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PJL · 3rd Sep 2017, 7:03 pm

The forward voltage on the AGC diode suggests there is significant leakage somewhere - the question is where? Both V1 and V2 grids are connected without any series resistance so no help with diagnosis there.

Clean the valve sockets, valve pins and the wavechange switch which is very exposed in this model. Tapping each valve gently when the fault is present may also help you track it down. Failing that I would add a 10K resistor in series with V1 and V2 grids and measure the voltage across them under fault conditions.

3rd Sep 2017, 7:03 pm	#5
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Toaster FB10 elusive fault The forward voltage on the AGC diode suggests there is significant leakage somewhere - the question is where? Both V1 and V2 grids are connected without any series resistance so no help with diagnosis there. Clean the valve sockets, valve pins and the wavechange switch which is very exposed in this model. Tapping each valve gently when the fault is present may also help you track it down. Failing that I would add a 10K resistor in series with V1 and V2 grids and measure the voltage across them under fault conditions.