Newbie's First Questions RCA TS 721 Restoration

[Chris K]

Originally Posted by Notimetolooz

Although not shown in the picture you posted, if you follow that line it goes to the grid of the sync amp through C120. The grid of that tube should be biased with -3.5V, if C120 were shorted the resistor junction wouldn't be that negative unless the -3.5V supply was much lower. I could believe -1.5V at that junction but not -15V. Double check that supply.

What your meter would measure as the DC value of the video signal depends somewhat on what the pattern is on the video signal. It is possible that your meter is confused by sync pulses on the video. The video signal could be as large as 32Vpeak-to-peak according to the scope trace on L106. Many times the voltages on schematics are with no input signal, also note the control settings.

I don't have any definite explanation at this point.

Since modern solid state electronics generally run at lower resistances a leakage like a 1Megohm across a cap would not cause much of a problem, but in a tube circuit it would. Those caps you got cheap might work OK in a solid state circuit.

I will double check the voltages and provide a better overall picture of the issue later this evening. Thanks for your thoughts...as always!