Winking Zenith Porthole

[Rob]

Michael,

I had a similar problem with my 1947 Admiral 30A13 chassis. It went away when I stopped trying to use rabbit ears in a fringe area and put a good strong signal from a VCR into the set. Your problem may be that the AGC circuit has an open time constant electrolytic capacitor and is motorboating due to slow time constant positive feedback. Without looking at a schematic the AGC is generally a common bias line that supplies the grids of at least the IF tubes, and sometimes the RF amp in te tuner as well from an AGC detector like a 6AL5. The grid resistors will not go to chassis ground in this case, but to a bus bypassed at each tube feed by a small disc capacitor.

Rob