RCA CTC-12 estate sale find

[frenchy]

Adam, are you doing an immediate test of the gun strength after turn on, or letting them warm up for 5 minutes or so? The test of a good tube is if it meets the numbers after 4 minutes of warmup. My ctc-11 is definitely dim when first turned on but comes on full blast after a few minutes. I think that was a partial reason they had put a brightner on the set years ago. The more I use the set, the stronger it is when I first turn it on, so it seems when the set sits idle for quite a while it starts going back to being noticeably dimmer when first turned on. Doesn't bother me and I took the brightener off. Maybe your bottle could use some longer on-time to wake it up some more, 3 months is a long time. (I said 'bottle' so I sound more like a old pro, heh heh)
I don't think the filaments are anywhere near each other, but they can short against other parts of their particular gun though.
Frenchy

[blue_lateral]

If only one of the three filaments doesnt light, that is an open circuit, not a short. The tube is bad. I have one like that, also on green.

John

[Adam]

I had left out what I think is an important bit of information, when I had first turned on the set, after it had sat for 3 months, there was a spark inside the crt neck, like when you hit the red button on the rejuvenator. Whatever it was is what I think may have lowered the emission of the red gun, the green and blue seem unaffected. The 1/4 way up the meter for the red is after its been on for about 5 minutes. Anyway, I have b/w sets that only register that high that produce a bright enough picture, even though the tester puts it in the "bad" area. And I have some color brighteners, too.

I think my major all green problem is caused by these funky grid voltages, seeing the green is way too high and the others too low. I checked the 2 resistors between each of the grids and the 400v supply, they were all good, it's almost never something easy to fix that'swrong with these sets.

[Steve D.]

Originally Posted by Adam

I stayed up late last night and changed the electrolytics. The picture is full size, but it is still all green. There is a little blue, but no red at all. I checked the 21FJP22 again, and all 3 guns are good. I tried the setup mode, all I get is a 3/8 inch thick green line, even with the green turned all the way down and either red or blue or both all the way up. I tried to put a color bar generator on it just to see what would happen, it was all green, but what was interesting was when I turned it to show the crossed lines, it would show me the white lines (becuase of the little blue it has), but the background which should have been black was all green. And this is with the green screen and drive controls set all the way down. The brightness control, tint control and color control have almost no effect on the picture at all.

Adam,
I'm not an especially technical type but do refer to my trusty book " Coor TV Servicing Made Easy." 1964 edition. Your CTC-15 chassis is somewhat similar to the CTC-12 so this may help.

Check #2 in the following list, this may have already been addresed.

The CTC-12: "No Color"

1. Check color killer adjustment.

2. IF THE 3.58 OSCILLATOR STOPS, THE COLOR WILL BE VERY WEAK, AND ALL AREAS THAT ARE SUPPOSED TO BE IN COLOR WILL BE GREEN, iF YOU USE THE COLOR BAR GENERATOR, ALL BARS WILL BE GREEN AND THE TINT CONTROL WILL HAVE NO EFFECT.

3. Check the bandpass stage, in the usual way, for bad tubes and wrong voltages. For shop repair, tune in a keyed color bar generator and follow the chroma signal through the various video and bandpass stages with a scope.

-Steve D.

[blue_lateral]

Originally Posted by Adam

Adjusting the screen controls, the voltage there varies between 400 and 1000 volts on all 3 guns. Seems ok. An unhappy development, I tested the crt again, 3 months ago the green and blue guns read 3/4 of the way up the meter and the red 1/2, now the green and blue are the same, but the red only 1/4.


I'm still worried about my red gun, but at least I found what seems to be the problem, the grids are all off, green = 400v, blue =100v, red = 50v. They're supposed to be 160v.

Plate voltage is 300v on all guns (it says it should be 345v), I wouldn't think this is a serious problem.

I was just looking at the schematic and the grids are fed with the 405v tap, through the 22k plate resistors for the r-y, g-y, & b-y amps. For the green grid to be at 400v, the plate of the g-y (6gu7) amp would have to be up there too. The plate must not be drawing any current. Could that tube be bad?

[Adam]

Recent developments: The wire connecting the 400v to the red and blue was broken, I changed it, now green and blue are at 350v, red is at 190v. I have all 3 colors on the screen, but the color is all wrong. Tint and color controls are still completely inneffective.

Last night the crt socket got loose and would only work if I held it, so I took it off, it wasn't hard to get off (none of the wires were broken some just must have come loose). I spent about 8 hours trying to put it back on, finally what I did was to thread some solder through the pins of the base, then solder the solder to the wires, then it just pushes right on, and you use the solder to solder it back.

I tested all the tubes and replaced the bad ones a while ago. Now I had replaced the 6GU7s with 6AX8s, I happened to have them and one of those tube substitution books said it would work. Thanks for the ideas, I will check more of this out later tonight.

[Adam]

Well, you can NOT substitute a 6AX8 for a 6JU7. I was looking at the voltages at the G/Y, B/Y R/Y amp tubes and they were just wacky. So I looked up the 6AX8 in the RCA tube book I have and it turns out it is not even a dual triode like the 6GU7, it's a pentode. I can't find the book I was looking at before, I do remember buying them about a year ago because I found them cheap and I remembered reading that they would exchange with 6GU7s. Anyway, I had 2 used 6GU7s and I put them in instead, and they work great.

No problem at all with not enough red, I just have the red screen control a bit higher than the others. I think also it had started reading really low due to loose wires in the tube base. I am now having problems with the socket in my color crt tester, so I can't test it to see if it went back up after I resoldered the base, but seeing it isn't a problem, I guess it doesn't matter. I only wish I had thought to glue the base to the tube when I put it back on, it works, but is loose, but then I really don't want to take it off again.

It still needs plenty work, the wire fuse for the tube heaters burned out, and I just twisted it together so I could continue to work on the set, but should replace it. The convergence needs to be done, and this will be my first attempt at doing that. And I need to change the electrolytics in the power supply/amp at the very least to get the stereo to work. And one of the legs is broken off.

[Adam]

I turned the set around to watch it for a while, and the picture tube got magnetized. I don't know what did it, I didn't move it in close proximity to any big speaker magnets or anything. Anyway I don't have a degaussing coil, but just read on an old post here that you can use a soldering gun, so I think I'll try that when I get home tonight.

Also, when I hook it to the dvd player, if I adjust the fine tuning to get the color right the sound buzzes, if I adjust it for the sound I only get b/w. With an antenna, and not such a strong signal, this isn't a problem. Is there something I can put between the dvd and the tv to cut the signal strength a bit (without giving me a snowy picture-I tried a few resistors and that's what happened), or am I going to have to attempt to realign the sound IF section to fix this?

[blue_lateral]

Sounds like AGC overload. Try turning the AGC control down until the problem disappears. Back then you would have just set this on the strongest station. Turn the AGC up until the picture just starts to shift, or the sound goes wonky, then back it off just a little.

John

[Adam]

This is with the AGC already set all the way down. With the AGC all the way down, and the fine tuning set just before the color goes out, the buzzing mostly goes away, but with the AGC up just a little the color looks quite a bit better.

[blue_lateral]

Oh. Well, you may have to do sound alignment. The good news is you use live sound for the source, and a VTVM. Sounds pretty easy. The factory procedure is wanting a "sound detector probe" though. I dont know whats in that one. I'll bet a regular detector probe would work. I'll dig a little deeper.

Set the AGC on your strongest signal source. You should be able to turn it up until the picture "shifts" suddenly, probably down and to the right, then just back off a little.

[blue_lateral]

You could first check for a problem with the sound detector diode by checking from point "b" to ground with an ohmmeter. Should be about 10k one way and about 2.5k with the leads reversed. Bad tubes could cause it too. Anything to make the sound IF signal weak

Ok, heres a non-factory procedure from Carl Babcoke's "RCA color tv service manual". You'll need a couple bias boxes. 9v batteries and pots could suffice in a pinch probably. Bias is always negative here.

(1) Adjust the fine tuning to any point that gives clear sound without buzz or noise, even if this point results in sound bars or a beat pattern.

(2) Adjust t203 (the sound detector transformer) for maximum volume and minimum distortion, using the second peak from the top of the coil.

(3) Apply a fixed bias of around -3 to the tuner AGC and approximately normal bias to the sound IF tube.

(4) Adjust the fine tuning for minimum buzz, then increase IF bias until the buzz and noise *barely* appear again.

(5) Now adjust the take-off transformer, t201, and the sound IF transformer, t202, as needed to eliminate the noise.

(6) Any time a transformer adjustment clears up the buzz and noise, increase the IF bias until it barely re-appears.

(7) Adjust the sound IF transformers again, then increase the bias until a change either way in the transformer cores makes the noise start again.

(8) Remove the bias supplies and adjust the fine tuning normally. Once more adjust t203 for maximum volume with minimum distortion.

(9) Try the fine tuning over a wide range, for a normal sound circuit with accurate adjustment should result in good sound without critical fine tuning adjustment.

I havent attempted this in a long time. Your mileage may vary.

.

[Adam]

A loose IF tube was the cause of a lot of the trouble, and cleaning the volume control helped a bit. But I still have the AGC nearly all the way down, and there is only one exact spot on the fine tuning dial that is buzz free with good color. So I think I will give the allignment a try before I put the set back together for good.

The soldering gun degausser worked, but it took quite a few passes, and it's still a just bit greener on the very top and the bottom right.

[bgadow]

Originally Posted by blue_lateral

Ok, heres a non-factory procedure from Carl Babcoke's "RCA color tv service manual".
.

That's one of my favorite books on color tv repair. The writer is a real straight-shooter. There was a copy on ebay the other day.

[Adam]

I did the convergence, and the color is really good now. What I thought was a still slightly magnatized tube was just the purity magnets misadjusted. As far as the sound allignment I only needed to go up to step #2 to fix it completely, but thanks for writing up the whole procedure. I'm might take a look around for a copy of that color tv book, my tv repair books are all b&w.

The vertical output transformer is quite noisy, I worry it might be going bad, but then there are no problems at all with vertical deflection.

Now I just have to replace that fuse wire, unstick the uhf tuner, and deal with the stereo. I have all these big tv and radio consoles, but its just what I keep finding, if I had my way, I'd rather be done once I just fix the tv and not have such a huge console, and I like working on the radios, but I have never done too well with fixing record players, they always wind up playing too slow, even after I clean the motor.