[Winky Dink]

Hum/buzz resolved. Finally got down to locating the source. Pulling tubes didn't help. I was advised that if C200 was disconnected and the hum persisted, that problem would be in that section. That localized it to the audio section. By luck, the first thing I did was disconnect C203. That stopped the hum completely.

After many unsuccessful trials with more and less capacitance, I finally realized what the problem was. Originally the 120VAC neutral went through the on/off switch; then to B-. C203 connected to B- at the switch. When I wired the hot side through the switch, I didn't change the C203 connection. C203 was connected to the rectifier filament/plate/dial light.