Here are the first pictures!

The small pics have been uploaded for immediate viewing, for the large file right click/save as on the URLs below. WARNING: picture files are large, 3+mb. Expect long load times.

http://miniman82.4t.com/images/prototype%20color%20set/IMGP4529.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4530.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4531.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4532.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4533.JPG

5 more.

http://miniman82.4t.com/images/prototype%20color%20set/IMGP4534.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4535.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4536.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4537.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4538.JPG

5 more.


http://miniman82.4t.com/images/prototype%20color%20set/IMGP4539.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4540.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4541.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4542.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4543.JPG

Last 5.

http://miniman82.4t.com/images/prototype%20color%20set/IMGP4545.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4546.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4547.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4548.JPG
http://miniman82.4t.com/images/prototype%20color%20set/IMGP4549.JPG

I did not realize that you bought that set. Congrats! Looks like it will be a fun project! Looks like lots of electrolytic cans in there.

Better'n Christmas when you were 5 yrs old...(grin)

First thoughts:

It's obvious they were trying different things with this chassis; there are holes where parts should be, disconnected parts, and it has a generally unkempt look to it. Wires are routed in a military fashion, tied off and specifically placed. Some circuits like deflection and tuner/front end look like standard fair. Others are a complete mystery- I see no evidence of what would be a dead givaway as a standard looking delay line, but there is an empty spot on the underside of the chassis marked 'delay' (see pic IMGP4543.JPG).

The HV section is strange- there is a 6CD6 output in one of the sockets (the ST shaped one in image IMGP4536.JPG), but then there's also a 6BQ6 in the socket right next to it. No idea what that's about. Damper tube is a 6W4GT, which seems like it should be the incorrect tube for a color set. Most sets use 6AU4GT(A), so I'm not sure what to think there. HV rectifier is a 1B3, which again seems like small B&W style stuff. Color sets typically use higher rated tubes like 3B2 or 3A3. Same thing with focus rect, which is a 1V2 where most color sets use a higher rated tube such as 1X2B.

Picture tube is developmental C-73547, similar to the one at the ETF. Getters look strange to me, I think the tube might have gone to air since one of them is clear in the center. Either that, or they were too close to the glass at the time they were flashed and scorched the glass- I've seen that before on audio output tubes. Other than that, everything else looks pretty good. I now have the monumental task of figuring out how exactly this thing works, and to that end I will be focusing my efforts on the color section first. Bob Galanter has said he will try and stop by this weekend to have a look at it, and I'm hoping Mark will stop by with his tube tester.

Much more to come, stay tuned! :thmbsp:

Very exciting! Are you going to draw a schematic of what is there?

Phil Nelson

I might not have to, Ed Reitan has told me he may have a schematic from the early chassis somewhere in his library. I just need to wait and see what exactly this thing is, and we'll move on from there.

Nick, first, thanks for all the great hi-res photos. I am not sure when the 6AU4 was introduced, but this set may perdate its introduction. I have production 15" color sets with 1B3s in them, so it is not unheard of. Probably hard on the poor 1B3s, but they work.

You are probably planning to do this, but I suggest you make a tube chart, listing tupe type/mfg/date code. Also, a list of part numbers on all transformers, as these often contain date codes and manufacturer info.

It is anybody's guess if the CRT is still under adequate vacuum to operate, but the signs are encouraging. Of course, my Hawkeye rebuilt 15GP22 tests good, had beautiful getters, and lights up purple like a neon tube when voltages are applied! So you just can't tell by looking.

Do you have the missing tubes, or are these going to be part of the mystery? I don't see tube numbers marked anywhere.

Are any of the control labels readable? I can't tell from the photos.

This a a fantastic set, thanks for sharing. I look forward to your upcoming discoveries.

:drool:Wow!:jawdrop:

Holy schmit, you are really gobbleing up some ultra-cool rare stuff lately. Your not trying to compete with the ETF, are you?;):naughty::scratch2:

Hope you can get it to run. If that happens you might just have the earliest working single CRT non-mechanical color set.:thmbsp:

Either way it should be a very interesting restoration.

Good luck!

Tom C.
PS: Now I know what the festive ocasion was, and wow that is one impressive ocaision.

Nick, first, thanks for all the great hi-res photos. I am not sure when the 6AU4 was introduced, but this set may perdate its introduction. I have production 15" color sets with 1B3s in them, so it is not unheard of. Probably hard on the poor 1B3s, but they work.


You're welcome, John! At some point I should probably stitch them together to make one giant one, though it would take a long time to download. I don't know when the 6AU4 came out either, but I know we had previously speculated on the horizontal output tube- the 6CD6 in this chassis is dated the 17th week of 1951! Most of the rest of them date from '50/'52, with the 1B3 in the HV section showing 1958.

You are probably planning to do this, but I suggest you make a tube chart, listing tupe type/mfg/date code. Also, a list of part numbers on all transformers, as these often contain date codes and manufacturer info.


Yes, it's one of the things on my list. A lot of the parts on this chassis show RCA stamps, so I'm fairly certain this was made by them. Vert output transformer, power supply choke, some of the other RF cans, and of course the tuner are all RCA items along with some of the tubes (assuming those are the tubes it's supposed to have).

It is anybody's guess if the CRT is still under adequate vacuum to operate, but the signs are encouraging. Of course, my Hawkeye rebuilt 15GP22 tests good, had beautiful getters, and lights up purple like a neon tube when voltages are applied! So you just can't tell by looking.


Of course, you are correct. I hope the test this weekend brings good news. I can look through the center of the base, and am able to see a slight patch of green around the evacuation stem which indicates copper corrosion. I hope it has not done any harm.


Do you have the missing tubes, or are these going to be part of the mystery? I don't see tube numbers marked anywhere.

It's currently missing 2 tubes, no idea what they are or what they do. Part of the mystery! Perhaps Ed Reitan can shed some light on it?


Are any of the control labels readable? I can't tell from the photos.

Yep! The labels are faded, but I can still see what they say. Written in pencil on the front of the chassis going left to right are:

horizontal/vertical hold, power switch/volume, contrast/brightness, and tuner.

On the back:

Pretty much the same stuff as a CT-100 would have. Purity, convergence, drives, backgrounds, focus, ect. Nothing that would make me say "a-ha!", but I don't know much else about the set at this point anyway.

After following some wires from the CRT socket, it quickly became apparent that there are 3 tubes (6BL7's) that are driving pins 3, 8 and 18 on the CRT socket (which would be grids on a 15GP22). I assume that means these are the adders or some part of the matrix, but the strange thing is there are also 3 diodes on terminal strips for each one as well. They look like the same type of thing that always seems to get used as a detector in IF strips. DC resto, perhaps?

I thought the getters looked a little small on that tube too. But it was never meant to live a long life, just test set. I think the same about the 1b3's in later daily use they proved unsatisfactory for color sets. Good luck with it and many thanks for the cool picts!

John: Almost missed it, but there's a control in the center of the chassis. It's only marked with a 'C', so I assume it's the color control.

WOW .. this is going to be the most amazing thread... this is real history .... I sure hope you can get the set to come alive... this really is what all this is about. Good luck and congratulations!

Congratulations on getting to delivered. It should be an exciting project.

The space marked Delay doesn't look like it is in the video section?

Nick,

Great photos. Glad everything arrived in good order. My money is still on this being an RCA prototype. Look forward to what ever you guys discover.

-Steve D.

Glad it all got there in good shape Nick. Especially that rare proto CRT. Hard to tell what the getter looks like from the photo, but you could check for continuity on the filiments before I get there on Saturday.

I will bring the Sencor and the B&K along with the adapter for the 20Pin bi-decal base.

From the photo I can tell the gun assembly is definately of the 15GP22 type with electrostatic convergence cup. It has some centering wings that are spot welded to the cup that are not present on a 15G gun but other than that, the gun is a 15G gun.

In the event the crt is a leaker, You could send it to France to be leak sealed with frit glass and re-gunned. John and I will be sending our first 4 15G tubes over there sometime in august. We have special cartons and a crate being built. Each round trip shipment to France and back will contain 4 tubes.

Good for you Nick. Will enjoy watching your progress. That is quite the set.
Greg

Congratulations for your acquiring this unique set, Nick. I notice the convergence pin on the CRT socket looks like new, so it must not have had much use, though the 1958 1B3 is interesting.

John and I will be sending our first 4 15G tubes over there sometime in august. We have special cartons and a crate being built. Each round trip shipment to France and back will contain 4 tubes.
Bob-

I am happy to hear that the RACS 15GP22 rebuild project is moving beyond the one-off stage and into true production.

One of the things that Harry Poster told me was that he suspected that the previous owner (not a TV person) had plugged tubes in sockets just to sell the set.

Bob, one of the photos from Harry showed the filaments glowing, so the filament has continuity and the tube isn't fully air.

The chassis seems to show signs of a normal life and maintenance period during your set's first years in some kind of service. Sprague and Mallory single-section electrolytics and the 1B3 date coded 1958, all suggest a period of "normal" use.
Having no apparent delay line along with a chassis area earmarked "delay" is another unsolved mystery.
I gather reading twixt the lines that this set recently came from Harry Poster. He sure has had some rare merchandise through the years.

The adventure begins! Have you determined at all if this could be a dot-sequential prototype rather than early NTSC?

The chassis seems to show signs of a normal life and maintenance period during your set's first years in some kind of service. Sprague and Mallory single-section electrolytics and the 1B3 date coded 1958, all suggest a period of "normal" use.
Having no apparent delay line along with a chassis area earmarked "delay" is another unsolved mystery.
I gather reading twixt the lines that this set recently came from Harry Poster. He sure has had some rare merchandise through the years.

You know, a luminance delay line can also be a network of peaking coils and resistors in a can, or a long thin shielded wire wrapped around a non-inductive core with an active frequency compensation circuit. Until cheap glass delay lines were developed there were several methods of delaying a broadband signal. - Of course the delay might have been removed.. :sigh: I gather this set does not use IQ demodulation otherwise it would need TWO delays.

This is kinda like findin' Gottlieb Daimler's heretofore unknown SECOND prototype of his 1886 car under a tarp in a dry barn somewhere...

I notice the convergence pin on the CRT socket looks like new, so it must not have had much use.

I think you might be right....

:banana::banana::banana::banana::banana:


Took a little time to wake up, but all 3 guns read at the top of the good scale after sitting for 5 minutes and the life test ain't bad either. Anyone wanna hear how the variac powerup of the chassis went? :scratch2:

Anyone wanna hear how the variac powerup of the chassis went? :scratch2:You guys are getting all the fun! Don't keep us in suspense...

I think you might be right....

:banana::banana::banana::banana::banana:


Took a little time to wake up, but all 3 guns read at the top of the good scale after sitting for 5 minutes and the life test ain't bad either. Anyone wanna hear how the variac powerup of the chassis went? :scratch2:

You're got to be kidding, this tube tested good!! :thmbsp::thmbsp:
Can it be plugged into a working CT-100 chassis to see if it works.

so is the face of that tube a greyish or a little greenish in color. More like the color of the early 15GP's or more the color of the 21axp's? I wonder if the 1b3's meant the tube was designed to have lower beam current. Too bad there ain't a Sam's you could order for that chassis.

You're got to be kidding, this tube tested good!! :thmbsp::thmbsp:
Can it be plugged into a working CT-100 chassis to see if it works.

Still can't be sure until HV or tesla coil present; the getter is a bit worrisome.
But if there's no faint blue neon glow anywhere along guns (viewed in dark) with tube tester, that would be promising.

From what I learned by using the CR-70, a tube with air will peg the needle after advancing the cutoff control beyond a certain point. You reach the ionization point of the gas inside, and then you get full conduction. Exactly that happened with the 21AXP22 that was in my Director 21, purple neck to boot. But this one is fully variable throughout it's entire range, and the needle rises slowly as it warms up just like it should. So I'm optimistic about it, but we won't know until some HV can be applied.

so is the face of that tube a greyish or a little greenish in color. More like the color of the early 15GP's or more the color of the 21axp's?

It looks greenish to me, kinda like the 21AXP22 in my CTC-2B. I have it parked right next to the CTC-4 at the moment, and it's very obvious the difference when viewed right on. The screen on the 2B almost glitters, while the one in the 4 just looks like plain paper.

This is real history if only the 6-bolt CRT is functioning.

I think the next question is not if this set can be made operational but IF it should be.

If it's an RCA Prototype it truly is a signifigant piece of history, replacing capacitors and other components would seriously compromise it's historical value IMO.

I think there's historical value in being able to see just what a dot-sequential or proto-NTSC electronic receiver was capable of. We've now been able to see what the CBS sets were capable of for quite a few years, but when they first came back to life it was quite a revelation.

I have mixed feelings about whether to restore it and I can think of good arguments for both sides.

Personally, I would find it hard to resist making it work. It was designed as something to be used, after all, not a museum piece.

I would soothe my conscience by doing nothing invasive, restuffing paper caps as well as electrolytics, maybe even finding resistors that look more period-correct. Ideally, when it was done, it would look the same (at least to a casual eye) but WORK as the designers intended.

Just my $0.02.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I agree with Phill's suggestion for how to go about electronically restoring it.
Better to keep it looking original if you restore it IMHO.

Tom C.

Anyone wanna hear how the variac powerup of the chassis went?
If you do get a matching or near-matching schematic diagram from Ed Reitan, you may be able to do just that after some electrolytic restuffing. Absent that schematic, you could draw your own (got a few days or weeks?) and compare it to the CTC2 schematic to maybe narrow down the missing or incorrect tubes.

Either this forum or my browser needs to be taught some of the words we use around here. It doesn't like variac, powerup, or restuffing.

The adventure begins! Have you determined at all if this could be a dot-sequential prototype rather than early NTSC? I wondered that too. Based upon a reading of Wentworth and Fink plus the preponderance of 1952 tubes, I don't see now how it could be a dot sequential set using three-state communitator circuitry. However, I couldn't resolve one way or the other their flirtation with phase alternation in that time period. So, it probably uses equaband quadrature circuitry for chroma, bypassed luma (of course), in 1952 perhaps a nonstandard color subcarrier frequency, and maybe PAL-like circuits.

My two cents.

Pete

If it were mine, I'd want to restore it to working condition using reliable modern capacitors. Save the removed parts.
But, I would take multiple high resolution detailed digital photos of the entire chassis as documentation history of the set.

You are now part of this TV's history.

Carl

Do you have any information about where this TV has been over the last 60 years?

Carl

I wondered that too. Based upon a reading of Wentworth and Fink plus the preponderance of 1952 tubes, I don't see now how it could be a dot sequential set using three-state communitator circuitry. However, I couldn't resolve one way or the other their flirtation with phase alternation in that time period. So, it probably uses equaband quadrature circuitry for chroma, bypassed luma (of course), in 1952 perhaps a nonstandard color subcarrier frequency, and maybe PAL-like circuits.

My two cents.

Pete

But it appears that the set has been used over the years http://www.videokarma.org/showpost.php?p=3006198&postcount=24 So it was either built as 3.579 quadrature, or has been modified to be NTSC-compatible.

I really doubt if the set was used over the years. The only evidence of that is the tube date codes, which is tenuous. I don't see any other components that look newer than 1952 ish.

Congratulations on having what appears to be a working tube.

Congratulations on buying this ultra rare prototype colour TV set, I am glad to see it has gone to a good home and to someone of these forums!!! :D Best of luck getting this set crankin again and I look forward to seeing your progress along the way!

I may have missed it, but what's the story of how you got this set in the first place? Inquiring minds want to know :)

I may have missed it, but what's the story of how you got this set in the first place? Inquiring minds want to know :)


It was at auction, on Ebay. I would like to know how Harry Poster got a hold of it though, he never did tell anyone unless I missed it.

I think the next question is not if this set can be made operational but IF it should be. If it's an RCA Prototype it truly is a signifigant piece of history, replacing capacitors and other components would seriously compromise it's historical value IMO.


Here's my take:

It is a museum worthy piece, therefore it belongs in a museum. For that reason, I am considering placing it at the ETF once I am done with it.

I have always been of the mind that if the set actually works, no one is going to care what's 'under the hood', since 9 times out of 10 it would not have worked on original capacitors anyway. No one walks into the ETF and says about the Model 5: "you know that thing would be much better non-functioning and with original caps". I don't think so. It's a much better thing to see it in operation, it blows away any thought of keeping it original once you see something on screen.

Lastly, I may not have to change anything in the first place. The chassis has what appear to be aerospace grade metal-film capacitors, so it may not need total replacement of the caps. They are not prone to leakage and breakdown like wax/PIOs are, so we'll see if they are any good. The lytics will be restuffed, but thankfully they are all mounted on wafers and secured to the chassis with screws. They will be easy to do.

But it appears that the set has been used over the years http://www.videokarma.org/showpost.php?p=3006198&postcount=24 So it was either built as 3.579 quadrature, or has been modified to be NTSC-compatible.

I use the popular version of Occam's Razor: Don't allow an unproven variable to screw up a comfortable conclusion.:D

As Steve McVoy indicated, there are competing reasons for a post-1952 tube to be in this set. Also, as been stated earlier in this thread, there is not a scintilla of visible evidence that the CRT socket had 4-or-so kV on the convergence element (pin 13) for an extended period.

Still, there are no final conclusions. Perhaps this chassis will turn out to be from Hazeltine Corp.; they were located in the same general area as RCA Labs and where Harry Poster now has his business.

The quest goes on...

Pete

Harry told me he got the set from a picker, and and it probably came from the Camden area, but he didn't know anything else about it.

Here's my take:

It is a museum worthy piece, therefore it belongs in a museum. For that reason, I am considering placing it at the ETF once I am done with it.

I have always been of the mind that if the set actually works, no one is going to care what's 'under the hood', since 9 times out of 10 it would not have worked on original capacitors anyway. No one walks into the ETF and says about the Model 5: "you know that thing would be much better non-functioning and with original caps". I don't think so. It's a much better thing to see it in operation, it blows away any thought of keeping it original once you see something on screen.

Lastly, I may not have to change anything in the first place. The chassis has what appear to be aerospace grade metal-film capacitors, so it may not need total replacement of the caps. They are not prone to leakage and breakdown like wax/PIOs are, so we'll see if they are any good. The lytics will be restuffed, but thankfully they are all mounted on wafers and secured to the chassis with screws. They will be easy to do.

Hi Nick,
Congratulations! I agree with your statements one-hundred percent.
Also, once you have an operational platform, Pete might consider performing comparitive colorimetry measurements on your CRT.

Looks to me like there is one newer yellow electrolytic soldered under the chassis.
I'm a big fan of getting rid of all the leaky paper caps. But I have also had very good
luck with electrolyics in cans from the pre-wars up thru the mid 50's. I just reform them with a very low charge current and they are not leaky. It is not like they are in a place to cause a lot of damage when they short. My TRK-120 has all of it's original electrolytics and it works fine.. I thought Harry told me he got it from a picker from the Lancaster area.. I'll have to go back and check my emails.

I've been back tonight snooping again through your excellent and detailed photos of your chassis. I found it very interesting that the rear apron red, green and blue screen controls (presumably) have plastic color keyed shafts. That seems almost prophetic in such an early prototype.
For a chassis this seminal, I'd have expected three generic pots, identical in every way, both physically and electrically.

Looks to me like there is one newer yellow electrolytic soldered under the chassis.
I'm a big fan of getting rid of all the leaky paper caps. But I have also had very good
luck with electrolyics in cans from the pre-wars up thru the mid 50's. I just reform them with a very low charge current and they are not leaky. It is not like they are in a place to cause a lot of damage when they short. My TRK-120 has all of it's original electrolytics and it works fine.. I thought Harry told me he got it from a picker from the Lancaster area.. I'll have to go back and check my emails.

I also remember the Lancaster area being mentioned in an early post or e-mail on this.

-Steve D.

My mistake. Lancaster is what Harry said, but he wasn't certain.

My mistake. Lancaster is what Harry said, but he wasn't certain.

Steve,

Either city would work. RCA had plants in both Lancaster, Pa. and Camden, N.J.

-Steve D.

Working under a blank check from Sarnoff, engineers developed the tri-color, shadow mask prototypes and finally the 15GP22 in Lancaster I believe. I once owned a wonderful RCA booklet about RCA's tri-color CRT development project. I lent it on request to the late Rudolphus (?) Swan, a retired engineer from Sylvania's tube division who, despite repeated requests, never would returned it.

Several requests have been received for me to label the back panel controls, so here it is!

Since there does not seem to be any main power transformer or power rectifiers present, is the 7 pin male plug on the lower left chassis back panel where a separate power chassis plugs in?

Perhaps the two pin male plug is a power on/off circuit to allow the TV chassis to remotely control the power chassis? And the is two pin socket above it a convenience power outlet to plug your VTVM in?

Since there does not seem to be any main power transformer or power rectifiers present, is the 7 pin male plug on the lower left chassis back panel where a separate power chassis plugs in?

Most likely, since the early prototypes had a lower chassis which supplied power to the whole shebang.

Perhaps the two pin male plug is a power on/off circuit to allow the TV chassis to remotely control the power chassis? And the is two pin socket above it a convenience power outlet to plug your VTVM in?


I looked at the 2 pin thing, and it's wired into the heaters of all the tubes with some really thick wire. I suppose it's possible that the heater circuit is the 2-pin, and the rest is B+ type stuff on the 7-pin one.

There are some pictures, by Harry Poster, of an RCA prototype set that looks like this set showing the CRT mounted. It even shows the black tape. Link: http://www.earlytelevision.org/rca_color_prototype.html

I looked at the 2 pin thing, and it's wired into the heaters of all the tubes with some really thick wire. I suppose it's possible that the heater circuit is the 2-pin, and the rest is B+ type stuff on the 7-pin one.

So you don't actually have the power supply for this set? Did it go missing? And won't that slow down getting it going?

It should be possible to make a replacement power chassis. If a schematic could be found it would help.

It should be possible to make a replacement power chassis. If a schematic could be found it would help.

However that puts to rest the question of whether to recap it or leave in non-working survivor condition. The whole bottom chassis is going to be all-new.

So you don't actually have the power supply for this set? Did it go missing? And won't that slow down getting it going?


No, and there's no reason to expect it will ever turn up. No one knows where it is, so it is assumed missing. Something like that would be very common looking anyway, so it probably was either tossed or repurposed for something else. It won't really slow anything down, other than the time it takes to build a new one. It's easy to trace the wiring, and figure out what voltages need to go where. I figure I'll start with an old console amp chassis, install a suitably large power transformer, and use the sockets for the rectifiers. Maggie chassis are plentiful, so that's what I'll probably use. That, or I'll strip the old organ chassis in the next room.

Found the heater string connections: the 'main' part of the chassis, that is, everything that is not tuner/IF related, gets it's 6.3 volts from the small male 2-prong plug on the back. The tuner/IF strip is powered from pins 1 and 6 of the 7-pin round plug, with pin 1 connected to chassis ground.

That reminds me: I'm gonna need like 30 tube shields! lol

I've got a box of maybe ten or fifteen assorted 7 and 9 pin tube shields your welcome to.
I've also got an old power supply from a corespondence course that you can have if it will help.
http://i1095.photobucket.com/albums/i469/ElectronicMemory/DSCN0829.jpg
Tom C.

Hey my dad took that same course! I remember playing with that PS when I was a kid!
Its no good for that tv, its going to need to be more current and they'll have to figure out what different voltages are needed too. That PS is for single tube circuits.

Most likely they are going to have to come close to matching the specs on the PS for the ct-100's that some of those guys already have access to, or possibly a model 5, something like that. This tv should have a lot of very similar circuits to what later became the production version of this set.

Anyway it should be fun for these guys, and for us to read about. Thanks guys!

Harry told me he got the set from a picker
That reminds me of visiting a well known radio dealer years ago. His place was packed with amazing items. I finally broke down and asked, "Where do you find all this stuff?" He shrugged and replied, "People bring things to me."

Phil Nelson

There are some pictures, by Harry Poster, of an RCA prototype set that looks like this set showing the CRT mounted. It even shows the black tape. Link: http://www.earlytelevision.org/rca_color_prototype.html
Isn't that interesting? Is the CRT serial number a match to your prototype, Nick?

Harry offered the set to the museum before he put it on Ebay. I tried to get him to donate it and take a tax deduction, but he declined.

Isn't that interesting? Is the CRT serial number a match to your prototype, Nick?

They are one and the same.

Despite my misgivings about tampering with this set I very much want to see it operating again :yes::yes:
No point in letting it sit around until the CRT finally goes to air and is useless.

Thinking about the historical importance of this thing is inspiring, Every one of the billions of CRT based Color sets in the world can trace it's DNA back to this set (along with the few other RCA Prototypes).

One more idea, if the tube is gunned the same as a 15GP22 perhaps it would be a good idea to hook it up to a CT-100 chassis and see if it'll actually light up?
If nothing else it would be an interesting glimpse of the Phosphors used.

It's an idea I've tossed around a few times, trust me. I don't have a CTC-2 chassis though, only CTC-2B.

It's an idea I've tossed around a few times, trust me. I don't have a CTC-2 chassis though, only CTC-2B. Okay, let's work this out. I just got back from Detroit area where I picked up Bob's 1948 Moto; are you two still getting together tomorrow? (just tried calling Bob. no answer). I can probably stuff my CTC2 and the Moto in the Yaris. I for one am itching to see that tube light up w/Dorothy. What say you?

Pete

If the Italians can restore DaVinci's Last Supper fresco in Milan and justify it, this box o' bulbs can get the same. Go for it. The intellectual and historic end result is seeing the intent and accuracy of the artists work...not how it got there. Think of the glowing phosphors as the canvas of the fresco and the restored, tinted plaster as the chassis.

I think intent on the part of the inventors/designers applies here. Just think of how many changes they made to this particular chassis to get what they wanted. It was not a one and done effort. And there is no hope of picking one particular version of this set. They were all failures until it worked. It was an ongoing process to get the CRT to glow in color and that should be the same here and stop at that point.

If the Italians can restore DaVinci's Last Supper fresco in Milan and justify it, this box o' bulbs can get the same. Go for it. The intellectual and historic end result is seeing the intent and accuracy of the artists work...not how it got there. Think of the glowing phosphors as the canvas of the fresco and the restored, tinted plaster as the chassis.


I for one have to agree, especially since I have seen said fresco in person :smoke:

If this is going to happen, Pete and Bob will stop by on Sat and we'll see what the result is. My hope is that we will all see what RCA had in store for the viewing public back in 1952-ish!



I think intent on the part of the inventors/designers applies here. Just think of how many changes they made to this particular chassis to get what they wanted. It was not a one and done effort. And there is no hope of picking one particular version of this set. They were all failures until it worked. It was an ongoing process to get the CRT to glow in color, and that should be the same here and stop at that point.

Agreed, though there should be one caveat: the developmental chassis was an experiment in what was to be, insomuchas color chassis go. Let's not make any assumtions on what was TO COME, based on what we already know. That would be a mistake. Every evolutionary step beyond what I currently own is still a grand mystery. Nothing is written in stone. That said, I eagerly await the results of a developmental CRT powered by a production CTC-2 chassis. Much fanfare waiting in the wings!

This is really, really exciting. :yes:

Interesting thing about this chassis is it may not have ever worked, at least not in the fashion we have come to expect from a Color TV.
You may get green people and orange skies for all we know, maybe it won't produce any kind of stable colors at all.

Maybe red apples, green grapes and blue bananas. :)

Actually it all poses a question ..if it was an experimental chassis... one designed to have changes and additions made as RCA made changes to its dot sequential system.... just which version do you restore the set to match?

But this whole exercise is one of the most exciting on this forum ever!

Throwing in my two cents; I'd restore it the way you plan on doing it, if the CRT is actually good. If it were bad, I'd have to think hard before having the CRT rebuilt. As Eric said, we don't know how functional the chassis ever was. But, it would be fun to find out.

John

:banana::banana::banana::banana:


IT WORKS!!!!



:banana::banana::banana::banana:


Bob and Pete stopped by today with a CTC-2 chassis, wooden CRT truck, extension cables, CRT testers (to read all the guns at one time), and of course a Wiz of Oz DVD in tow. One more test of the tube with Bob's Beltron proved that all 3 guns were indeed working perfectly, so we set about powering it in a real world situation with Pete's CTC-2. The CRT was placed in the truck, cleaned, yoke and purity assemblies installed, and Bob's anode extension wire attached. We connected my DVD player to the CTC-2 using Pete's composite input mod box, and powered the chassis through my RCA Isotap variable isolation transformer set to 115 VAC.

We threw the switch, HV spooled up, and got a bright full raster! There were a few hiccups getting an actual picture to appear which were mainly my fault for powering the DVD player incorrectly, but in the end we were able to get something on the screen. Something was amiss with the Merrill though, as it was only powering one gun at a time and so we were not able to do any convergence or get a color picture. Just proving the tube still works was a monumental success for the comminuty, and so we called it a day.

Enjoy the pictures!

Setting up the CRT for testing.

http://videokarma.org/attachment.php?attachmentid=170757&d=1308454284

Historic first light!

http://videokarma.org/attachment.php?attachmentid=170758&d=1308454284

Initial images being displayed. It's supposed to be the yellow brick road, but degaussing, purity, and convergence all still need to be done before anything decent appears on this tube.

http://videokarma.org/attachment.php?attachmentid=170759&d=1308454284
http://videokarma.org/attachment.php?attachmentid=170760&d=1308454284
http://videokarma.org/attachment.php?attachmentid=170761&d=1308454284

What incredible news! :banana::banana::banana::banana::banana::banana:

Congratulations!
jr

Oh guys ..this just so amazing ..what a find ..now you can really set out on that Yellow Brick Road... where this journey will end is anyone's guess!!

As far as convergence & purity are concerned, are you sure that the CTC-2 chassis and this developmental CRT are fully compatible with each other?

Wow, an almost 60 year old prototype CRT in pristine condiition actually working! It will really be something if the chassis can be made operational and get a picture. Congratulations! I wonder if the prototypes used the same phosphors as the CT100's.

As far as convergence & purity are concerned, are you sure that the CTC-2 chassis and this developmental CRT are fully compatible with each other?


Yes, if they were not we would not have had a decent monochrome picture on the screen. The electron gun is almost identical to a 15GP22, the pins are all the same. At this point we were not able to get color because of a chassis fault, and even if the chassis was 100% the tube needed to be degaussed and we didn't have the degausser. Therefore, we could not do any of the setup operations which would be required for proper display. A project for another day.

RCA may have dropped the ball by going with the leak prone 15G, this design seems more robust.
I wonder what their reasons were, perhaps we'll find out.

Eric H, I don't think so. I have four (4) metal bell prototype color CRTs, and they are ALL down to air, and I know of several others that are also down to air. So this is the only one still under vacuum. Certainly no better than the 15GP22, and probably worse, though the data sample is rather small, hard to draw meaningful statistical conclusions.

This is fascinating, to see that early CRT working. Is it a metal-cone design? Can any of you see possible places where leakage could happen (on this tube, or the other prototypes)?

If you're going to draw statistical conclusions from the types of envelopes used, it would seem more accurate to include such tubes as the 12UP4, 16GP4, 19AP4, and 21AXP22 since it's basically the same thing as this one contruction wise. So far as I know, the 15GP22 was the only one to use that infamous flange seal. *EDIT: actually I think the CBS 205 and Westinghouse tubes used a similar design.*

Now I'm not saying that welding the CRT together was a particularly good idea no matter how it's done, but it seems to me that there are probably more operational tubes with the prototype's kind of construction than there are operational 15GP22's though there were also more of the B&W ones made.

Yabba-dabba-doo! I was hoping to see pictures.

Phil Nelson

Possible Leaks in Metal Cone portotype color CRTs

1. Evacuation seal (copper pinch off type)
2. Wire to glass seals at base (not very likely)
3. Glass to metal seal at faceplate of tube
4. Glass to metal seal between neck and rear of metal funnel
5. 8 welded bolt heads which protrude through sides of metal bell, part of the phosphor dot plate and shadow mask mounting assembly
6. Metal to metal weld between front and back of metal funnel (similar to 21AXP22)

Summary: Lots of places for these tubes to leak!

I had the honor of seeing this historic event in person. I just happened to be there today to purchase some sets, and stayed to see if the prototype CRT would light. I figured I was going to miss the power up of the CRT so I did not bring my camera, but got some shots on the cell phone. If I can figure out how to get them off of the phone I'll post them, and email them to miniman82 as promised. I wish I had the presence of mind to bring my degaussing coil.
I even got some pictures of the set with the green beter converged than on the first moments of it displaying video.

This is definitly the most historic TV related event I've ever attended, and perhaps the most historic event I'll ever attend!!!

What an amazing experience to be among the few to see perhaps the only working original prototype shadowmask color tube display picture for the first time in several decades!

I'm still amazed that I got to see that in person!

Tom C.

Possible Leaks in Metal Cone portotype color CRTs

1. Evacuation seal (copper pinch off type)
2. Wire to glass seals at base (not very likely)
3. Glass to metal seal at faceplate of tube
4. Glass to metal seal between neck and rear of metal funnel
5. 8 welded bolt heads which protrude through sides of metal bell, part of the phosphor dot plate and shadow mask mounting assembly
6. Metal to metal weld between front and back of metal funnel (similar to 21AXP22)

Summary: Lots of places for these tubes to leak!

Now this has me worried. The picture on the 21AXP22 in my Admiral 29Z1 (C322C16) was pretty dim years ago. I stupidly tried flashing the cathode, but that made no difference. I'm now wondering if the tube was indeed going soft. It needs a few tubes put back in and capacitor replacements before I can try it again. If the sulfide tube IS shot at least I have a NIB 21FJP22 to replace it with.. but those rich reds will be gone.

I had a 1981 Sony XBR in which the picture tube went completely to air after 8 years. At $700 in 1990 dollars for a replacement that was the end of it.

This is a fascinaitng thread. Thank You.

My experience is that the 21AXP22 is much less likely to leak. We have 8 tubes, either in sets or in boxes, and none have leaked. You'd never have that luck with 15Gs.

My experience is that the 21AXP22 is much less likely to leak. We have 8 tubes, either in sets or in boxes, and none have leaked. You'd never have that luck with 15Gs.

Good, that encourages me to get this set going again, thank you. :banana:

The heavy duty (D550?) Weller soldering guns double very effectively as a degaussing coil.
Try it, you'll be amazed.

The heavy duty (D550?) Weller soldering guns double very effectively as a degaussing coil.
Try it, you'll be amazed.

We tried my my antique Weller 145/220 watt, it didn't do anything at all. I'll get my degaussing coil back from Mark sooner or later, don't worry.

This is really, really exciting. :yes:
Roger that. This thing's got a Lost Ark mystique about it, in spades. oc

As far as convergence & purity are concerned, are you sure that the CTC-2 chassis and this developmental CRT are fully compatible with each other?

It's Pete Deksnis here at Bob and Tamy's house for an overnight visit. Mal, it's a good question and I believe based only on physical shape, the two are not compatible. As to adjustments for purity are concerned, no, I wasn't about to shift that CT-100 yoke back and forth along the neck with 20 kV 1/2-in. from my hand. I did rotate the purity coil and it did affect the picture somewhat, but this was not the time for perfection... too many variables at play.

My CTC2 had been powered up for the first time yesterday since breaking down the RACS 15GP22 rebuild demo at ETF on May 1; since then it traveled over 1500 miles in the back of my Yaris, so I was very glad to see the HV still working (including the ozone if you were there seeing and smelling it operating at ETF!) and only the green channel not operational.

Glad to have been able to inspect the proto chassis up close; still many, many questions to resolve. Nick and Bob found a socket for a crystal, but there's no positive indication that it is for 3.579595 mc.

What a great opportunity we few had to participate in and witnesss such an historic event.

Pete

Fantastic work Nick, Pete, and Bob! I'm really glad you guys were able to get to "First-Light 2011" in such a short period of time.

it's a good question and I believe based only on physical shape, the two are not compatible.

Correct. I was speaking more to the electrical compatability between the 2, and they seem to be a perfect match. Bob noted that the gun was almost identical to a production 15GP22 one, only a few added supports differ between them.

Wouldn't it be nice if you could lay hands on the engineering notes for your prototype? Delay line questions, burst frequency, convergence supply specifications, how and if high voltage is regulated, what tubes go where, the list seems endless.
It looks as if this thread could last a while. That's perfectly fine by me.:yes:

My guess is that all these questions will be answered by our color experts as Nick traces the circuits.

Yes, the schematic is the thing.

To the Color Gang,

Nick and I have just had a wonderful 1 1/2 hours on the phone tracing his chassis circuits from the CRT grids back through the 6BL7 color crt drivers,and 6AS6 demodulators. We had discussed the evolution of NTSC standards, back through the Feb. 2, 1953 NTSC Field Test Specification, and further back to the initial definition of the NTSC field test standard published on November 26, 1951. See http://novia.net/~ereitan/NTSC_overview.html

This November 26, 1951 standard used quadrature modulation of 1 MHz. B-Y and R-Y color difference signals, CPA (Color Phase Alteration), a 3.898125 MHz. subcarrier, and reference burst on a pedestal on the back porch of horizontal blanking. . In doing our tracing Nick discovered a transformer labeled "CPA".

Our initial conclusion is that it is a chassis probably used during the CPA Field Testing during 1952. There were several manufacturers who built field test receivers during that period.

We have yet found nothing to confirm that it was built by RCA or by any other manufacturer.

The chassis may have been modified from CPA up to the later NTSC Feb. 2, 1953 standard. We will see.

Further tracing of the circuit and documenting the circuits will be don.

Ed Reitan

Very interesting indeed!

Thank you Ed for the revealing and informative conversation, the amount of information that the early color crowd is providing is astounding to say the least. The collective knowledge shared here cannot be found anywhere else on planet Earth, of that much I am certain and I am forever grateful!

As Ed indicated, we started out following the wires though the various components connecting each stage to the previous one. I was poking around in an area that I had assumed would have something to do with demodulation, positioned in the circuit just prior to the 6BL7 grid driver tubes, and containing 6AS6 tubes. That's when I struck gold: Hidden under some passive components was a chassis stamp in black ink right under a tall transformer, which reads CPA.

http://videokarma.org/attachment.php?attachmentid=170764&d=1308519977

It's a pretty tall can, so I was curious what it had inside. Taking much care not to damage or disturb anything, I slowly removed the nuts holding it to the chassis and this is what's inside. It's only about half the total height of the can, and appears to be some sort of transformer. I cannot see any kind of slug in the center of it, so I'm assuming it's an air core non-adjustable type.

http://videokarma.org/attachment.php?attachmentid=170765&d=1308520089
http://videokarma.org/attachment.php?attachmentid=170766&d=1308520089
http://videokarma.org/attachment.php?attachmentid=170767&d=1308520089

The chassis may have been modified from CPA up to the later NTSC Feb. 2, 1953 standard.
Ed Reitan

From Pete Deksnis @ Bob's place: I had the same thought; but I suspect the transformation was not completed; hopefully so, as it would simplify the reverse engineering.

Pete

Nick... Amazing set!

Wow! This is all very fascinating, will be watching this thread with great interest...:yes:

This get's more interesting by the day! Probably one of the most interesting things that's happened here yet.

The genesis of Color TV being uncovered before our eyes, it's one thing to read about field tests and demonstrations for the FCC, quite another thing to see the actual hardware rediscovered and brought to life.

It's only been 60 years since this was being created but so much seems to have been lost.

I suppose it's lucky there's as much written documentation as there is, I wish there was a few hundred hours of period Technicolor footage to go with it.

They must have filmed some of their tests??

To go back in time with a HD Flip Camera hidden in my pocket.

Do you guys know if this set was EVER actually fully functional ?

Do you guys know if this set was EVER actually fully functional ?

<shrugs>

At some point it probably did, but being a test bed of sorts it seems to have been in a constant state of change since day one. I wouldn't be the least bit surprized if upon power application the horizontal and HV section started spooling up, same thing goes for vertical deflection. The real mystery here is how does it handle color, and how do we get that color image to appear on the developmental CRT?

This is waaaay cool!

That's effin' amazing Nick! too bad I was so busy this weekend! I'da loved to see that light up for the first time in person! That tube looks like it could have a great picture on it once a chassis is set up right for it. I think your money was wisely spent on this piece of history.:yes: Now, if that chassis can be made operational, I think people will be knocking on your door from states away to see it work!

That's effin' amazing Nick! too bad I was so busy this weekend! I'da loved to see that light up for the first time in person!


It was a good day for color TV history, but don't worry there will be other opportunities in the future to view this one in the flesh. My hope is to have the entire thing ready and working for next years ETF, but we have a lot of work in front of us to get to that point.


That tube looks like it could have a great picture on it once a chassis is set up right for it. I think your money was wisely spent on this piece of history. :yes: Now, if that chassis can be made operational, I think people will be knocking on your door from states away to see it work!


That could be, Pete already drove 5 hours to see it! :smoke:

If I can't make it to next years ETF for whatever reason, a video will be made to show the masses in the banquet hall. Probably be a good idea to have something better than my Handycam to take the pictures with, though.

1. Hello. What’s in there?

2.
Out of the box comes a C73547.

3. Beltron test of C73547.

4. Here Bob is checking numbers discovered on the tube rim. I found them while cleaning dust and grit from the tube. They were hand-punched, obviously before final assembly. It is unclear what they represent.

5. Only seconds after first raster.

Pete

6. Overall CRT light-up configuration.

7. Another view showing, in better perspective, the location of the 15GP22-based yoke on the C73547 neck. We were mindful of the 20 kV covering the bell and being so close to the yoke. The purity coil is positioned on the neck based upon the proper location for a 15GP22 installation. In this flash shot the screen is washed out, but there’s Dorothy shining through!

8. Nick and Tom, who’s gotta be the luckiest vintage TV devotee on the planet, enjoying some Wizard of Oz footage on the C73547.

9. Who was there? Seven people witnessed the event. Tom (Electronic M), his Dad, his Mom, Bob Galanter, Nick Williams, his wife, and Pete Deksnis. The ladies it seems quickly turned their attention to more pressing discussions. After the hi-fives, I called John Folsom in Florida (that's his cradle the CRT is resting on). A bit later, Ed Reitan and John Folsom were on a conference call with Nick.

Pete

Great stuff Pete,

That's what you want to see when you test a tube. Simply incredible.

Thanks for posting,
-Steve D.

This just has to be one of those .... oh my gosh!!! moments!!!

I'm keeping up to date with this thread skim reading the main parts and looking at the pics and I am so impressed with the progress made with this set in such a short time!!! :D It is totally amazing to see that the picture tube is excellent and displaying a picture and I look forward to seeing colour pictures on this tube once you get the prototype chassis up and running with the tube mounted in and configured to display colour pictures! :D This is absolute amazement and I look forward to further progress with this TV set in terms of restoration work and also identifying exactly what prototype it was and when it was manufactured, keep up the good work mate!!! :D

Pete, Great photos and commentary. Almost as good as being there!

After seeing the photo of the number stamped on the rim of Nick's prototype CRT, I closely examined my two down-to-air metal bell prototype CRTs and discovered numbers on their rims I had never noticed before. One had D76, the other had D111. Both of my tubes have 14 pin stems and bases, which I believe places them somewhere earlier in the prototype tube progression. By March of 1953, RCA had provided 477 tricolor CRT samples to 177 companies.

I speculate that these rim numbers may represent a serialization of the metal bells used to assemble the tubes.

This is all just so astounding...Like watching history being made...Yeah, I know, I'm silly...

Pete, Great photos and commentary. Almost as good as being there!

After seeing the photo of the number stamped on the rim of Nick's prototype CRT, I closely examined my two down-to-air metal bell prototype CRTs and discovered numbers on their rims I had never noticed before. One had D76, the other had D111. Both of my tubes have 14 pin stems and bases, which I believe places them somewhere earlier in the prototype tube progression. By March of 1953, RCA had provided 477 tricolor CRT samples to 177 companies.

I speculate that these rim numbers may represent a serialization of the metal bells used to assemble the tubes.

I went back to my original photograph and checked for what I thought at the time were four integers. The first and fourth were lighter than the others and so I projected that they were hand stamped. Upon closer inspection, the first character could well be a 'D' with 205 following. If that is correct, and when he can find the time (Nick is young guy, not retired like us!;)), Nick might be able to confirm or deny my supposition. If so, this 20-pin prototype would fall right along the timeline.

Pete

Pete, I agree. When I get a chance, I will examine my other two metal bell prototypes. Unfortunately, they are both in sets (the Sparton and CBS prototypes), and getting to where I can read the rim numbers is a very non-trivial task. But I guess now I need to do it. One of these tube is a 6-bolt 20 pin base type, the other is a 3 bolt 20 pin base type. I would expect the rim numbers to be greater than Nick's if our theories are correct.

Phil Nelson posted on his great vintage TV site this CT-100 ad from RCA. Read the text for the amounts and brief history of RCA's prototype and CT-100 tubes made available to other manufacturers in the early '50's.This was not totally altruistic on RCA's or Sarnoff's part. They wanted color TV in the public's hands and if it took other manufacturers to get the ball rolling, so be it.

RCACT-10015GP22KinescopeAd.jpg
http://antiqueradio.org/art/RCACT-10015GP22KinescopeAd.jpg


-Steve D.

I do believe the stamping said D205, but I could be mistaken. I'll have a closer look when I get home, and photograph it with my macro lens. I'm assuming all the talk of pin counts is important because as development progressed, the 20-pin 15GP22 was the ultimate result? So earlier on they were using different basing if I understand this right, which would place my tube later on in the development timeline and peg tubes with different pin counts as earlier ones?

So earlier on they were using different basing if I understand this right, which would place my tube later on in the development timeline and peg tubes with different pin counts as earlier ones? Something like that. I liken these exercises to riding an old mountain railroad for the first time: plenty of hidden curves ahead; somebody was there before us to build the thing, but it's all new now... :yes:

Pete

Nick, The earlier tubes had a 14 pin stem and base. I would speculate that this was because they had a 14 pin stem and base in the inventory. Later on, it became obvious that additional electrical isolation was needed between the convergence pin at [edit] 7-9KV and the other pins, so a 20 pin stem and base were developed, allowing 3 blank pin locations on either side of the convergence electorde.

I just checked my Sparton metal bell CRT, and it is a 20 pin 6 bolt CRT just like yours, with a type number of C73547, just like yours. My bell rim number is D255, and I believe Pete said you rim number is D205 (?). This all seems to make sense. My Sparton set is a early 1953 NTSC set, as best I can tell.

Update: took the tube out of the box, and it's definitely D225. Only 30 made between ours, if the assumtion of a production serial code is correct. :yes:

http://videokarma.org/attachment.php?attachmentid=170834&d=1308705194

Thanks, Nick. Well it is all very interesting.

Later on, it became obvious that additional electrical isolation was needed between the convergence pin at 3-4KV and the other pins, so a 20 pin stem and base were developed, allowing 3 blank pin locations on either side of the convergence electorde.

Makes perfect sense.

Hey, speaking of convergence...

This thing has a long string of megohm resistors coming off the HV rectifier, with the convergence pot right in the middle and more resistors after it. It looks electrically just like the way it was done on the CT-100, except by that time they actually had a 50meg resistor to use in the circuit. What do your proto sets have for convergence?

Your set doesn't appear to have a convergence transformer like the CT-100, so the question becomes how did they accomplish dynamic convergence, or maybe the question is "did they use dynamic convergence". I would be curious to know if there are other connections (capacitors to be specific) to the convergence grid of the CRT?

Nick, Here is a photo of the bottom side of he CBS prototype. It appears to use large high-voltage resistors, but it has been many years since I was under the chassis, so the details are vague. I have never had the HV cage cover off the Sparton, but as it appears to be a close cousin to the production Sparton set shown in Sames, I expect it will also have 50 megohm (or similar) high voltage resistors. Both of these sets are, shall we say, more mature than your set. :-)

If this prototype dates from 1950-51, how far along was it's development?

Has anyone identified whether this is a set still running on the dot sequential principle or whether the design had progressed to the constant luminance principle with interleaved chroma?

Is there any schematic information with this set? It would be very interesting to reverse engineer this set to find out what the design comprises of.

Note: seems I missed an earlier part of this thread. I see from Ed's post that progress had moved to CPA and possibly later to the early '53 NTSC development closer to the final standard.

It will be interesting to see what the reverse engineering reveals.

Your set doesn't appear to have a convergence transformer like the CT-100, so the question becomes how did they accomplish dynamic convergence, or maybe the question is "did they use dynamic convergence". I would be curious to know if there are other connections (capacitors to be specific) to the convergence grid of the CRT?


That's exactly what I'm wondering. The other end of the resistor string has a wire that goes under the chassis, with connections to many different parts. So perhaps it does have dynamic, but it's done in a different way?


Thanks for the picture, John. I can see the 50meg resistors on that set, so you're right- it is more 'advanced' than mine. :music:

Nick, Attached is a scan of the schematic from the June 1951 RCA symposium on tricolor picture tube development. While this features a RF HV supply and differs considerably from your sets configuration, it does show both vertical and horizontal dynamic convergence transformers. It would seem quite odd if your set did not incorporate some type of dynamic convergence.

Nick, if you follow the wiper of the convergence pot, where does it go? This is where the convergence stuff would be.

Nick, if you follow the wiper of the convergence pot, where does it go? This is where the convergence stuff would be.

To the CRT, nowhere else.

I think that means that the set has no dynamic convergence, which is strange. But a full schematic will tell for sure.
If you look at the schematic that John posted you'll see a 10kv capacitor from the convergence pot to the circuitry that provides the waveforms for convergence.

There is a doorknob cap mounted under the chassis, but I have no idea what it's connected to.

For John's request and for comparison, my 6-bolt, 14 pin prototype tube is paper tagged;

Developmental type - C73293C
Serial - L3046R

Rim stamped - D229

And it has acquired a swooping crack right across the faceplate but not edge to edge. No idea how that happened. Have not looked at it in 5 years. Gotta be careful now.

Dave, thanks for the data, and that is a real shame about the crack in your faceplate.

The museum's 6 bolt, 14 pin tube is paper tagged:

Developmental type - C73293C
Serial: L1188
Also on the tag: 1350

I can't find a number stamped on the rim, but my rim is rusted and dented.

We also have a single gun developmental tube, paper tagged:

Developmental type: C73275
Serial: CR3089-1, DK29217
Also on the tag: H-357

Rim: DT45

In paint on the metal shell: DK29217

I thought these numbers on the rim of the CRTs were making sense as a serialization number for the shells and therefore the CRTs. All the rim numbers seemed to match up with the likely chronological sequence of the tubes. But Dave's CRT rim number seems out of place. So maybe the rim numbers don't mean much...could be just lot or batch numbers for the bells.

Also, I checked the rim of the 3 bolt 20 pin metal bell prototype in my CBS proto set, and it has no rim number. And the part of the paper tag with the "C" number is missing. But I a certain it the the youngest of the metal bell prototype tube identified so far, due to the 3 bolt faceplate mounting and the fact that the mu-metal shield is an external component. I believe the C73293 and C73547 series tubes had an internal mu-metal shield incorporated into the design.


If anyone else knows of any other metal bell prototype CRTs, please get me in touch with the owner. Thanks!

John, given the riches I have with my little collection of rare sets, the spare parts I have and all the help I get around here, a small crack is nothing. My minor contributions are more important than a crack. Knowledge is everything.

John, your supposition that the 3 bolt version is the earliest one conflicts with the information that Dave gave me some time ago. Here is what he wrote:

This tube [the 6 bolt version] was use in the tri-color models 1 and 2 and possibly the 2A. Model 1 was the first RCA demo to the FCC. These tubes were circa April, 1950 to February, 1952. Models 3 and 3A used a 3-bolt version. Starting with the 3, they improved the trajectory of the guide bolts for the shadow mask alignment. The model 4 appears to be the first of the glass tubes. Most of what I know can be found in the RCA Color TV submission to the FCC...the "red book"...and in the second "Proceedings of the IRE" on color television.

I'm under the microscope now. I can stand to be corrected from the dimunition of time. The 6 to 3 does seem to be logical as they improved as does the 14 to 21 pin base.

Perhaps we should start another thread just for these efforts. I would like to know how the mechanics of these seemingly eccentric bolts worked. These are not just locking bolts but perform a function...but what?

I am not surprised that RCA had to develop a shadow mask that was moveable for the developmental stage until mfg could catch up with precision.

It would take an artist to move these bolts to allignment under the light box used to align the shadow mask as seen in the documentation. You would think that any one bolt could distort the shadow mask not to mention 5 more.

John, you are almost always right.

Uh oops. Poor choice of wording on my part. What I intended to say was the 3 bolt mounting version of the CRT post dates the earlier 6 bolt versions.

But I a certain it the the youngest of the metal bell prototype tube identified so far, due to the 3 bolt faceplate mounting and the fact that the mu-metal shield is an external component. I believe the C73293 and C73547 series tubes had an internal mu-metal shield incorporated into the design.



Another wrinkle, then: mine has an external shield, which sits on the plastic (capacitive?) insulator.

http://videokarma.org/attachment.php?attachmentid=170845&d=1308840754

In other developments, I believe I have narrowed down the demodulator tubes. They are positioned in a hard to reach area, under the support for the yoke. I wiped away the dirt to find R-Y and B-Y pots.

http://videokarma.org/attachment.php?attachmentid=170846&d=1308840958



Also, thanks to John's schematic of his prototype set, I did some looking around on my chassis and believe I have found how dynamic convergence is done. I was apparently incorrect when I told Steve that the only wire connected to the convergence pot wiper is the CRT: looking again, there is a wire leading down to a chassis isolated doorknob cap which then leads into small transformers in the vert and horiz sections. I believe these would be the dynamic transformers, based on the wiring I'm seeing. The numbers on the horizontal transformer are T-6942 and vertical is 208T9 and 274113.

http://videokarma.org/attachment.php?attachmentid=170847&d=1308841327
http://videokarma.org/attachment.php?attachmentid=170848&d=1308841327

The numbers on the horizontal transformer are T-6942 and vertical is 208T9 and 274113.




I believe that last number is a Mfg and Date code, RCA built (274) and 113 would be the 13th week of 1951.
The transformer in your last picture has a 274125 number or mid 1951.

Are these off the shelf RCA parts or were they made specifically for the Prototype?

The transformer in your last picture has a 274125 number or mid 1951.

That one is actually a power choke, and it does have an RCA stamp on it.

Nick, I am comforted by your discovery of convergence transformers. :-) BTW, that schematic is from a RCA CRT symposium, not a set I have.

I may be wrong (I often ma) about the mu-metal shield. The C73293 CRTs are shown to have an internal mu-metal shield. I don't have and explicit data on the C73547 CRTs, but the one in my Sparton also has a external mu-metal shield, so this would seem to indicate the C73547 series tubes use an external shield. Attached is an assembly drawing of the C73293 series tube.

I have been reading some interesting IEEE articles on early CPA. An especially interesting one is by Bernard Loughlin who worked for Hazeltine Labs in the early 50's. He presented a paper at the Seventh Chicago Spring conference on Broadcast and Television receivers in Chicago in 1966 on the PAL TV system. He makes reference to the early CPA and he puts CPA in the context of what later transpired with the evolution of world standards.

CPA or color phase alternation appears to have originated to help offset the problem of limited bandwidth of the RMA US TV channel eg 6MHz. It is interesting to think that 6MHz is still with us for the ATSC system. But it seems that by the early 50's, after the constant luminance with restricted bandwidth chroma channels has been accepted that somehow interleaving the chroma with he luma as cleanly as possible was the ultimate challenge.

The original NTSC CPA approach was to vestigially modulate B-Y and R-Y with a subcarrier of 3.89 MHz and phase alternate B-Y at either field rate or line rate. (Europe ultimately chose alternating R-Y at line rate). The vestigial sideband approach was to extend the chroma bandwidth and the B-Y alternation would minimize quadrature crosstalk between R-Y and B-Y.

It appears of the two options, the 1952 field test used field alternation rather than line alternation. Is this correct? Slight phase errors would introduce flicker on image edges or chroma transitions due to the crosstalk not being properly integrated or cancelled. It appears that in 1952, a one line delay line was impractically expensive for consumer use and so the true benefit of CPA Phase Alternate Line had to wait a decade and a half.

It appears that the failure of the 1952 CPA test was due to color subcarrier to sound carrier beats (600kHz) and vestigial sideband quadrature crosstalk. Lowering the subcarrier to 3.58MHz and the IQ working overcame the most of the problems.

With regards to the prototype, it appears that if it is indeed still configured for 1952 field CPA, the conversion to IQ NTSC should be relatively straight forward. The crystal frequency of 3.89MHz should indicate whether it is remains the CPA prototype. Chroma demodulation would be restricted to equal band R-Y/ B-Y demodulation since there is no bandwidth differentiation between I and Q in the original CPA prototype. That is, unless it was later further modified.

Glad to hear you found the convergence circuitry. Now it makes sense. The next mystery is to figure out what color scheme it uses.

This prototype I find incredibly interesting in light of the early development of the NTSC standard. Certainly, it should be possible to generate a 1952 CPA signal to run the set. I would certainly hope that the set not be modified from the CPA design if it indeed is still a CPA receiver.

Is the subcarrier crystal 3.89MHz?

I came across another interesting paper published in the March '53 Proceedings of the IRE. It is entitled "Generation of NTSC Color Signals" by Joseph Fisher and pertains to the earlier CPA specification.

It appears that for the NTSC '52 tests, field rate R-Y switching was employed. Vestigial sideband equal bandwidth R-Y and B-Y chroma channels were used. Color subcarrier was 3.89MHz and it appears only standard 1/2 line offset interleaving was used.

CPA at field rate as opposed to line rate probably was a better choice in 1952. The reason for CPA was to cancel phase errors in transmission and to facilitate vestigial sideband chroma channels without quadrature crosstalk. Because there was no way to electronically delay and combine alternate field or line information economically in 1952, the errors would be cancelled visually. This is very much akin to simple PAL in Europe. The field rate equivalent to "Hannover Bars" would result from transmission phase errors.

The real failure of the 1952 CPA tests therefore must have been due to the flickering akin to Hannover Bars and the 610 kHz chroma subcarrier to audio carrier beat (this was before the line and field rate was shifted to 15,734.26Hz and 59.94Hz respectively to ensure that the sound carrier was a multiple of the scan rates). In addition, the alternating R-Y axis would prevent proper 1/2 interleaving of the chroma within the luma.

Note that PAL later adopted the 1/4 line offset to help mitigate the interleaving problem. PAL also introduced a picture rate subcarrier frequency offset (25Hz) to further conceal the interference. (In hindsight, a 29.97Hz offset could have been added to help conceal the NTSC dot crawl. But the standard was already established and the simpler luma to modulated chroma arrangement in NTSC probably makes this unnecessary).

I
It appears of the two options, the 1952 field test used field alternation rather than line alternation. Is this correct? Slight phase errors would introduce flicker on image edges or chroma transitions due to the crosstalk not being properly integrated or cancelled.

Yes, field alternation was used. Wentworth's book on color television engineering states that flicker was bad due to difficulty of maintaining the exact relationship between the alternate phases in transmitter and receiver. The air-core coil that Nick found looks suspiciously like it was built to reduce variations with temperature, spacing to the shield can, etc., etc., but we won't know until we discover whether there is a phase switching circuit.

Also, the crystal appears to be missing, so we don't have that confirmation.

An aside regarding frequency interleaving: during the analog to digital transition period in the US, digital channels that were lower adjacent to analog channels were required to have a precise frequency offset to reduce the possibility of visible beats between the digital pilot carrier and the chroma of the upper adjacent analog signal - a re-application of the principle developed by NTSC long ago.

That's exactly what I'm wondering. The other end of the resistor string has a wire that goes under the chassis, with connections to many different parts. So perhaps it does have dynamic, but it's done in a different way?:

The transformer is only needed for the vertical component. The horizontal component can be AC coupled. We looked at the same thing for dynamic focus back in the late 1980's. The horizontal component was easy to add the vertical component more difficult. Is that really a high voltage vertical transformer?

Nick, I am comforted by your discovery of convergence transformers. :-) BTW, that schematic is from a RCA CRT symposium, not a set I have.

D'oh! Sorry about that, I've been pretty hasty about reading these last couple days. There was some bad weather that came through recently, and it knocked out my internet connection. Because of that, I've had to use spare time at work to post. Now that I have my internet back though, I'm free to post at will. Muhahahaha! :banana:

This prototype I find incredibly interesting in light of the early development of the NTSC standard. Certainly, it should be possible to generate a 1952 CPA signal to run the set. I would certainly hope that the set not be modified from the CPA design if it indeed is still a CPA receiver.

Is the subcarrier crystal 3.89MHz?


*sigh*

If only there had been a crystal installed in the chassis, it would have made the mystery of what standard this chassis uses a lot easier to figure out that's for sure! Since it didn't have one though, the best I can do is trace the circuit and try to determin if it's still CPA or if it was converted to use the later 3.58MHz subcarrier. I'm still leaning towards CPA though, considering the 'CPA transformer' is the one that's still connected.

CPA at field rate as opposed to line rate probably was a better choice in 1952. The reason for CPA was to cancel phase errors in transmission and to facilitate vestigial sideband chroma channels without quadrature crosstalk. Because there was no way to electronically delay and combine alternate field or line information economically in 1952, the errors would be cancelled visually. This is very much akin to simple PAL in Europe. The field rate equivalent to "Hannover Bars" would result from transmission phase errors.


One of the things I'm itching to figure out with this thing is if the edge effects and bars with CPA really are as bad as people make them out to be, it's one of the motivating factors to get it working as it last did. I'm hoping my brother will stop by this weekend, so we can do some digging in the color section and determine for sure what it's supposed to do. He should be able to sketch the circuit in only a couple hours, and usually takes payment in beers. :thmbsp:

The transformer is only needed for the vertical component. The horizontal component can be AC coupled. We looked at the same thing for dynamic focus back in the late 1980's. The horizontal component was easy to add the vertical component more difficult. Is that really a high voltage vertical transformer?

I don't think so, it looks much too small. Everything is on the other side of a dooknob cap, so I'm assuming right now that everything having to do with convergence is also low voltage.

I came across another article entitled "General Color-Receiver Design Considerations" presented at the fall meeting of the IRE and RTMA in October 1952 by staff at Hazeltine Labs. It is a description and details on CPA receiver design.

On the final page of the article is a complete diagram of a CPA demodulator. The color oscillator has no crystal! A 12AT7 is used: one half the reactance control and the other half a Colpitts oscillator. Only LC components and no crystal.

I will try and post the drawing and article tomorrow. But the decoder line up in the drawing includes the following:

12AT7 Reactance/3.89MHz Oscillator
1/2 6AL5 Clipper
6CB6 Bandpass amp
6AS6 B-Y demodulator
6AS6 R-Y demodulator
1/2 12BH7 B-Y matrix amplifier
1/2 12BH7 R-Y matrix amplifier
1/2 12AT7 G-Y matrix amplifier
6CB6 Isolation Amplifier (or Color oscillator buffer output)
1/2 12AT7 Field Recognizer Driver
1/2 12AT7 Field Recognizer Phase Detector
12AT7 CPA Multivibrator
1/2 12AT7 Field Recognizer Keyer

I will try and post the drawing and article tomorrow. But the decoder line up in the drawing includes the following:

12AT7 Reactance/3.89MHz Oscillator
1/2 6AL5 Clipper
6CB6 Bandpass amp
6AS6 B-Y demodulator
6AS6 R-Y demodulator
1/2 12BH7 B-Y matrix amplifier
1/2 12BH7 R-Y matrix amplifier
1/2 12AT7 G-Y matrix amplifier
6CB6 Isolation Amplifier (or Color oscillator buffer output)
1/2 12AT7 Field Recognizer Driver
1/2 12AT7 Field Recognizer Phase Detector
12AT7 CPA Multivibrator
1/2 12AT7 Field Recognizer Keyer


Oh, baby! This might be a huge help in locating what circuits do what in this set, I can't wait to see what it looks like!

*sigh*

If only there had been a crystal installed in the chassis, it would have made the mystery of what standard this chassis uses a lot easier to figure out that's for sure!
Since the crystal is missing, I wonder if it would be feasible to connect either a sweep generator plus scope, or a spectrum analyzer with tracking generator, to various circuits in the chassis to figure out their resonant frequencies and bandwidths as currently tuned. Or, get a 3.89 MHz crystal along with a 3.57 MHz one, isolate and apply power to the oscillator circuit with each crystal, and see whether either or both work in the circuit and measure relative RF outputs to determine which frequency the circuit might have used when it last operated.

Here's another idea: Try using a dip meter near the various circuits, if it is possible.

I wonder if it would be feasible to connect either a sweep generator plus scope, or a spectrum analyzer with tracking generator, to various circuits in the chassis to figure out their resonant frequencies and bandwidths as currently tuned.

Sweeping the bandpass amplifier is a great idea! The response may not be peaked at the subcarrier. The peak could be staggered to make up for any roll off in the IF or bandpass/lowpass filtering.

But the information still could be usefull if you looked at the overall video response of the chassis.

Please find attached two papers, both from Hazeltine. The first one on general color receiver design pertains to CPA only. The last page has a nearly full CPA demodulator. Note the demodulator does not use a crystal! The design is a straight reactance controlled Colpitts oscillator. This is interesting in as much as it is expected to keep sync over the entire line from onlyeight cycles of gated burst reference! Note the color hold control- if there is no crystal on this prototype I would trust there is a color hold control on the front!

The second Hazeltine paper is by Bernard Loughlin. His name conjures up a lot of early NTSC development. His 1966 paper is timed with the launch of PAL in Europe. It is interesting to read his reflections since the NTSC did much of the earliest PAL and PAF work.

I find his interesting note in passing on the second page (numbered 154) under the heading Stationary Axis. Mr Loughlin refers to his October 1951 IRE paper whereby the R-Y axis was stationary and the B-Y axis switched or inverted 180 degrees. He goes on to state the 1952 PAF NTSC testing made the B-Y axis stationary and the R-Y axis switched. In PAL, the R-Y switches at line rate.

I would be interested to see how closely the prototype receiver follows the Hazeltine decoder.

It's a minor thing, but it made me recall the crystal socket that was discovered last Saturday. Went back to my photos and confirmed that the subcarrier oscillator was, in fact, built on a removable chassis. The tube is a 6U8, one RCA used in this circuit in pre CTC2 chassis before introducing the 6AN8. Unfortunately, the name of the builder of this chassis is no closer to being known. The crystal in this photo was from a CTC2.

Pete

if there is no crystal on this prototype I would trust there is a color hold control on the front!

Perhaps I should have been more clear:

There was no crystal INSTALLED, though there is a SOCKET for one.

Was thinking you will need to get some sort of power supply to power up sections of the chassis. I think the power supply from one of the many 1948-1950 B&W RCA projection sets would be a good fit. Has three 5U4G, it is an RCA chassis, just about the right period. And there has to be a couple of guys with spare chassis for these.

I have many doner chassis at my disposal, I would never deprive another collector of the opportunity to restore something like a projection set in the process of getting this thing to work. I'd much rather use a common chassis, like a Maggie 6V6 amp or something that no one will miss.

Went back to my photos and confirmed that the subcarrier oscillator was, in fact, built on a removable chassis. Pete

Is there a chance that some markings are hidden and would be visible if the subchassis is removed?

You haven't been around long enough;-). There are way too many
of those projection sets around and I bet there are few collectors
that have just the chassis to use for flybacks and hard to find parts.
It is very unlikely that any have used the power supply chassis. I think
would be a very good fit.

I guess if one fell into my lap I'd use it, but it would have to be pretty much free. I can't justify much more expense with this chassis, the last thing that will be bought for it is a nice cabinet to house it when it's finished.

Is there a chance that some markings are hidden and would be visible if the subchassis is removed? While I didn't take under-chassis photos, from what I recall, your idea could probably be tested without completely removing that assembly; there seem to be only four screws in the photo associated with the chassis.

I thought perhaps the separate chassis was for flexibility during engineering design and testing.

I'd of course love to work on the chassis, but there are no current plans to do so at this time.

Pete

I doubt there are any markings under the panel, for all intents and purposes it's just another subchassis.

Found a patent online which may be of some use to us:
http://www.freepatentsonline.com/2736859.pdf

It is a patent filed by Dalton H. Pritchard and Alfred C. Schroeder (assignors at RCA) on July 25, 1952, which details a 'Color Phase Alternation Control System'. It outlines a system whereby the phase of the red syncronous detector is flipped by 180 degrees at field rate by a transformer with windings arranged to accomodate this change in phase. According to the patent, this would eliminate any reflective errors induced in a system incorporating a double ended delay line, while at the same time reducing cost.

"Previously, color phase alternation has been brought about in the following manner. Each of the synchronous detectors in a receiver were coupled to a different tap point on a delay line having a total delay of 360 degrees of the color carrier frquency. During one field a wave of color carrier frequency was applied to one end of the delay line so that different phases of the wave were available at the different tap points. During the next field the wave of color carrier frequency was applied to the opposite end of the delay line. As is well known, the closer the tap point to the energized end of the delay line, the nearer it is to the phase of the wave applied to that end. Therefore by energizing opposite ends of the line during successive fields the phases of the wave at the different tap points are interchanged. Some difficulties have been experinced in that reflections from the non-energized ends of the line interfere with the apparent phase of the wave at the various tap points. In addition, the delay line attenuates the wave applied to it so that as the wave progresses from one of the line to the other its amplitude is reduced. Because the line is energized from one end during one field and from the other end during a succeeding field, the amplitude of the wave at any tap other than the one located at the exact center of the line changes from field to field. At the center the attenuation of the wave is the same irrespective of the end energized. Such an arrangement is useful where 2 or more synchronous detectors are employed.

In accordance with one of the objects of this invention, the necessity for using a delay line is completely eliminated and the attendant difficulties are entirely avoided in arrangements requiring only 2 different phases of the wave of color carrier frequency during any one field."


Sheet 2 of the patent outlines the actual phase alternating circuit; if Wayne's supposition that the 'CPA' transformer in this chassis has something to do with phase switching:

The air-core coil that Nick found looks suspiciously like it was built to reduce variations with temperature, spacing to the shield can, etc., etc., but we won't know until we discover whether there is a phase switching circuit.

Then I would assume that the 'CPA' transformer in this chassis is wired in much the same way as the patent outlines, we'll know for sure later on tonight when Tim and I trace the circuit out and compare it to the ones found here and in some of the other literature forwarded to me over the past few weeks. Additionally, the text of this patent may also explain why there is also a blank hole in the chassis marked 'delay'. It's possible that the 'delay' on this chassis has more to do with the type of delay described by the patent, and not any sort of later delay (such as the common luma delay lines) that might have been associated with later NTSC standards.

I attached a Hazeltine article on Friday but upon looking for it this evening it is gone!? Don't know what happened but I will see if I can repost it tomorrow.

In the Hazeltine diagram, R-Y phase inversion is accomplished by simply using a field rate multivibrator (12AT7) locked to a field recognizer detector (another 12AT7) to the correct field. The CPA transformer secondary is center tapped so that either end (180 degrees apart) is selected field by field to supply R-Y or -(R-Y) as required.

Note that the Hazeltine implementation at that time did not include a crystal controlled subcarrier oscillator.

Did anyone of you have a chance to see the article/diagram I posted on Friday while it was there?

is this the one? I downloaded a copy... :-)

If you're referring to post 177, it's still there.

It was a paper by Hazeltine, I assumed it was removed on purpose, not by the author... If there are no objections I will repost it.

I attached a Hazeltine article on Friday but upon looking for it this evening it is gone!? Don't know what happened but I will see if I can repost it tomorrow. (snip)
Did anyone of you have a chance to see the article/diagram I posted on Friday while it was there?


You posted at 12:35 and I copied it at 1:55, but when I went to view it on my better monitor at home at 5:30PM it was gone. I assumed that you had canceled it to correct the upside down drawings.

One question.
The underside of this chassis does not show chassis mounting screws or mounting holes.

Is this common on prototypes?

Jas.

.

You posted at 12:35 and I copied it at 1:55, but when I went to view it on my better monitor at home at 5:30PM it was gone. I assumed that you had canceled it to correct the upside down drawings.

If I've done this reply correctly, it is attached.

Jas.

That's the one, thanks. Yes, I did correct the upsidedown drawing and posted it. But later it was gone. Very odd.

I suspect their were many variations to the CPA demodulator. Note from the time this article was written, it appeared that CPA support was dying. I believe it was just too difficult to implement effectively in 1952.

Note the upside of IQ and a lower subcarrier frequency was elimination of the crosstalk and the bothersome flicker. The downside was reduced Q resolution and the lower subcarrier frequency reduced the luma bandwidth hence luma resolution.

Engineering is all about trade offs.

A sidenote: the BBC was planning to adopt a modified NTSC as late as 1966. The UK 625 line channel is 8MHz wide with the sound carrier 6.0MHz away from the video carrier. This means that the bandwidth was available for full double sideband chroma (4.43MHz +/- 1.4MHz). Hence IQ working in the UK would not have been necessary. The UK could have had wide matching bandwidth for B-Y and R-Y. The dropping of NTSC in favor of PAL in the UK was very late. Proof of this were the rubidium frequency standards used at Television Centre and Lime Grove in London: the standards were cut for NTSC and augmented equipment was required to provide the PAL subcarrier frequency (1/4 line offset plus 25Hz).

I think NTSC for the wide channel UK 625 would have looked terrific and better than PAL.

Some may refer to NTSC as "Never Twice the Same Color"

But in a similar vein, PAL may be referred to as "Problems are Lurking"

Spent this whole weekend doing a combination of things- a little woodworking to get closer to finishing a decorative shadow box for the ground breaking shovel at work, and Tim did some circuit tracing on the chassis. He started at the tuner and worked through the IF strip, at the end of the day he got as far as the first video amp tube (6AG7). Next weekend we will be getting close to the demod and CPA sections, so I'm hoping by then that we will finally be able to get a feel for how this set operates. Circuit tracing is labor intensive though, many breaks are required to avoid getting burned out and to avoid making mistakes. Right now, everything is on paper. When he is finished, it will be drawn out with MS Paint or a schematic program so it's easier to read. One thing is clear: it will be a very large schematic indeed. We both had the idea of breaking this up into sections: tuner/IF, luma channel, chroma, matrix, and finally deflection. That should make it easier to understand.

I think NTSC for the wide channel UK 625 would have looked terrific.
I have heard of a signal called "NTSC 4.43", and I think it is basically NTSC color encoding but using the frequencies common to most PAL signals (625 lines, 50 fields/25 frames, and a 4.43 MHz color subcarrier. One or more models of Sony monitors I have worked with had this as one of the signals they could accept. An online search should turn up more about it, or maybe others here already have details to share.

There are also several variations of PAL color signals (B, G, M, and several more), and one of them is 525 lines, 60 fields, and a 3.58 MHz color subcarrier if I remember right.

Interesting reads, IS THIS an electronic version of the later and cheaper color wheels or similar with color phase shift?

Nope. Color wheels work with sequential fields of color which is a different principle entirely.

I have attached another version. The drawing is sideways: at least it is better than upsidedown.

It is interesting to put this paper on CPA in context with the development of the all-electronic compatible color. By mid 1952, much of the development of what would finally end up in the December 1953 standard was there. The constant luminance principle was there as was the chrominance quadrature modulated on a odd multiple of half line frequency to facilitate luma/chroma interleaving. But also the elements which would soon disappear including the burst pedestal as was assymetrical B-Y and R-Y bandwidths and the higher subcarrier frequency.

It is interesting that the original RCA RGB Dot Sequential sample frequency is fairly close to the later NTSC subcarrier of 3.58MHz. The original impetous for CPA was to extend the bandwidth of the chroma channel within the limited bandwidth of the US 6MHz wide channel. Hence the choice of 3.9MHz for the CPA subcarrier I suggest was for two reasons: to provide wider bandwith (vestigial sideband chroma) for both R-Y and B-Y and to extend the luma channel response. Remember that there is a luma 3.58MHz trap in early NTSC receivers which effectively cuts the high frequency luma response to 3MHz or less. A 3.9MHz chroma subcarrier would have extended the luma response a little bit.

CPA employed for PAF or PAL (Phase Alternate Field or Phase Alternate Line)was simply inverting the R-Y axis at either field rate or line rate. The reason for doing so was to eliminate differential phase errors which would result in hue errors and to cancel quadrature crosstalk between R-Y and B-Y at demodulation. Remember, crosstalk was eliminated with I and Q by ensuring both were double sideband to 500kHz and only I extended from 500kHz to 1.5MHz. CPA facilitated vestigial sideband R-Y and B-Y and the crosstalk was to be cancelled by averaging.

In 1952 only visual averaging of the PAF and PAL was available which led to the crosstalk and hue errors resulting in the annoying field flickering (PAF) and a vertical line crawl (PAL). The European engineers later termed the PAL line crawl as "Hannover Bars" and may be readily seen on what is referred to as "Simple PAL" decoders or PAL decoders without the electronic delay line averaging.

In 1952, the NTSC was exploring PAF as the field flickering was deemed less objectionable to the line crawl. I agree with the later NTSC assessment that moving away from the CPA to the I Q solution was one step beyond CPA in the development of compatible color TV. Successful deployment of CPA with PAL fifteen years later depended upon the one-line delay line which was not readily available in 1952.

We should look forward to finding out what remains of the CPA circuitry in this extremely unique prototype. I trust you will share with us the circuit as you trace it. I am particularly interested in the CPA transformer: the alternating R-Y phase I feel would have been derived from reversing at field rate either the chroma before demodulation or the regenerated subcarrier used for R-Y demodulation. I suspect the transformer is in the chroma signal path as per the diagram in the attached article?

I suspect the transformer is in the chroma signal path as per the diagram in the attached article?


Actually it's closest to the subcarrier oscillator, so right now my assumption is if flips the reference signal 180 degrees on alternating fields for R-Y. Only time will tell for sure, this coming weekend we are hoping to delve into the demod sections in order to figure it out. Tim did spot an odd part that I hadn't previously seen: right near the CPA tranformer hidden under some variable capacitors there is a toroid with 2 or 3 windings on it. It's about an inch and a half in diameter, and looks to have something like #30 wire wrapped around it. We have absolutely no idea what its purpose could be.

Good gawd ya'll, it's beaen days now, the suspense is killn' me! Updates, puleaze!

Patience, grasshopper. There is some discussion going on behind the scenes with the early color guys, I don't want to release any information until I am sure of what I'm looking at (to avoid confusion). Right now, I have most of the chassis schematic sketched out on paper. Once the rest of it is done it will be transferred to computer graphics so it's easy to read, and I'll post it up here for all to see. I still need a couple weeks to get it all finished up, only deflection and a few random pots remain...

I shall remain quietly in wait;) regards, tommy

A little confusion is a fundamental quality in a good Forum.

It's just that the only thing that to me that could be as interesting or as suspensfull (Did I spell that rite?) as this adventure would be some un-earthed Zenith color proto's or documentation showing the evolution of Robert Adler's beam deflection color demodulation circuitry! :)

It's just that the only thing that to me that could be as interesting or as suspenseful as this adventure would be some un-earthed Zenith color proto's or documentation showing the evolution of Robert Adler's beam deflection color demodulation circuitry! :)

Zenith was unique in that they first made FCC testing sets for both the CBS system and then later for the NTSC system. If this is not an RCA prototype, then it most probably is a Zenith. (While Westinghouse was in it early, I don't think they were in it this early.)

James

My brother Tim stopped by on Saturday, and I gave him the paper copy schematics. Being that there are folks on here who have an interest in viewing what we have written down to date, I asked if he could 'computerize' everything we have so I can upload it. A number of people I emailed the paper scans to made comments to the effect that it's just too hard to interpret, and I have to agree. For example, just the IF section takes up close to 3 sheets of regular printer paper.

As soon as he has everything in order, I will post the result here. We are hoping to have it done by the coming weekend.

It is nice to hear of your progress with the documenting of your color prototype TV chassis. I look forward to learning more.

ditto!!!!!

Ditto, me, too, even if I don't understand a lot of the "Tech" stuff...I sorta get the general "Gist" of it-I think, anyway, but that's about it...

Might have a potenial power supply, it's from an old organ. Thanks to Bob G for the parts. Top transformer is the B+ stuff, bottom is filament only. :yikes: Should have enough power to do the job, I think. :D

http://videokarma.org/attachment.php?attachmentid=171134&d=1311474876

Yeah, building a power supply like that will really show you how much power those filaments need. I think I had to use a 15A filament transformer to run my GE 802's power supply, where the filaments consumed something like 12A. What's the filament draw on your set going to be?

What's the filament draw on your set going to be?

No idea, but this filament PTX came from an organ which always have a bazillion 12AU7's in them. I don't think it will be a problem as far as that goes, I just hope I can come up with all the B+ supplies it's gonna need. I think right now I'm looking at a 250-ish rail, 380-ish rail, some yet unknown B- supply (maybe around ~100), and possibly a small positive bias supply. Interestingly, one of the filament windings on the B+ PTX is 6.6v center tapped... I guess I could always run 5U4's at a volt more than normal, but perhaps 3DG4's would be more appropriate? :scratch2: Then again, it's entirely possible that the voltages will get a little lower once the thing is loaded down really good.

Might have a potenial power supply, it's from an old organ. Thanks to Bob G for the parts. Top transformer is the B+ stuff, bottom is filament only. :yikes: Should have enough power to do the job, I think. :D

http://videokarma.org/attachment.php?attachmentid=171134&d=1311474876

So, I guess what we've got here, is an organ donor? :scratch2:

Sorry... late night humor :)

Interestingly, one of the filament windings on the B+ PTX is 6.6v center tapped... I guess I could always run 5U4's at a volt more than normal, but perhaps 3DG4's would be more appropriate?.

Since the early vacuum tube TV days, the ubiquitous 5U4 has gone from the lowest-priced commonly-replaced bottle to being quite dear today. I'd say running those babies at 6.3 volts could get expensive in a hurry. I wonder if they make 1.3 volt 3 amp pilot lights?

On a twin-tube "B" supply, if one tube opens a filament, the other tube promptly melts before the user notices and can shut the system off. On 5U4's this problem seemed to be worse with the fat G's and first generation GT's than with the GB's

If the filaments were wired in series, this would protect the second tube.

Are the tubes in the picture from the organ? If not, any idea what tubes the organ used?

<---> On a twin-tube "B" supply, if one tube opens a filament, the other tube promptly melts before the user notices and can shut the system off. <--->

Someone in this forum pointed out several years ago that wiring a 5U4's plates in parallel and connecting to *just* one side of the B+ winding, then doing the same thing with a second 5U4, but with both tube's filaments connected in parallel to the 5 volt PTX winding, will possibly save the other tube and the PTX in the event of a failure.

The idea is that if one tube shorts and blows the filament open, the remaining tube will be the only load on the transformer. The B+ will drop, but the transformer will not be overloaded.

A 6.6 volt filament winding is sometimes used if the power supply is on one chassis and the load circuitry is on another separated by 2 to 4 feet of heavy cable. The voltage drop through that cable can be in the range of ~0.3 volt if the filament draw is substantial.

Cliff

...
A 6.6 volt filament winding is sometimes used if the power supply is on one chassis and the load circuitry is on another separated by 2 to 4 feet of heavy cable. The voltage drop through that cable can be in the range of ~0.3 volt if the filament draw is substantial.

Cliff

And you can use larger wire for the filaments.

Because the damper tubes in those days may suffer cathode to filament breakdown, was there originally in the prototype previously provision for a separate filament winding for the damper?

Terry

No, only an isolation transformer off the heater string that supplies all the other tubes.

Please let me know what else you may need for the power supply. If I have anything you need, it's yours for the shipping cost.
I have, literally, a ton of PS iron, etc..

Rick

OK, thanks for the offer! Right now I have the chassis Bob gave me, with a pair of tranformers that look like they are up to the task, twin ST glass 5U4G rectifiers and enough stuffable caps to build something useful. If I need anything more, I'll keep you in mind.

Update: I may have a line on a very nice cabinet for this chassis. It's a 9-T-79, which uses the 19" tube. It's got 4 doors, 2 for the screen and 2 for the speaker. Very classy. The seller says it's 24" deep, which should be more than enough to hold the entire color chassis without any of it sticking out. Only question is, will I be able to make a nice bezel to adapt this cab to the smaller 16" pix tube mask?

I've already got an idea on how to make a mask for it, we could whip one out in less than a day. ( If nothing goes wrong :3 )

Here's the set in question:

http://nashville.craigslist.org/fuo/2520420291.html

http://videokarma.org/attachment.php?attachmentid=171505&d=1315187259

http://videokarma.org/attachment.php?attachmentid=171506&d=1315187259

I already sent a payment through Paypal, but she has never used it before so we'll see if it goes through OK. If so, I have a job up on U-Ship right now to get it here. There is also another potential Bob alerted me to, this time on Ebay:

http://www.ebay.com/itm/RCA-Victor-TC-168-Antique-TV-Parts-Repair-NE-Ohio-1950s-/300594709988?pt=LH_DefaultDomain_0&hash=item45fcd745e4

http://videokarma.org/attachment.php?attachmentid=171507&d=1315187259

Of the 2, the second one would be better since it has the smaller 16" pix tube. The developmental tube would fit right in, no mods at all. I have to admit though, I really like the looks of the 19" one with it's double doors and all. I suspect I will end up with both, and I'll have to choose. I have promised a friend first crack at whatever I don't need (tubes/chassis), anything else will be offered here at a very low price. :thmbsp:

Looks like two 16" sets to me...?

I thought so too, but she looked at the back of the first set at my request: it's a 9-T-79, which uses the 19AP4.

You know what they say about looking twice! At first glance both tubes looked the same wrt to the speaker, but I can see the difference now.

Either way, I think I now finally have a chance at getting this thing into a very nice looking cabinet. Now if I could get those stinking schematics finished...

So, I guess what we've got here, is an organ donor? :scratch2:

Sorry... late night humor :)

Nick! I was looking at the schematic for the first Westinghouse. It shows two B+ supplies, using three 5U4's. Two of The 5U4's are connected in parallel and supply the 280 volt source. The remaining one supplies the 390 volt source. The original transformer had a tapped HV secondary plus two five volt rectifier windings. I would also go with a different power supply chassis, like from a Magnavox radio.

I can always redo the one I have, if I find that one supply requires more current. I have 4 Coke bottle 5U4G's and plenty of caps, so I don't think it will be a problem.

Unless I overlooked something...Harry Poster thinks the previous owner just plugged in tubes to sell the set. It would be interesting to see date codes, tube mfrs, and as the schematic progresses if the tubes might be correct for the circuit.

Harry Poster thinks the previous owner just plugged in tubes to sell the set.


I don't think that's accurate. All the data thus far points to the tubes being of the right type and in the correct spot for their intended purpose, the only one with a date code later than about 1954 was the 1B3GT HV rectifier. All the others look to be period correct, though a few aren't even connected underneath.

It would be interesting to see date codes, tube mfrs...


I'm still in the process of figuring out a way to get all that data into one picture, I don't think it's gonna work. Too much info, it would clutter up the photo. Instead I labeled all the tubes with their type, and perhaps I will create a spreadsheet with all the other info linked by tube number (V23, V24, ect). The chassis has labels printed on it, so it should be easy to figure out.

Just won the TC-168 set on Ebay and I'm still working on getting the other one here from Nashville, should be a week or so before I am looking at them both. Just waiting on U-Ship guys to bid low enough.

Just won the TC-168 set on Ebay and I'm still working on getting the other one here from Nashville, should be a week or so before I am looking at them both. Just waiting on U-Ship guys to bid low enough.

GREAT Nick! I think this one will be a good match for the prototype. Keep me posted RE: the 19"

GREAT Nick! I think this one will be a good match for the prototype. Keep me posted RE: the 19"


I think that in terms of being the easiest to adapt to the proto chassis, you are correct. However, I'd just LOVE to have the double door one. Something about it just says 'you know you want to', know what I mean?

TC-168 showed up tonight, not in very bad shape at all. Finish needs touching up, but all in all I'm happy for only $100 spent. Proto chassis fits like a glove, not even an inch on either side of it and the support legs for the CRT mask wouldn't make it at all. Gonna have to figure something out for the CRT mounting, since the front would now be held in the cabinet and the rear supported by the chassis. It used to all be supported by the chassis, not a good scheme with that flimsy plastic thing.

Still waiting to hear about the 9-T-79, I hope to have those details ironed out in the next few days. If/when it gets here, I will evaluate them both and make a decision about which will become the new home for this set.

http://videokarma.org/attachment.php?attachmentid=171593&d=1315638407
http://videokarma.org/attachment.php?attachmentid=171594&d=1315638407
http://videokarma.org/attachment.php?attachmentid=171595&d=1315638407
http://videokarma.org/attachment.php?attachmentid=171596&d=1315638407
http://videokarma.org/attachment.php?attachmentid=171597&d=1315638407

If the only thing stopping mounting the unmodified porto chassis/CRT combo in the cabbinet is that back board near the top of the cabinet then why not cut it out of the cabinet to make way for the proto chassis?

Proto chassis fits like a glove, not even an inch on either side

Just wondering . . . .

I've never handled a C-73547, but depending on who made and when they made your cabinet's original 19AP4, it is 4 to 5 inches shorter than a production 15GP22, so when you add a couple of inches for the deeper early CRT socket, just how big is your bucket going to be?

Jas.

Tom,

That board in the back is removable I think, but it's not keeping me from using the cabinet. The problem is that the mask is secured to the cabinet, where it was attached to chassis before. Because the CRT mounting is now split between the cabinet and the chassis, some means of supporting the CRT from the rear will be required at least while the chassis is removed. I may be able to make up a bracket that hangs from the top, since that's how it originally worked when this thing was B&W.

So instead of using the proto chassis' original front mounting you are using the one from the monochrome set's cabbinet, or are you changing the the way the original proto set's front CRT mount from being attached so that it is mounted to the cabbinet instead of to the chassis as I beileve it originally was (only reason I can think of for the latter would be if the tube is too far back on the chassis to look right through the mask)?

Sorry for all the questions. I'm a bit confused as to what you plan to do with the cabinet.

Tom C.

I think you have that right. The problem is that the way is was originally had the tube at a funky angle, so it would have left gaps in the front of the set between the mounting bezel and the front of the cabinet. If it turns out that it's not possible to do this the way I want to, I can always just keep it the way it was and deal with the gaps.

If i were you I'd keep the CRT mountings as they were originaly. The possibilities of stress/breakage that come form sitting in, and mounting/unmounting the CRT in a setup that supports the front of the tube with the cabinet, and the back of the tube with the chassis frighten me. It is your set so do what you want, but if I were you I'd avoid doing that with a prototype CRT that is worth a few grand and which is one of only a handfull of survivors (though something like a 10BP4 or a generic 50's 21" I'd consider subjecting to that risk).

Tom C.

If I do keep the CRT supports all on the chassis, I would have to get a new set of narrowed support arms for the side. Perhaps that's the easiest thing?

If I do keep the CRT supports all on the chassis, I would have to get a new set of narrowed support arms for the side. Perhaps that's the easiest thing?


I think that is an excellent idea, provided you have the round brown Bakelite(?) front support which was visible in Harry Poster's pictures, but not in your pictures.


I suspect that these brown and/or black brackets were actually used as part of the screen mask on the earliest prototypes.

Look at the color picture of the two color sets in the March 1950 RCA demonstration to the FCC (near the bottom in this link which shows very dark masks):

http://www.earlytelevision.org/color_prototypes.html

My guess is that one of the estimated 35 model (circa 1950) model No. 1 Receivers and Converters (modern term: monitors) was re-purposed for the newer system and this is the reason why there are so many joints in the chassis as they recycled parts and complete circuits from the old units.

http://www.earlytelevision.org/rca_model_1.html

This theory would also match the date on the tuner. If you notice the picture, this model uses strait support brackets. The uneven bends on your brackets could stem from the time that this set was converted from a (circa 1950) 16 inch CRT to a (circa 1953) 15 inch CRT. If anyone knows the bell-bottom dimensions of the 16 inch 1950 prototypes, this probably could be confirmed.

http://www.earlytelevision.org/rca_color_prototype.html

In the top right photo, notice how the HV cage in the converter is placed on the right (when viewed from the rear.) If you had a cage, it would go directly behind the crudely bolted on upper control panel.

Also notice how the left side of the receiver chassis (again, when viewed from the rear) has what seems to be the tuner side of the set below bolted on with similar tube placement. Also they used apparently identical CRT supports to your set on both model 2 and 3.

To me, all these indicate reused parts.

James.

Brother dropped off a connector for the power supply inputs, but I still need a backshell for it. It's really tight, so having something to grab on to will be a bonus.

http://videokarma.org/attachment.php?attachmentid=171612&d=1315802007

The two prong plugs in the back ground were used extensively on early post war Webcor magnetic audio recorders. I even have spare two prong plugs and a socket if you need them.

I could use a single female one.

Hi NIck,

I have a new shell for the connector. I'll put it in the mail to you today.

Steve

Thanks, Steve! :beerchug:

Fascination overcomes me after reading through this entire thread. Really great documentation of your progress so far-- I cannot wait to see the outcome. It is truly awe-inspiring to see these pieces resurrected after countless decades of in-operation. You already know this, but you've got a very unique piece of crt history there.

My only hope is that the chassis can be made operational again, then we will see what the engineers saw around 1953! To do that, we need to make certain what signal to pass through it. Best guess right now is CPA with the higher subcarrier frequency, but without the entire circuit being traced I'm still in the dark. Tim is still working on getting the electronic version ready, it's hard to find time what with just graduated and getting his first 'real' job.