unison simply four no sound

I own an origanal simply four tubes are glowing no sound any suggestions on this problem thanks


I've had similar experiences with other amps. Caused by a burned out resistor (in the bias circuit.) Something to check out if you're up to it.

Is there a time delay circuit that turns on the high voltage after the heater voltage? Something there could have gone bad such as a charging capacitor used as a timer.