New project - Canadian RCA CTC 38

[maxhifi]

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.

[maxhifi]

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.

[mstaton]

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

[maxhifi]

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.

[DavGoodlin]

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.

[maxhifi]

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!

[maxhifi]

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.

[DavGoodlin]

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..

[maxhifi]

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.

[old_coot88]

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

[maxhifi]

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?

[DaveWM]

or 4...

[maxhifi]

Originally Posted by DaveWM

or 4...

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

[DaveWM]

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?

[maxhifi]

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.