CTC-31 Color Problems

[drh4683]

6GH8's are and always will be noted (by me) as being the most unreliable trouble prone tube ever made. Definitly sounds like gh8 symptoms at this stage.

[bgadow]

Back at it again with this set. What can I say...I must really enjoy working on these sets because if I didn't I'd have tossed this one out the door by now!

I ordered a fresh supply of 6GH8's, nice NOS GE tubes. Replaced them all. The tiny amount of color I could get did look a little better but not much. To refresh (and maybe correct) with the generator hooked up and the agc cranked nearly all the way I can get color bars, nice and bright; off the cable tv though I have to back off on agc and I lose what little color I have as I get it where its supposed to be. I did some more probing, and so began the next chapter. I had noticed that adjusting the burst phase coil had no effect earlier when I was measuring voltages. Now I saw that pin 6 of the burst amp, which is supposed to see 355v, was actually seeing just about nothing. (less than 1v) I found that the coil was reading open. Pulled it, could see where there had been an arc. My clumsy fingers just made things worse. Checked with Moyer's-what an amazing place! Had 'em in stock, they were here next day! I got 2 in case this one gets fried, too. So tonight I put in a new one, no change. Hmmm....now I see that the peaking coil between the burst phase & B+ was open. I no almost nothing about these; looked around and found what appears to be a good replacement, though it looks different. (color codes are same, ohms read right) Soldered it in, now I have TOO much voltage-405. I also have another problem, maybe related to the high B+-arcing. A few chapters ago I had something arc on the board and I wonder if that might have been what killed the coils. This today arced numerous times, though I had trouble getting a glimpse of where at. Finally, just as I was turning the set off there was a tremendous (well, pretty bad) arc right underneath the burst phase coil! I checked and it still reads okay. I can't find anything obviously shorted (no solder problems, etc) so once again, I'm just left

Whaddya think, fellas? 50v too much couldn't be causing this, could it? And I wonder why its too high? Maybe I need a real match for the peaking coil? Any ideas? Oh, by the way, still no color

[Chad Hauris]

Too much plate voltage means the tube is not drawing current...check the screen grid voltage on the burst amplifier tube, also the cathode circuit.