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Hey guys, I'm hoping I can get some help with an issue that has me stumped.
Stock JTM45 circuit with two 8mFd bias caps in parallel, 15k resistor between them, 56k to ground.
All of a sudden, the tubes are drawing very little bias current, 5mA per side. When I installed them, they biased at 38mA, negative bias voltage -36V.
Tried different sets of tubes, they all draw the same, low current.
Bias voltage is still -36V.
Changing the bias set resistor (the 56k to ground) shows almost no effect. Values from 15k to 100k only result in app. 2mA difference of bias current.
Changed out the bias caps and diode, to no avail. Caps are grounded properly.
What might be going on here?
Thanks, Hugo
Stock JTM45 circuit with two 8mFd bias caps in parallel, 15k resistor between them, 56k to ground.
All of a sudden, the tubes are drawing very little bias current, 5mA per side. When I installed them, they biased at 38mA, negative bias voltage -36V.
Tried different sets of tubes, they all draw the same, low current.
Bias voltage is still -36V.
Changing the bias set resistor (the 56k to ground) shows almost no effect. Values from 15k to 100k only result in app. 2mA difference of bias current.
Changed out the bias caps and diode, to no avail. Caps are grounded properly.
What might be going on here?
Thanks, Hugo
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