03-26-2014, 10:58 AM
If you are sure you have your filament current (can you see the filament glow when the tube is dark?) and your anodes (you do not have to have grid to have it glow) voltages and it is intermittent then it could be a bad tube with some intermittent separation inside.
Of course you have to exclude the possibility of bad socket connections etc.
Of course you have to exclude the possibility of bad socket connections etc.