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The plot thickens.....
Put in a good 560 ohm resistor (in B+ line) and the HV supply works fine.
For about 4 minutes, then the 25L6 current starts drifting up until the
osc shuts down. Get the same symptoms with a 125 ohm resistor
in B+ line. The grid voltage is running low (approx -60v instead
of the proper range of -100 to -150v. Tried re-positioning the
1B3 feedback spring, and a different 1B3. No improvement. The
150K grid resistor reads 170K, so didn't think it was off enough to
cause this, but will replace next. Also have replaced all caps in
the circuit with new (and checked) units. The 25L6 tests good but
have tried another one with same results.
Steve
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