In Reply to: RE: enough current to bias 2 x kt150 tubes posted by DAK on January 12, 2017 at 17:08:46:
A faulty diode (it may become 'open circuit' or a sort of non linear resistance) in the full wave rectifier of the bias supply might turn it into a half wave rectifier.
As a consequence DC current arises that might overheat the bias transformer.
If KT90 tubes are brand new I would also put a temporary cathode resistor durung the initial 200-300 hours ageing (to be eventually removed later on).
During the initial burn in some excess air molecules may be trapped inside the tube, excessive grid current results and getter action takes a significant time to clean up them.
"In bocca al lupo!"
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Follow Ups
- RE: enough current to bias 2 x kt150 tubes - 6AS7_6SN7 23:10:22 01/12/17 (1)
- RE: enough current to bias 2 x kt150 tubes - DAK 09:56:50 01/13/17 (0)