Sylvania 336mu

[Electronic M]

Originally Posted by sylvania

I could of done that, I am using sound control pot to make it brighter which washes out most of pic i can still see it but very dim so I turn brightness all the way down. Contrast adjustment helps a little.Definitely AGC not responding I can turn it all the way right or left just get a little flicker at end of travel of pot. I have very good sound quality. Possible AGC
pot is bad it feels like it has no resistance when turned.

Is the 'sound control' still wired as a sound control or has it been substituted in another circuit?

If it is still wired in to only the sound system, then that behavior is both a significant problem and a clue......A large number of sets used what IIRC is referred to as stacked B+. Basically they connect the audio output plate to one of the highest B+ rails and use the tube as both a power amplifier and a power supply voltage divider resistor. The tube draws a fixed range of current (and variations within that get filtered out) and has a fixed plate and transformer impedance so it acts like a resistor. A lower B+ rail likely is supplied by the cathode of the audio output tube, and that rail likely feeds the video output tube, brightness control, and possibly the AGC circuit. If the audio output and driver circuits are not working just right then it can upset the cathode output voltage of the stacked B+ and disturb the circuits driven by the lower voltage rail it supplies....Troubles in the circuits driven may also cause problems. IMHO before you go after the AGC and brightness/contrast issues it would be wise to fix the 'sound control'/picture interaction (assuming the assumption made in the beginning of this paragraph are correct).