Insufficient video gain in teletone TV-149

[Ralph S]

I'm just about done with a tele-tone TV 149 and have good sound but very low video gain at the picture tube (7JP4) though the DC voltages are correct. I've been through all the usual things: new caps and off-value resistors and crappy micas replaced. I tried pumping direct negative video into video/DC restorer stages and got good pictures, but video off the internal tuner is low and I think it's comes down to one or more open peaking coils on the video and later stages. Have any of you come across this problem with the Teletone line of receivers? I've never had it with any other make, except for the CT-100 RCA color set. Don't forget that the TV-149 is an intercarrier set and the sound quality and level are great AND the video at the plate of the video amp is good. What's going on here?

[miniman82]

Weak tubes? <shrugs> Could be any number of things, what's the scope trace of the video output tube look like? Can you drive it full white via input to the tuner, with a pattern gen or the like? If not look for bias issues, bypass caps that aren't up to snuff, or incorrect alignment. Also make sure you don't have a bad video tube; H-K short, grid leakage, ect. Just because the sound is good doesn't mean the video carrier is in the right spot, though 9 times out of 10 if video is good sound typically needs to be touched up. You can usually get close enough with a slope tweak if you know what you're doing, provided no parts in the IF chain were replaced...

[Eric H]

I have one of those and it has weak video too (weak contrast), I tried and tried to find a problem, swapped tubes, looked for drifted resistors etc.
If someone finds a cure I'd be interested in hearing it.

[Ralph S]

Thanks for the comments regarding video level on the Tele-Tone TV149. I've been through the set again this morning and have come to the conclusion that the trouble is primarily in the tuner. This particular one has had the detent mechanism broken by unknown means. In any case, the tuner is quite unreliable in positioning/indexing the channel positions and most likely the various sections of the Centralab style switching. So, I'm figuring that I have to be on the lookout for another Tele-Tone TV149 tuner which hasn't been "worked over" by unknown fingers during the last 65 years. Wish me good luck!