[ms660]

I would normally check by measuring the resistance between the control grid(s) and HT -ve (chassis) and comparing with the resistances that should be expected according to the schematic, a bit out is usually no problem but miles out would be cause for further investigation even if it's not related to the present problem, the resistors used for the grid return to chassis are always high values (except the oscillator grid in comparison) and as such are sometimes prone to an increase in value from their original value over time so worth checking anyways.

Lawrence.