New project - Canadian RCA CTC 38
 

As the subject line says, the Ford hauled home a new project last night. Cabinet a beautiful and chassis looks original, even the tubes look original. It is spotless clean inside and outside, and has a service sticker on the back from 1970. When I got it, the seller said it had sound but no picture, and it was true. I heard the whine of the flyback and saw the CRT filaments glowing and took a chance. When I got it home I saw the high voltage lead had fallen off the CRT... Connecting it gave me a picture that filled the screen.

The horizontal hold control is very critical and becomes more so the longer the set is on, until after about a a
Half hour it is nearly impossible to keep a picture locked in. Also, there is a wave in horizontal lines on the screen. Will attach photos soon of my first RCA.

Played with the TV a little bit this morning... it works great until it's fully warmed up, then the picture has trouble staying in sync. Can bring the picture back with the horizontal and vertical hold controls, and fiddling with fine tuning, but all are very critical adjustments and don't seem to keep it for very long.

Also, the picture seems to get dim with poor brightness and contrast as the set warms up - starts up bright and crisp though. The horizontal wave is more minor than I originally thought, the linearity is actually not bad all things considered.

If this were a stereo amplifier, my next step would be to clean the controls, test the tubes and replace all the electrolytic capacitors. This TV also has some of the green and brown capacitors which look like Sprague orange drops, and I have read they can be suspicious. The tuner appears to have one Nuvistor rather than two tubes like my other TVs. I should correct my above message, this is not my first RCA, it's my first COLOR RCA.

Most if not all RCA(from the early 60's) color sets had nuvistor tubes in the tuner kind of like Fisher 500C's. They were called "NewVista",a play on words until the all transistor tuners came along and those were called "TransVista". Watch out for shorted 6GH8's. There are plenty in there

Does a shorted 6GH8 usually show up as bad on a tube tester? Which section typically shorts? I am pretty sure I can test all the tubes on my eico 667, including the nuvistor.

That horizontal wave could be the result of a heater-cathode leakage in one of said 6GH8s, pretty sure your EICO would show that.
I have an EICO 635 simple emission tester, which must be older than yours, that usually catches shorted 6GH8s.

I have a TV-7C tube tester too, but it can't do compactrons so is less useful for working on TVs. That would be awesome if the TV can be made to work well with only a few new tubes!

Update:

Removed the control plate and cleaned all the controls... removed the tuner assembly and cleaned the tuner. Am surprised to see a wafer style tuner instead of turrets like on a Zenith, it seems kind of cheap.

Tested most of the tubes. Found one weak pentode section in a 6GH8 - replaced it. This TV has very low hours, a handful of tubes were replaced in 1970 and all of them still test almost new. All of the tubes the TV came with are RCA brand.

The only dust in the entire cabinet is stuck to the tubes in the high voltage section (focus rectifier, etc)

So on to the problem - the TV warms up and makes a beautiful picture... my Zenith of similar age could never make such good colour. However after it has been on a little while, it loses sync and the picture gets scrambled, looking like someone has turned the fine tuning control too far. Adjusting the fine tuning will bring it back, but not for very long. Sound is perfect and almost completely free of buzz. I am thinking it could be AGC related somehow, but don't really know how to go forward aside from getting the correct sams service data and starting to check voltages and waveforms.

There may be an issue with the AFT (automatic fine tuning) voltage drifting.
I will look in my RCA service manual.

Maybe a can of freeze spray would find the problem part. I don't remember RCA's tuners being much trouble, but none had turrets like the Mags, Zeniths and others..

Hmm that makes sense. The problem occurs weather or not AFT is activated though, although I am not sure how much of a difference it makes.

Basically the sequence is like this

1. Scrambled image with great sound
2. Turn off AFT, adjust fine tuning until image appears, then turn on AFT
3. Go sit on the couch and watch 30 seconds of TV (works a bit longer before TV is fully warmed up)
4. Image returns to scrambled version... and by scrambled I mean as though horizontal hold has been lost, still good sound
5. Back to step 2

If I skip turning on AFT, the result is more or less the same. Have tried channel 3 and 4, and also UHF with different modulators, all behave the same way.

Also, after a blank screen is shown, the picture rolls a bit and sometimes vertical hold needs to be adjusted to get it to stay in sync.

Also, during the 30 seconds the picture stays in sync, the horizontal and vertical hold controls seem to work properly - i.e. there's a dead zone where the picture remains stable, they're not overly critical in adjustment.

Maybe the above clarifies the problem a little bit - thanks for reading and giving some input, I think this RCA still has a lot of life left and I am excited about using it regularly.

Have you subbed the mixer/osc tube in the tuner with a known good one?

The tuner only has the one tube in it, a 6DS4 Nuvistor. I tested it on the Eico 667 and it tests strong, but I don't have a spare. To be honest I am not sure how it works with only one tube, I need to have a look at a schematic - maybe it has a transistor or two in it as well?

or 4...

Now that makes a little more sense... not so easy to substitute though!

does it ever settle down?

Sure sounds like the AFC to me acting up. maybe you can confirm there is not correction voltage going to the tuner with the AFC off?

does the AFC have any pull in ability?

I think that makes sense, because if AFC was working properly, I wouldn't need to keep adjusting the fine tuning myself. I think I am at a stand-still until I get the schematic diagram and can get an understanding of how the AFC system works so I can troubleshoot is properly. I should make a short video of the TV doing its thing in case I haven't described the issue very well.

More time with the tv - I only had one 6gh8 in my tube stash and used it to replace the weak one I found yesterday. Tonight for fun swapped the video and sync 6gh8s which both tested good. Now I have a stable picture and noise on the video. Going to put a want to buy Ad for a sleeve of five 6gh8 tubes... These Are living up to their reputation! Tv is awesome though thanks all for contributions!!

Still want to see some video!

:thmbsp:

Some photos

iPhone is making me post these one at a time for some reason

Didn't bother to make a video yet but will do when I have free time, pic is still a bit wavy at the top. Lack of buzz in the sound kind of amazes me I never knew old tvs could work so well

Wow, that IS clean. Takes me back to my youth when I saw lots of these.
I had a CTC38XAH in a metal cabinet. Squarish VHF knob unlike yours.
We loved the tilt-out controls on those.
The sync was touchy as I recall but it made a very nice picture and the tuner was definetly better than the GE, Motorola and Magnavox sets of the same vintage.

I was watching Netflix on it last night and it is almost shocking to me how well skin tones are displayed once you dial it in properly, I was watching
This crappy documentary about someone who found alternate meaning in the movie the shining - the scenes they showed from the movie were like photographs on the screen, this tv is a major upgrade from my 16 inch chromacolor portable in terms of performance.

This is a 16 x 9 program, can see the bend at the top of the screen I mentioned earlier

Looks like Top Gear. Looks like you need to adjust your pin cushin

[QUOTE=mstaton;3090158]Looks like Top Gear. Looks like you need to adjust your pin cushin[/Q

Good idea! I was thinking capacitors but this really helped

Good score, that sure is a very nice looking and low hours CTC 38! I have two CTC 38s one working, one not yet :-) The working set I have, is in a nice, Italian provincial style cabinet, both are 25" with 25XP22 CRT' s.

I found out that I actually have a spare chassis for my new TV, which is awesome... got it a couple years ago with a bunch of stuff from an old TV repair man I bought my Silvertone roundie from, so I am covered for a significant number of the harder to find repair parts. To be honest I don't really like watching the roundie as much as the CTC38, to me the CTC38 is a "normal" TV, and I can watch it as though it's brand new, where I can never forget that the round screen Silvertone isn't giving me the whole picture.

I don't think the wave at the top of the screen is totally pincushion related, I got it looking better but it's still not perfect. It also has a little bit of a bend in the vertical direction, I am thinking the electrolytic capacitors are approaching design life and could stand to be retired. My 38 also has some purity issues (red looks a bit pink in one corner), and the greyscale needs to be adjusted. Once I get the Sams and a full new set of 6GH8 tubes I will pull the chassis and change all the electrolytic capacitors, then give it a basic setup - adjust purity, touch up static convergence check dynamic convergence (hopefully I don't have to do much with it!!), set grey scale and cutoff, adjust AGC and color killer, etc etc... I want it at its best.


Mine also has a 25XP22 CRT, I am very happy with the picture quality in general, aside from the fact it is old and needs a bit of a tune-up. I see a lot of potential though.

I am not sure what to call the style of my cabinet... I'd call it late 60s rec room, it won't win any design awards but at least the condition makes up for the lack of awesome design. I really want this TV to be in the living room but need to figure out where to put it so it doesn't make things look too junky.

I should have parts for that beast. Knobs, IF transistors, etc (OEM's)

It IS a beast... don't need any parts I know of right now, but that could change, so I will keep this on file. After Christmas it is going to get new electrolytic capacitors. It is operating quite acceptably right now, but red purity is lousy, and there's a bit of noise in the video from a bad 6GH8. There's a couple magenta blobs on the screen which ruin an otherwise nice colour performance too. Once it's up against the wall and not sitting in the middle of the room its a bit less massive and actually looks quite nice. I was trying to avoid doing a dynamic convergence adjustment but I think that its going to have to happen too.

You lucky dog. That is in as-new condition!
CTC38s didn't have such a great reputation, I've read. However the picture looks quite good from what I can tell.

Actually I loved the CTC38 and 39's. I knew most of the problems.

Bad news...I no longer have the schematics for them. It appears all i saved were CTC169 and upward.

As far as parts, I may have the fliter cans.

The TV has been doing a good job of entertaining me since I got it working... I have it connected to Netflix via Wi-Fi. I've wanted a tube RCA for a while and this seemed like a good one to jump at... I've heard from VK members that tube RCAs have superior colour to Zeniths and I wanted to check it out for myself.

I think I may want to pick your brain a bit - what problems are we talking about? Mine came with the high voltage tubes/horizontal tubes all replaced with 1970 vintage made in japan RCA red label tubes, which added up with the RCA factory service sticker from 1970 on the back of the set.

After watching the tv all year decided to give it some attention. I adjusted purity, convergence, and grey scale. Then I adjusted linearity and pin cushion. Man, does it ever make a nice picture now! I also replaced the nuvistor in the tuner,
which sharpened up the picture a lot. Only problem is the vertical position seems low (I.e. The black bar on the bottom of a 16x9 picture is narrower than the top bar when size and linearity are correct) and I have no clue how to adjust it. It's still got a bit of a wave as it did before, but I haven't changed any electrolytic capacitors yet. It's almost unbelievable how good the colour is now, it looks better than a lot of newer CRT televisions.

Also another question - an ideas what the blue knob just in front of the purity rings is for? (See pic)

Blue knob is blue lateral adjustment. CTC 38's had transistors in the IF stage go bad. They are 4 legged; ECG 161 was listed as replacement but were not a good choice if I remember correctly. The inverter transistors failed also. You will need #124754 and 124753 for OEM parts. I probably still have them. I hve never had to replace a nuvistor tube in a RCA tuner ever.

Hey thank you for the response !

I subsequently figured out that what actually removed the grain from the picture was not changing the nuvistor, as I thought, but disturbing the 300/75 ohm balun on the back of the set. It had a bad connection. What symptoms would result in needing those transistors?

My real concern now is how to adjust vertical centering. I noticed older sets have a control for this, but this one doesn't so far as I can tell.

Most common vert lin problem in most sets is the electrolytic
in the cathode of the vert out. In yours a 50 mfd 150V
its under the chassis near the damper socket. Its also in series with
a 25mfd in front most can.
The IF would cause no pix or snd or a very weak washed out pix.
Also common on the upright RCA portables & YES OEM best !
And yes nuvitars were reliable, think I only changed 1 or 2.

73 Zeno:smoke:

Would a vertical linearity problem extend to vertical centering ? So far as linearity goes I am pretty happy, although the height control I near the end of it's range.

I definitely have a great pic and buzz free sound, and there's plenty of contrast so I don't have a lot of worries about the IF. I am trying to figure out a convenient way to replace the four multi section capacitors without resorting to re stuffing them. Maybe a piece of perf board on stand offs will do it. I don't really care how it looks but it's got to work properly and not introduce any ground loops.

I will pull the chassis and change that cathode cap tonight, I Am pretty sure I have a new one somewhere.

I may have a new filter capacitor. It would be new old stock. I will look tomorrow. Wish I had part numbers in my mind....I think it may be 124791

Replaced the two capacitors, C7 and C2D. Both checked okay on radio shack multi meter for value. Still picture is a bit low on screen, and I noticed there's some choppiness to the test pattern at some settings of the linearity control, cleaning didn't seem to help. Here is the latest best effort convergence/ linearity. Notice the choppiness, some horizontal lines even doubling where they shouldn't.