Oscillator off in RCA CTC-11?

[Phil Nelson]

In my RCA CTC-11, all of the channel frequencies seem low by about the same amount. The best tuning is found if you nudge the channel selector down a little and hold it. The difference seems present for all channels. This is outside the range of fine tuning. Adjusting individual oscillator slugs for a couple of channels didn't do the trick, either.

I suppose tuner components can drift with age, like anything else. I'm wishing there was a trimmer with a big red label called Master Oscillator, which I could tweak to move everything up a little.

The TV has great reception and stability otherwise, so I don't want to degrade that or force a realignment, which I'm not equipped for. It's more one of those annoying little things.

Ideas? Here's the tuner schematic for those who like to follow along at home.

http://antiqueradio.org/art/temp/RCA...rSchematic.jpg

Phil

[jeyurkon]

I supposed it could need an alignment, but have you tried adjusting A218? I think it will do what you want. Does the service manual mention it?

John

[Phil Nelson]

It's mentioned in the VHF oscillator alignment instructions, which tell you to adjust all the channels in descending order, starting with 13 (A218) and ending with 2 (A229). I figured these are the individual channel slugs which you can adjust through holes in the front of the tuner . . . .

Phil

[oldtvman]

Check the ground connections on the rf cable (had problems with those)

Clean the contacts in the tuner, oxidation can mask all kind of weird syptoms

If it's not those I would suspect capacitors.

It's pretty unusual for sets to go out of alignment.

[Phil Nelson]

Thanks, the tuner has been thoroughly cleaned & lubed.

The cable ground connection would be easy enough to check.

It's in the cabinet right now, but as I remember there is one mylar (maybe poly?) capacitor on top of the tuner case, C206. Part of the RF amp AGC, so I figured it's not involved here. The others are teeny ceramics inside the tuner.

Phil

[TV Engineer]

Did you try replacing the mixer-osc tube in the tuner? If so, try several for one that performs best.

Also, if memory serves correctly, there is a "master" osc coil on top of the tuner. Tweak it ever so slightly after ensuring that you have a good tube in the tuner.

While it is normal for IF and tuner alignment to drift in an old set, the change is usually slight and not very noticable. If your alignment is far off, it usually due to a failure in the chassis or inexperienced hands trying to improve things.

Good luck!

[jeyurkon]

Originally Posted by Phil Nelson

It's mentioned in the VHF oscillator alignment instructions, which tell you to adjust all the channels in descending order, starting with 13 (A218) and ending with 2 (A229). I figured these are the individual channel slugs which you can adjust through holes in the front of the tuner . . . .

Phil

I think that's why they have you start with A218, it will affect all the other channels when adjusted.

And I agree with tv_engineer that trying a different oscillator tube may help.

John

[Phil Nelson]

Originally Posted by jeyurkon

start with A218, it will affect all the other channels when adjusted.

I see the logic. There are access holes in front of the tuner for channels 2-12, but not 13 (A218). Perhaps that is their wily scheme to keep dolts like me from misadjusting things too badly before the serviceman arrives

The tuning for channel 13 looks dead on. If the tube swap has no effect, I can work my way downward from 12 and see whether things change for lower channels, which are the only ones I use, anyhow.

Phil