22-02-2017, 11:44 AM
Hi.
Looking at the phase splitter Andy I see you are feeding the cathodes from a negative supply, if those cathodes are decoupled (cant see your PSU arrangement) then the lower phase amp is probably the problem, it's cathode could well be shunting high frequencies but as I cant see the rest of the circuit I could be way off track. The -78v would need to be a high impedance feed and not decoupled at the cathodes.
Being as I am I prefer auto bias, seen too many amps go up in smoke if a valve goes into grid current with output transformers taking the brunt of the current. Bit like thermal runaway in transistor amps. Yes I do realise the down side of auto bias but it's just a me thing.
Looking at the phase splitter Andy I see you are feeding the cathodes from a negative supply, if those cathodes are decoupled (cant see your PSU arrangement) then the lower phase amp is probably the problem, it's cathode could well be shunting high frequencies but as I cant see the rest of the circuit I could be way off track. The -78v would need to be a high impedance feed and not decoupled at the cathodes.
Being as I am I prefer auto bias, seen too many amps go up in smoke if a valve goes into grid current with output transformers taking the brunt of the current. Bit like thermal runaway in transistor amps. Yes I do realise the down side of auto bias but it's just a me thing.
