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......

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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!

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.

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:D

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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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.

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:smoke:
LFOD !

Is a 6GH8 and 6GH8A the same?

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. :thmbsp:

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.

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:thumbsdn:

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 :D

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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.

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.

QUOTE=TUD1;3199299Don'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.

Very nice set. My friend's mom had the exact same set, and it had a great picture and sound.

The 6GH8 was RCA's "Milestone Tube"!
The OEM 6GH8's used in the last tube type RCA's, the RCA logo was printed in white.

I always found GE tubes to be least troublesome. I agree about RCA, I had better luck using a 6U8 in an RCA anyway.

I didn't get time to mess with it last night, slaving away printing photos in my darkroom for mother's day haha.

The top priority is to get the color to stay, I think it was goofing up my attempt to set the purity, as I got no red screen when I set the switch on the back to "raster" and turned off blue and green. And my blue lateral adjuster and purity rings seemed loose and sloppy


More to come.........

You're off to a very nice start. CTC 21 what year would that have been? Your jug looks very good. Almost like it were a very low used set. I remember taking those big heavy sets out of basements when I was in my teens. Man, that weight did a job on your hands after you got it out of a basement and loaded into a truck. I changed quite a few flybacks in my day on RCA's. Zeniths seemed to have good flybacks, but the triplets would go especially in a home that had smokers. That tar would coat everything in the chassis. We always cleaned the screen of every tv serviced. It always brightened up the picture.

I believe the set is a '67 model. I got around to cleaning the controls and have a better, more stable picture now, got the color killer pot cleaned so it seems to stay in color now, I found a 10 uf 350 volt 'lytic cap under the color demod board and replaced it. Purity set up, static convergence is much better now, but the dynamic leaves a bit to be desired. I can't find a schematic online so I might hit up my local library to see if they have any Sam's books there.

The sound is a bit scratchy, that volume knob pot is hard to get to. All the sound circuits on this appear to be solid state and it looks like the amp part of this beast has a separate power supply (also solid state)

The library doesn't have any Sams.

I tried to look up the number on that diode pack on the convergence board and got nothing. Anybody got a pinout on that?

Also whats the deal with the motors on the back of the tuners? I don't think this model had a remote......

Check the early television museum for that schematic.

Did you already look to see if it is or isn't there? (It isn't). You are sending him on a wild goose chase.

http://www.earlytelevision.org/tv_sc...ams_color.html

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Chances are, the set was equipped with a remote control, as the manual tuned sets didn't have motor driven pots on them. Some of the manual tuned sets did have a motor driven tuner, but that's about it.
I don't remember where the remote receiver was located. Maybe on the TMA or mounted on the main chassis. :scratch2: Another senior moment. :sigh:

That's why I said check ETF , for him to check to see if it's there. If I checked already myself and it was there I would have told him it was at the ETF. No goose chases.

The point I was trying to make is if you had checked yourself, he wouldn't have to.

Sometimes it's just makes a whole lot of sense to check yourself first rather than give a blind lead to someone. It was probably quicker for you to have checked the ETF site than it was to type in your post. Took me less than 10 seconds to look and see it wasn't there.

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Guys, guys, simmer down, no goose chase here. ETF only has roundies.

I fixed the scratchy sound, there's a 3 pin connector near the power transformer on the chassis that was dirty.

As for the lack of a schematic, that is motivated by my cheapness, Sam's wants $22 for a single folder (881 folder 3 in my case).

Look for an online outlet selling second hand original hard copies. The quality will completly beat the official Sam's and usually one quarter the price.,

I sucked it up and got a digital Sam's. I replaced that pesky diode pack with discrete silicon diodes and BAM! nearly perfect convergence :banana:

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Man, that looks like factory condition to me. Good!

Ok, so why did the 6GH8 suck so much, and how come if they sucked so much, did RCA and everyone keep using them?

I don't know, but comparing schematic voltages and calculated plate dissipations to the GE spec sheet, It seems like the pentode section was pushed rather hard in some of the sockets.
The burst amp in the CTC-20 shows a plate voltage of 385 v, but the GE spec sheet says the max rating is 350.

In the CTC-12, the pentode section in the chroma oscillator appears to have a plate dissipation of 2 watts (spec max = 2.5w). In the few sockets I checked in the CTC-20 6GH8 "forest", it appears the plate dissipation was about 1.5w.

Not sure why the plate voltage and dissipation was designed to be so high, because, unlike a triode, a pentode's AC gain is mainly affected by plate current, not voltage.

I guess these tubes were just used too close to their design limits, but by using multitudes of them, the cost to the factory was probably reduced.

On the 6GH8 subject, Last time I went to my local surplus store they had a bunch of em, mostly RCA. I noticed some of them were marked "Brazil" as the country of origin. I wonder if that is one of the factors in the reliability of this tube? Thankfully this set (CTC-21) only uses one 6GH8.

*Update*

The dreaded black bars showed up in the picture last week, symptom of 51 year old filter capacitors. So an order in to Mouser for a bunch of capacitors, pulled the chassis and did the recap, powered up, no smoke or flames :banana:

not to mention a great looking picture! (I'll touch up the convergence later)

More to come as I was recently gifted a Dual 1019 changer (original was missing!). The ultimate 1960s audiophile/videophile console!

Your dial indicator lamp looks a lot brighter than the photo that had it on channel 9. Did you replaced the dial lamp? Set is looking nice.

No, same bulb. The AFC knob when pushed in dims/brightens the dial indicator lamp.