF/RF and Chroma Bandpass alignments and testing. Subsequent run throughs of the procedure yielded some improvements in an atempt to get better frequency responses. I had spent many hours on this starting in late fall bringing me to this culmination point.



I commend you on those plots. They are truly top notch.

I commend you on those plots. They are truly top notch.

Thanks.

Want to tackle the chroma demodulators. But did purity convergence and gray scale next.

I found it difficult to get a consistent grey scale. I find when I advance the brightness and contrast beyond a certain point, a high luminance level (towards white) causes the picture to go out of focus and the raster expands suggest poor HV regulation. Need to look at the HV rectifier...

What is the technique to get a good consistent grayscale?

Good grayscale???

Answer: CONSERVATISM and a dark room.

You need a dual probe scope that can subtract. I have a pile
of Tektronixs that do fine.

Attach probes to the CRT red grid and any CRT cathode (i.e. either side
of Sam's R284.) Scope in subtract mode so you measure the grid to cathode voltage.

Adjust for a good picture, not very bright, well below blooming or other "obvious"
problems. The image you are looking at needs lots of both full black and
full white, and preferably full red too.

When you turn up either contrast or brightness you will note double clipping of the red.
and thus compression.

The DC restorer clips one extreme and the CRT itself clips the other. Turn up
the contrast too much and they BOTH clip. You want to avoid this like the plague,
its bad for the CRT and makes the picture turn cyan.

So what I did was to make up little arrows out of red and blue masking tape.
I set the contrast and brightness at the middle of the "usual" range and attached
a blue arrow to both knobs, pointing up. I then turned up the contrast to just
below the double clipping point and attached a red arrow to it.
i returned the contrast to the blue arrow and turned the brightness to the double
clipping point and attached a red arrow to its knob.

So, when adjusting the set, if you DO set one knob above the red arrow, you
need to set the other one below the blue arrow by an appropriate amount.

I also added blue arrows to hue, color, and tone.


You could also attach the scope across R284 and set the arrows so you never
get (dc) current flow (you will of course get spikes at sharp edges.)

One other note: at constant line voltage, my settings for these have remained
correct for three years now! Never Twice the Same Color is simply wrong.

Thanks for the wealth of information. I was earlier pondering why the focus and HV supplies were drooping on video high average luma level scenes. I suppose it was driving the tube to hard. Everything settles down if you back off the contrast.

The set otherwise appears healthy apart from one odd anomaly: when powering up, after about 40 seconds the sounds comes up and you hear the characteristic HV crackle. The picture is initially low contrast. About after two minutes the contrast comes up. It is as if one tube in the video chain is extra slow warming. When testing the tubes, the emission was good and I have replaced many (most) of the tubes.

Any thoughts?

You could do the 7 second test, pull one tube in the video chain while it's warmed up, plug it back in 7 seconds later and see if contrast returns fast or slow and repeat till you find your culprit or through all possible tubes that could cause it.



I have to commend you for actually listing the parts you used for the peaking coils...Other brilliant minds here have gone through the same effort without listing part numbers, and only giving a vague notion of the brand and the process with their specific test equipment, so someone without the right gear can't duicate their results.
It's good to teach the process, but it's also important to explain the results of the process so others can check the work, and benefit from it.

I guess that these sets were used in a rather dim room and that was normal. When I worked for E.J. Korvette, (1966-1967) color sets were in a special room and the light was dim. I have a CTC-9 in queue and I must remember this when I finish restoring it. I do have a raster so far!

You could do the 7 second test, pull one tube in the video chain while it's warmed up, plug it back in 7 seconds later and see if contrast returns fast or slow and repeat till you find your culprit or through all possible tubes that could cause it.

After starting pulling tubes and plugging them in and not finding the culprit, I decided to try this: I measured the AGC line bias when it was operating okay. It measured about minus 15 volts. I put my bias box across the AGC line, set it to -15 volts and then switched on the set. The picture popped up normally as I would have expected as the high voltage appeared. I swapped the 6AN8 AGC keyer tube and no change. Something is amiss with the AGC.

I will put the scope to the circuit tomorrow.

Spent much of yesterday determined to solve the AGC problem. AGC was wonky:picture would appear about a minute late and if you advanced the AGC control and returned it, you would enter picture overload and it would not recover unless you detuned.

Checked the waveforms (courtesy of the Sams notes) fror AGC keyer in and keyer plate and was correct.

I had changed the paper capacitors and checking resistors, the 4.7 Mohm resistor (used for agc delay) was open. After replacing the resistor, the AGC system slowly oscillated between overload and positive video.

As it is a closed loop system, tried checking tubes. After about four hours, it occurred to me to check the AGC line for wiring. Recall the IF section was badly rusted due the mouse inhabitants. I finally discovered a little choke feeding AGC voltage to the 2nd IF stage open! It was affected by the mouse urine and had earlier tested okay after I cleaned it and reinstalled it. The corroded leads broke of as I removed it a second time. So I performed an autopy on it and in the process found it was simply a winding of a single layer of AWG 44 wire. I took a 1 Mohm 1/2w resistor and made replacement holding the resistor in a variable speed Ryobi power drill.

Installed the choke and AGC worked properly and as it should.

There was a happy side benefit to all this: I checked again the IF response due to the added choke. Went through the full sweep alignment in an hour as outlined in the RCA instructions. Recall from my earlier postI had to make addition tweaks to stages to minimize a bump in the response around the video carrier? Wekl that annoying bump disappeared after the choke fix. The RCA instructions said you only need to slightly tweak T109, T110 and T111 (third fourth and fifth IF stage bifilar transformers) to get the proper response. Sure enough, the final oberall sweep was very close and as RCA prescribed, only those three transformers needed minor tweaks to get a good response!

I have included pictures of the chokes and the set as it is now performing.

Some off air pictures.

Some off air pictures.

It doesn't get much better than that. I would submit to you that only a few left the factory displaying a picture that good. Maybe I am wrong.

Great detective work!

Those pics look super! White balance and purity look about perfect. Can you capture some pics from an old favorite source like The Wizard of Oz?

Looks much improved from the previous shots. You’re well on your way. Congrats on bringing another CT100 back to life.

Spent a bit of time on the set tonight. It is working well. Issues are fairly minor. Here is a rundown of the good vs bad points.

The Good:
1. Repeated the full IF sweep alignment. This was to ensure each preliminary stage of the IF alignment fell into place so that the final overall sweep alignment only required minor adjustments. Succeeded with only having to make minor tweaks to get the proper response. With the entire RF - IF alignment, chroma bandpass and demodulators complete and successful peaking coil replacements for the luma, I and Q channels, the picture is nice and sharp with no ringing.
2. Convergence very good. Better than I had expected with the electrostatic convergence.

The Bad:
1. Cannot get as good purity as I think it should. Could not get rid of a green contamination in the lower right raster. I removed the chassis to demagnetized as best I could with a degaussing coil to no avail. Was able to conceal it with compromises.
2. AGC problem. Although I fixed the open choke, the AGC still provides "bi-stable" operation. Set starts up okay. However, if you interrupt the signal briefly and reapply, the the AGC voltage drops to zero and the video overloads. By detuning with the fine tuning control and retuning the picture returns. The problem disappears if I remove the AGC delay 4.7Mohm resistor (between AGC line and B plus). Checked all components and wiring. (Recall I had to disassemble the IF chassis to remove the heavy rusting).
3. 15GP22 socket intermittent. The red dropped out this evening. Checked okay the voltages for the red gun at the tube socket. Flexed slightly the socket and the red returned. Suspect it is the Red Screen pin 4 connection which is iffy. I earlier cleaned a rebuilt the CRT socket on the set. The 20 pin plug on the tube it looks like a large chunk of the socket previously broke away and the previous set minder reconstructed it with an epoxy resin. Appears they used a mould for the resin and was well done. However it would be nice to put a good original socket on it. Does anyone know if there are any available?

I hooked up the DVD player and played the prerequisite Wizard of Oz...

Coming along nicely!

Quote: Spent a bit of time on the set tonight. It is working well. Issues are fairly minor. Here is a rundown of the good vs bad points.

comments interspersed:

The Good:
1.
2. Convergence very good. Better than I had expected with the electrostatic convergence.

IF you adjust adjustments 82-88 (of 88!) carefully you can get almost perfect convergence. These are the tilts and translations of the yoke.


The Bad:
1. Cannot get as good purity as I think it should.

My first CRT, now gassy, had great convergence. My current one has
a bit of red in two places that I just can't get rid of. Its really very minor,
even on a B&W picture.


2. AGC problem.

I had the exact same thing. Simple cure: since you are running on a
local modulator, signal is too strong. Install a pad right at the set terminals. I have a cheapie balun followed by a balanced 300 ohm pi-pad made from 1/2 watt resistors. That instantly cured this infuriating problem. Signal to noise is still essentially perfect. I recall that my uncle, in 1954, had the exact
same problem ... he lived 3/4 mile from the tower!
But it was already known, since his huge B&W set had the same pad necessary. So does my Hallicrafter's 7 inch set. Other sets work fine with the huge signal.

3. 15GP22 socket intermittent.

I had the same problem on a filament terminal. I got a replacement socket from the ETF but did not use it ... I just carefully bent the contact a tiny bit
in the original socket. The replacement would work, but its not the same constrution and would need some machine shop work to be reliable.

I hooked up the DVD player and played the prerequisite Wizard of Oz...

Very nice images! My opinion only, looks to lack a bit of contrast, can you adjust? I know this is subjective.

Try contacting Steve McVoy at the Early Television Foundation. I received one for my 15GP22.

EDIT: I’m sure the images are much better than the camera captured.

Very nice images! My opinion only, looks to lack a bit of contrast, can you adjust? I know this is subjective.
...
EDIT: I’m sure the images are much better than the camera captured.

Ditto.

I think black level ("Brightness" control) is a tad high in these photos - an easy adjustment. Things like this can happen if you adjust the set with room lights on and then turn them off to take pics or vice versa. If the brightness control is at minimum, it would indicate that CRT bias voltages need some adjustment.

Also want to suggest taking the time to get the camera lined up dead center to avoid perspective distortion.

Ditto.

I think black level ("Brightness" control) is a tad high in these photos - an easy adjustment. Things like this can happen if you adjust the set with room lights on and then turn them off to take pics or vice versa. If the brightness control is at minimum, it would indicate that CRT bias voltages need some adjustment.

Also want to suggest taking the time to get the camera lined up dead center to avoid perspective distortion.

Blame it on an impatient photographer! I was busy with other things and did not spend sufficient time grabbing snapshots.

To digress a little bit, I am impressed with the setup procedure of the CT100 however. Because the matrixing is external from the CRT and R, G and B are DC restored immediately before the signals are applied to their respective grids, the setup was simple and effective:
1. Set Color Control to minimum. With brightness control maximum and contrast control minimum, adjust screen controls for a barely viable gray raster.
2. With a bright image, adjust blue/ green gain for white highlights.
3. Adjust blue/background controls for gray in low levels.

I found after this adjustment, the resultant brightness range was ample and correct and the grayscale very good.

Further digressing, with good DC restoration I feel I now have a better understanding why later monochrome sets had little or no DC restoration. With blacks firmly clamped, if the CRT limited beam current and/or high voltage supply is not up to reproducing high average picture luminance, picture blooming results.

This and other CT100s I have seen appear very susceptible to this. You may set to haved good overall contrast and brightness on an average picture when a bright overall scene will cause the image to bloom out of focus and disappear. Watching in a darkened room with lowered brightness and contrast is fine.

It is amusing to reflect on a an article I saw in "Wired" regarding the anniversary of the launch of the CT100. It included a republished current (1954) review of the CT100 and the reviewer complained about the soft and fuzzy picture. No doubt in comparison with a bright 21" monochrome set of the same period, the viewing of the CT100 must have been in less than ideal conditions with the brightness and contrast too far advanced!

I am glad therefore I have the opportunity here to reduce rather than increase the brightness (black level).

2. AGC problem.

I had the exact same thing. Simple cure: since you are running on a
local modulator, signal is too strong. Install a pad right at the set terminals. I have a cheapie balun followed by a balanced 300 ohm pi-pad made from 1/2 watt resistors. That instantly cured this infuriating problem. Signal to noise is still essentially perfect. I recall that my uncle, in 1954, had the exact
same problem ...

That was it! I attenuated the RF by using a 6 way splitter and that fixed the problem. I remain curious why the AGC latches? Obviously the heavy overload which prevents the keyer from generating a negative voltage but is fine once recovered. I see that an additional 0.1 ufd following a 680kohm resistor feeds AGC beyond the IF line. This means upon the sudden application of higher than normal RF, the IF AGC line will react faster than the RF AGC because of the additional low pass filter. Meaning the RF amplifier may go into heavy overload and not recover.

Removing the 4.7 Mohm AGC delay resistor alleviates the problem at the expense of lowered S/N. (As if that is a problem nowadays). Perhaps lifting the 0.1 ufd would fix this?

I am not going to bother since simply attenuating the signal was the fix. Very appreciative of this tidbit of information.

And than to both of you for the 15GP22 socket tip.

Further digressing, with good DC restoration I feel I now have a better understanding why later monochrome sets had little or no DC restoration. With blacks firmly clamped, if the CRT limited beam current and/or high voltage supply is not up to reproducing high average picture luminance, picture blooming results.
.

I think it actually is something else. One: cheapness. Two: customer complaints about dark pictures.

Look carefully at both the CT-100 DC restorer circuit and the results on screen.
It does not do full DC restoration .. by intent! Its, if I remember rightly,
somewhere between 75 and 85%. This produces a bit extra brightness on
dark scenes, which the customers actually liked better. In fact, **I** still like it better, even in my dark room.

Of course, back in the day at least for live TV ... there were no dark pictures! Producers made sure that their shows didn't have any, and TV stations avoided black screens like the plaque. I supposed telecined movies did get dark scenes through though.

I think it actually is something else. One: cheapness. Two: customer complaints about dark pictures.

Look carefully at both the CT-100 DC restorer circuit and the results on screen.
It does not do full DC restoration .. by intent! Its, if I remember rightly,
somewhere between 75 and 85%. This produces a bit extra brightness on
dark scenes, which the customers actually liked better. In fact, **I** still like it better, even in my dark room.

Of course, back in the day at least for live TV ... there were no dark pictures! Producers made sure that their shows didn't have any, and TV stations avoided black screens like the plaque. I supposed telecined movies did get dark scenes through though.

ISTR some soap (dark shadows?) from the 50s had black backgrounds and would illuminate the characters and maybe the table they were sitting at to make it look like they were floating in the void.

Look carefully at both the CT-100 DC restorer circuit and the results on screen.
It does not do full DC restoration .. by intent! Its, if I remember rightly,
somewhere between 75 and 85%. This produces a bit extra brightness on
dark scenes, which the customers actually liked better. In fact, **I** still like it better, even in my dark room.


The CT100 DC restorer discharge path is 1M ohm, and the charge path looks like about 10K ohm, which appears to be 99% DC restored to me.
I stand ready to be corrected if someone can detail how this circuit could produce only 85% restoration.

Later sets with luma drive to the cathodes typically had deliberate ~85% DC coupling, which Consumer Reports complained about for years. Later solid state sets, especially those with video analog ICs and auto tracking, had 100% DC restoration, which stopped the complaints.

The CTC-5 super chassis (the cost-cutting disaster) had less than 100% DC coupling in the color difference outputs also, resulting in reduced saturation in an all-red image, for example. This was probably done to reduce tracking shift when replacing demodulator tubes.

In the early days, the limited dynamic range of the gamma correction in the camera, combined with some judicious black clipping, combined with the limited contrast of reflective CRT screens, could be and was used to produce the "subject in front of black void" effect. There were some puppet performances on TV (like acts on the Ed Sullivan show) where the puppeteers were in scene but covered in black, and the video engineers just clipped them out of existence.

This became much less possible with the advent of Plumbicon cameras with wide dynamic range including gamma correction down into the shadows. Current solid state cameras for HD and cinema have made the shadows even more clearly visible.

I saw a talk online by a well known cinematographer who said that with film they had figured out the lighting and exposure to give the director either visibility or invisibility in the shadows, but with current digital cinema cameras, they always see into the shadows. They tell the director what he wants to hear, and then achieve the desired effect in post production.

This was illustrated in the live NBC production of Sound of Music, where they had a transition from one location (set) to another by actually dollying the camera through a door with a dark surround; but instead of seeing a black void surround, you could make out details of the studio/set wall.

The CT100 DC restorer discharge path is 1M ohm, and the charge path looks like about 10K ohm, which appears to be 99% DC restored to me.
I stand ready to be corrected if someone can detail how this circuit could produce only 85% restoration.


I'm actually not quite sure. I thought about it a lot and never decided.
What I report is what I measured with a 32 megohm resistive (and proper compensation capacitor) scope probe.

I think is some sort of combination of the presence of sync pulses and setup
in the signal and the presence of added blanking pulses.

But what I AM sure about, Consumer Reports notwithstanding, is that
with the brightness level of early CRTs, consumers did and should have complained about not seeing dark pictures well with 100% restoration.

Same thing applies to photos: I print some of my photos in a way designed
to be viewed in direct full sunlight. People ooooh and aaaaah about these when displayed properly ... but complain if viewed at "official museum light levels". That needs different (dodge and burn) processing. Such processing is clearly visible in sports programming in modern TV. Look at white parts of uniforms in direct sunlight.

Note on the TK-41 image orthicon color cameras:
The gamma correction was a three-linear-segment approximation to a power curve, so it was definitely too shallow at the dark end to compensate for the real CRT power curve, resulting in compressed shadow contrast. Also, it approximated a gamma of 1.7 instead of the nominal gamma of 2.2, resulting in increased contrast and color saturation. This was the same trick as applied in earlier color reproduction processes like color photography and printing, but resulted in exposure level being critical, with set design color selection needing a restricted contrast range for pleasant results, and the occasional appearance of bright white shirts as somewhat fluorescent and glowing. White clothing sometimes was dyed light gray to compensate, or performers would sometimes wear light blue shirts.

I'm actually not quite sure. I thought about it a lot and never decided.
What I report is what I measured with a 32 megohm resistive (and proper compensation capacitor) scope probe.

...

Same thing applies to photos: I print some of my photos in a way designed
to be viewed in direct full sunlight. People ooooh and aaaaah about these when displayed properly ... but compain if viewed at "official museum light levels". That needs different (dodge and burn) processing. Such processing is clearly visible in sports programming in modern TV. Look at white parts of uniforms in direct sunlight.

Thanks - measurement trumps theoretical guessing, but my visual impression of CT-100s I have seen is that the restoration is much better than the 85% of later sets. On the other hand, I may not have been looking at a good selection of source material for this.
...
Comparison of monitor images and prints is a constant problem. With the fixed monitor calibration I use, prints can look too dark in dim room light and too bright in the competition viewing booth, so I do have to process differently. Monitors have been introduced that compensate for room brightness according to some psychophysical model - we'll have to see how well that works as time goes by.

In the early days, the limited dynamic range of the gamma correction in the camera, combined with some judicious black clipping, combined with the limited contrast of reflective CRT screens, could be and was used to produce the "subject in front of black void" effect. There were some puppet performances on TV (like acts on the Ed Sullivan show) where the puppeteers were in scene but covered in black, and the video engineers just clipped them out of existence.

This became much less possible with the advent of Plumbicon cameras with wide dynamic range including gamma correction down into the shadows. Current solid state cameras for HD and cinema have made the shadows even more clearly visible.

I saw a talk online by a well known cinematographer who said that with film they had figured out the lighting and exposure to give the director either visibility or invisibility in the shadows, but with current digital cinema cameras, they always see into the shadows. They tell the director what he wants to hear, and then achieve the desired effect in post production.

This was illustrated in the live NBC production of Sound of Music, where they had a transition from one location (set) to another by actually dollying the camera through a door with a dark surround; but instead of seeing a black void surround, you could make out details of the studio/set wall.


This subject is interesting. I don’t know if you have watched recent highly touted movies in the past few years that are of interest to this viewer, but there seems to be a trend with flat, very dark, low color content films. I read that this is the desire of the Director who wants to set a moody foreboding atmosphere. The new Bladerunner movie was particularly disappointing along with a recent chain of movies with dark, almost colorless scenes throughout. I may be wrong, but is this an excuse for Directors to use this trend as shortcuts in cinematography? I’ve spent hard earned money to purchase equipment capable of bring out the best in films. It’s not my equipment to blame, it’s important to me that all is properly set up and calibrated. A few movies come to mind, “Mama Mia Here We Go Again”, Brigerton are noteable stunning exceptions and others.

I want to see well calibrated color and excellent shadow detail in movies and content.

I hope we will see additional screenshots from this set. Particularly shot in a darkened room, with the image filling in the entire field of view.

This subject is interesting. I don’t know if you have watched recent highly touted movies in the past few years that are of interest to this viewer, but there seems to be a trend with flat, very dark, low color content films. ...

Preceded by the cyan/orange look, a fad and crutch for lack of real creativity in most cases. It's never a green/magenta look, because that is too unacceptable as a possible range of natural lighting color.

As far as dark scenes go, having the action mostly invisible most of the time seems stupid to me. Brief clips of unrecognizable motion to convey the frenzy of a scene are fine, but they live by contrast with the recognizable parts as far as I am concerned.

With the excellent contrast range of LCD and other current displays, the content can have dim but recognizable scenes for night, just as movies could be dark for night scenes in an unlit theater. This was not possible with a CRT in a normally lit room, so good practice was to brighten the dark scenes when transferring to video.

I recall clearly when local stations would run 16mm copies of movies that had no such adjustment. The dark scene of a train in the night was reduced to seeing only the round circle of the headlight, and multiple fading ghosts of it as well due to the lag of the vidicon film chain.

For a while, Kodak provided a special color print film that had a deliberate contrast-reducing fog in the shadows. It looked washed out to the naked eye, but reducing the black level in the telecine brought the contrast back to normal while reducing lag and loss of shadow detail.

This thread about brightness got me off my duff (combined, I might add, with a
fake bomb scare that kept me away from the office) to check if something
in my set's setup had changed to make for dimmer pictures. And since checking
requires a scope, I checked the DC restoration, at least on the red.

It turns out that my occasional tweeks of the gray scale had got my marks
for the brightness control a bit off, but every other adjustment
was spot on. Fixing the "normal" settings gives a picture that is 100% watchable
on a day like today ... overcast but with the window shades open.

And yes, the DC restoration is in the 85 to 90% range. That's measuring how much the sync tip level
at the red grid changes divided by difference in grid voltage between full white screen and
deepest black blanking.

When my set was first working it did bloom, but now it never ever does. I
don't know why. It could be the parts replacements in the HV section, including
regulating the focus voltage with a string of Zeners. Or it could have been
the setting of the range of the brightness control. I'll never know.

This thread about brightness got me off my duff (combined, I might add, with a
fake bomb scare that kept me away from the office) to check if something
in my set's setup had changed to make for dimmer pictures. And since checking
requires a scope, I checked the DC restoration, at least on the red.

It turns out that my occasional tweeks of the gray scale had got my marks
for the brightness control a bit off, but every other adjustment
was spot on. Fixing the "normal" settings gives a picture that is 100% watchable
on a day like today ... overcast but with the window shades open.

And yes, the DC restoration is in the 85 to 90% range. That's measuring how much the sync tip level
at the red grid changes divided by difference in grid voltage between full white screen and
deepest black blanking.

When my set was first working it did bloom, but now it never ever does. I
don't know why. It could be the parts replacements in the HV section, including
regulating the focus voltage with a string of Zeners. Or it could have been
the setting of the range of the brightness control. I'll never know.

Sounds like you have it nailed, post a few current screenshots.

Sounds like you have it nailed, post a few current screenshots.

No need to post more screen shots. I've posted plenty. The current ones
would be identical to the last ones.

That includes my avatar, which was taken on an earlier CRT. The original
file is bluish.

Sorry for the silence. Other projects have been going and I wanted to think through some of the issues. New photos will follow soon.

If you recall the speaker was badly rusted. I took it apart cleaned it and reassembled it. It works fine except that it appears to have lost some of it's sensitiveness. I tested by substitution another speaker and suspect the problem is the pemanent magnet is not as strong as it was. I am looking for a local substitute.

The AGC overload latching problem: Recall with the RF modulator fed straight to the CT100, the RF/IF amplifiers would tend to latch in overload. The CT100 performed better following the suggestion to attenuate the RF signal. Studying the circuit, I have pondered the value and placement of the 4.7Mohm resistor. With six stages of ampligication, the video level at the 2nd detector is approximately 7 volts p-p. There is a lot of gain and the 4.7Mohm resistor was intended to positively add to the AGC line to no doubt improve S/N performance. My contention is that the major noise contributor would be the RF stage. So I wonder why the resistor is situated prior to 1R132 (560kohm)? Certainly moving it to the point indicated by the arrow will delay application of the AGC voltage until after the the IF stages have been applied sufficient negative bias to prevent overload.

2R176 (4.7Mohm) should be raised to at least 10Mohm or more if it is moved to prevent front end overload. Alternatively, removing the 4.7Mohm resistor altogether demonstrated that with full signal, the agc cicuit appeared to work better with no overload latching. I want to compare S/N in each situation.

I suppose this is less of an issue now that the analog broadcasts are no longer around. It will be a purely academic investigation.

The HV power supply wilting: when attempting to advance the brightness control results in peak white pictures blooming and going out of focus. I tried monitoring both Brightness and Focus voltages as the average brightness level rises. Both the nominal 5000volts focus and 19000volts second anode take a dive. This suggests the flyback supply is not up to the job of maintaing a constant voltage as the beam current demand increases. Is this normal or is there a fault which affects efficiency?

Other than that, I see quite a bit of pincushioning of the image.I would attribute this tithe geometry of the 15GP22: The display panel inside the tube is very flat hence the scanning radius will induce pincushioning. Not a fault. I only mention this as an observation.

Couple of thoughts.
I think modern signal feeds into your CT100 might cause overload compared to the old analog days of 1954 and perhaps the set was designed in this way.

Would like to see a photo of the pincushingion effect for comparison purposes.

The blooming and out of focus with high brightness happens on my set as well. I have heard it mentioned before by others and I noticed it on one of the sets at the ETF museum also, so it is not unique to your set.