help needed with tube voltage power supply


2008-08-01 5:13 pm
hi there,
i've got a problem with an amp here that i can't figure out how to fix..

i've changed every single part (except the NJM2068, which i replaced with other opamps like the TL072 or 4558D), and i can't get the problem to disappear.

the problem is hum on the 220VDC output.. which is very audible through the tubes it feeds.

the whole circuit starts to oscillate.
-15VDC is stable, 10UF is also new..

the circuit did work for 15 years and i thought the 10UF or the opamp would do the job, but no.. anybody have any ideas?


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2008-08-01 5:13 pm
sorry, i forgot to check this mail account! thanks for the question!
the input is from the transformer, not directly from the wall.

i built a conventional power supply with a 3k9 Resistor after the 10UF and a second cap 33UF, but taking the ground from the power supply i get a ground loop hum. not nearly as bad as the hum from the voltage regulator, but audible.