Another RCA CT-100 discovery B8001599

[dtvmcdonald]

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.

[Penthode]

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.

[Penthode]

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.

[Penthode]

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.

[old_tv_nut]

Great! Keep the reports coming.

[kvflyer]

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.

[Penthode]

Originally Posted by kvflyer

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.

[consoleguy67]

Very good, meticulous work.

[kvflyer]

"Mo Bettah"! Looks great.

[Popester]

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

[Tom9589]

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?

[Yamamaya42]

Originally Posted by Tom9589

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?

[Penthode]

Originally Posted by Yamamaya42

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.

[dtvmcdonald]

"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.

[Penthode]

Originally Posted by dtvmcdonald

"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.