Newbie's First Questions RCA TS 721 Restoration

[Chris K]

Originally Posted by Notimetolooz

I believe you said earlier that all the voltages on V105, a 12AU7, except pin 6 were correct, that would mean the cathode-grid bias is OK.

This thing began as a question why the intersection of R124 and R125 was -15V.
Up to now I hadn't investigated the math (Ohm's Law).

The math clue.
If one end of R125 is at +150 and the other is at -15V that means there is 165V across it. R125 is supposed to be a 1K resistor. The math says there would be a current flow of 165 ma. The wattage would be current times voltage and this comes to over 27 watts! That would burn it up for sure!
So if the voltages are right the resistance cannot be 1K.
The value of R125 is wrong or is bad or maybe a bad solder joint there.
Note that if one end of R124 is at -38V (V105 pin 6) and the other end is at -15V, the voltage across it would be 23V. R124 is supposed to be 3300 ohms. The current through it would be about 7 ma.

OK...I might have found it. First for your math, the -15V number I stated earlier was with current limiting through a bulb. The full 125V AC number is -36V DC between R124 and R125. But I just inspected the area closely and R125 doesn't look right. It looks a bit burned on the back side. It ohms out at over 55K! I'll replace and see what happens.