Bias Question - Rookie Needs Guidance

[mikeboone]

I am working on a JCM800 2205 (repaired with much advice in another thread - THANKS!!!)

When the circuit is idle it is drawing about 60mA combined over both tubes. How high should that voltage go during high volume playing.

I was monitoring the bias (1 ohm R hanging of of the cathode) while playing and it was climbing upwards of 250mA (mV).

Is this normal? Talk to the rookie, please!!!

[Tom Phillips]

Sounds normal to me.
When there is signal flowing through the tube you are measuring the operating current not just the bias.
Regards,
Tom

[mikeboone]

Thanks...

I had never monitored it before and was just curious. I was having some bigtime tube failure problems and was monitoring current to hopefully see a problem before smoking another tube.

Thanks again...
mb