TV-37 vertical hum?

[Electronic M]

You've probably considered this, but heater-cathode leakage in signal tubes can also cause this.

[miniman82]

Originally Posted by miniman82 in post #1

I swapped all the tubes around from another set thinking a H-K short was to blame but no dice

First thing I tried

[Tom Albrecht]

Originally Posted by miniman82

Went through all ground points in DC and AC looking for drops, couldn’t find anything. Tried 3 times to attach a scope shot, but apparently the forum changed what it deemed acceptable and now I can’t figure it out.

You may have to forgive me for beating a dead horse, but I’m not sure that looking for voltage drops is the best way to find a bad ground, unless you are able to see mV level voltages reliably. If it’s an aluminum chassis, I no longer bother to try to measure anything — I just wire all the grounds together with fairly substantial wire, since aluminum chassis can be so problematic for grounding. But if you want to measure something first, I’d check resistances to chassis, looking for anything over 1 ohm. Even mV level signals on a cathode can end up getting amplified to problematic levels.

Another specific place I recall seeing a bad ground in a TV-37 is the tuner, where some coils are grounded to chassis (or was it the band switch?). Caused one of the two bands not to work well. In this case, hum wasn’t the problem; RF performance was. Bad grounds on aluminum chassis can create all kinds of problems.

If all your grounds are under 1 ohm, then you can move on to looking for other causes.

[timmy]

Can you post a pic what it looks like ?

[dtvmcdonald]

I have one of those sets. It had that problem. The problem was a small heater-cathode leakage in sweep tube. I had a 7" set with a bar
(not sweep distortion) moving ta the usual rate, and was heater-cathode leakage in a tube affecting the AGC.

[Phil]

I had a problem almost identical with my tv-37. Eventually discovered it was a ground loop between the tv and modulator I was using. The balun didn't isolate it. I put small value capacitors on each side of the 300 ohm connection and the problem disappeared. At least it is an easy thing to try.

[dtvmcdonald]

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