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  #1  
Old 05-07-2018, 08:58 PM
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mr_rye89 mr_rye89 is offline
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CTC 21 Console Aquisition

I grabbed it from the thrift store today, they were happy to take $20 for it. and it weighs a ton.

Aside from convergence, the picture is pretty good. sometimes the color goes, but is brougt back by messing with the fine tuning.

Signal is being fed by a BT agile modulator on channel 8. And the bars in the picture are from my camera.

The convergence seems impossible to improve, the pots are real scratchy and I cant figure out how to clean 'em......








Last edited by mr_rye89; 05-07-2018 at 09:11 PM.
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Old 05-07-2018, 09:13 PM
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Holy smokes! You lucked out big time! These CTC-21's are great sets, I've been trying to find one for nearly three years. The thrift stores here would never have something like this. Enjoy it!
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Old 05-08-2018, 12:29 AM
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Spray some de-ox-id under the edge that faces the board to clean the pots.

Protip: the diode packages on most deltagun sets even into the 70's was selenium, and can go bad. Replace with a few 1n4007s and convergence may improve, on the convergence board the caps may be worth replacing and the resistors are worth checking. The position of neck hardware can also screw with the range of the dynamic convergence.
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Old 05-08-2018, 09:39 AM
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Great $ave! RCA's finest tube-rectangular work IMHO.

I had the guts to one of those models, shop I was working for retrofitted and RCA 25" monitor and reconnected those speakers. The customer was thrilled, RCA no longer offered a cabinet that matched t heir furniture. I got to remove the leftovers

It worked right away when I put it in another early American maple cabinet and it was OUR college apartment set. Used it the whole summer of '82 to watch HBO-CINEMAX repeat movies, enjoyed in lots of company and everyone was amazed it was 15 yrs old.

I miss it terribly, as fine an example of RCA's last good tube chassis as any made. The color and video were just perfect. I sold it for rent money in fall semester, got a 69" Zenith again when I got another TV shop job.
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Last edited by DavGoodlin; 05-08-2018 at 09:42 AM.
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Old 05-08-2018, 03:14 PM
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Is that funky thing towards the top left corner (of the convergence board) a selenium diode pack?

I also figured out the static convergence last night so I got a much better picture. I'm just learning about delta gun CRT setup.

There's something about the color on these old sets, It's almost like Kodachrome............
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Old 05-08-2018, 05:24 PM
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Quote:
Originally Posted by mr_rye89 View Post


Is that funky thing towards the top left corner (of the convergence board) a selenium diode pack?

I also figured out the static convergence last night so I got a much better picture. I'm just learning about delta gun CRT setup.

There's something about the color on these old sets, It's almost like Kodachrome............
The light green rectangle on the lower middle left is your diode pack. If you're new to doing delta-gun convergence try redoing it a few times before blaming the set...it takes time to get good and used to it. I think I redid it 3-5 times on my first attempt before I was satisfied.
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Old 05-08-2018, 05:47 PM
zeno zeno is offline
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Very strong CRT. The conv problem is mostly center conv. When you
get the center good the edges will follow. All the controls on the conv
PCB are wire wound so they feel "scratchy" compared to to regular
carbon pots.
For the color first turn off AFT or AFC if it has it then put back on after
fine tuning. You can also turn the color killer control all the way off.
The set uses a bunch of 6GH8 tubes so pick up some of those NOS, they are
nothin but trouble. The 6GH8 & there sockets were the biggest fault of
these sets !
You are off to an excellent start with this one, nice buy !

73 Zeno
LFOD !
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Old 05-08-2018, 06:47 PM
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Quote:
Originally Posted by zeno View Post
Very strong CRT. The conv problem is mostly center conv. When you
get the center good the edges will follow. All the controls on the conv
PCB are wire wound so they feel "scratchy" compared to to regular
carbon pots.
For the color first turn off AFT or AFC if it has it then put back on after
fine tuning. You can also turn the color killer control all the way off.
The set uses a bunch of 6GH8 tubes so pick up some of those NOS, they are
nothin but trouble. The 6GH8 & there sockets were the biggest fault of
these sets !
You are off to an excellent start with this one, nice buy !

73 Zeno
LFOD !

Is a 6GH8 and 6GH8A the same?
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Old 05-08-2018, 10:18 PM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by zeno View Post
Very strong CRT. The conv problem is mostly center conv. When you
get the center good the edges will follow. All the controls on the conv
PCB are wire wound so they feel "scratchy" compared to to regular
carbon pots.
For the color first turn off AFT or AFC if it has it then put back on after
fine tuning. You can also turn the color killer control all the way off.
The set uses a bunch of 6GH8 tubes so pick up some of those NOS, they are
nothin but trouble. The 6GH8 & there sockets were the biggest fault of
these sets !
You are off to an excellent start with this one, nice buy !

73 Zeno
LFOD !
IIRC, the CTC21 only has only one 6GH8 plus a 6KE8 in the color circuit.
It still good practice to have a few extras on hand.
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  #10  
Old 05-09-2018, 09:50 AM
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Quote:
Originally Posted by TVTim View Post
Is a 6GH8 and 6GH8A the same?
Generally yes and 6GH8's are descendants of the 6U8 and 6EA8. There is an article I need to find on what was "improved" on the -A, possibly only improved filament warm-up time, as they were used in some series-wired filament (transformerless) TV's.
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Last edited by DavGoodlin; 05-09-2018 at 09:54 AM.
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Old 05-09-2018, 09:53 AM
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Quote:
Originally Posted by dieseljeep View Post
IIRC, the CTC21 only has only one 6GH8 plus a 6KE8 in the color circuit.
It still good practice to have a few extras on hand.
Thanks for the reminder Dave, I knew there was a reason this chassis stood out alongside the CTC25, 28, 30 and 35. The 6GU7 was a better color difference amp than the 6GH8's triode, and those 4-PCB chassis' proved it.

The CTC38 (and several before it) were consummate 6GH8-eaters
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Last edited by DavGoodlin; 05-09-2018 at 09:57 AM.
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Old 05-09-2018, 12:16 PM
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Yeah I only found one 6GH8A in the set, which tests good, I'm gonna check the solder joints at that socket and a few other places.

Now when I set up the purity, do I just feed the set a "blank" signal? I don't have a crosshatch/colorbar generator, Ive just been using the picture viewing feature on my DVD player, with various patterns of course.

In the mean time enjoy some badly converged Star Trek

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Old 05-09-2018, 01:45 PM
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If this set has a service/raster switch you can put it in "raster" mode, and turn the blue and green screens down until you get a full red raster. Degauss the set, then pull the yoke back and adjust the purity rings until the red blob is in the center of the screen. Push the yoke back and adjust greyscale with the switch in "service" mode, and you should be good to go.
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Old 05-09-2018, 06:18 PM
kvflyer kvflyer is offline
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And if you buy some 6GH8 tubes, look for NOS Sylvania. RCA manufactured tubes did not hold up. For that matter, toward the end, RCA bought the 6GH8 from Sylvania and rebranded it RCA because they were better.
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Old 05-10-2018, 01:28 AM
old_coot88 old_coot88 is offline
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QUOTE=TUD1;3199299
Quote:
...Push the yoke back and adjust greyscale with the switch in "service" mode,...
Don't push it back all the way against the bell of the CRT. You'll find the 'sweet spot' for best red purity to be about 1/8" to 1/4" shy of being all the way. This is true of all 25" rectangular CRTs.

With 21" roundies, it's about 1/4" to 3/8" shy for best red purity.
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