Quote:
Originally Posted by John10b
... Do you have any views on the high cathode voltage?
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EL84s, and so I suppose UL84s too, can be very prone to going gassy which leads to the control grid voltage rising and the cathode current going high as a consequence. I see that the OP says in the first post that the grid is at 0V. The question then becomes 'How close to 0V ?'. Even a volt or two positive can make a significant difference to the cathode current in this relatively high transconductance valve.
Cheers,
GJ