[martin.m]

Update. The set has been running fine but has suffered from an annoying crackle when turning the volume control, even though the control has been dismantled and cleaned. On this model the grid of the UBC41 audio amp triode is connected directly to the wiper of the control. The valve is biased via a cathode resistor of 4700 Ohms. I don't usually modify vintage circuitry but I tried fitting a 470k resistor from grid to chassis and reconnecting the grid to the control's wiper via a 0.1uF capacitor. Result, a lovely quiet volume control. There was no DC voltage either on the top of the control or the grid of the UBC41 so I'm not quite sure what was going on. I'm going to leave it like that.