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Title: Overtone power supply voltages Post by: Cinstan on August 14, 2008, 04:12:50 PM Hi guys-
Long-time lurker, first-time poster. Just put my Overtone together and have some issues. Does anybody know what the various power supply voltages should be? I have only 330 V or so on the 6L6 plates and 125 on v1 plates. This is accompanied by an oscillation in the output signal, I checked the OT primary polarity since it has been noted on this forum and the oscillation seems to be worse when I reverse the wires. Any thoughts would be greatly appreciated. ??? Update-with no power tubes installed, B+ voltages are 420 or so, preamp works as expected, clean, no oscillation or hum in the preamp out signal. Inserting the output tubes (biased as OFF as possible) drops the plate B+ to 330 or so and there is significant modulated power supply hum in the output transformer signal. I have checked and rechecked all the connections, tried a couple of sets of 6L6s too... Title: Re: Overtone power supply voltages (problem solved) Post by: Cinstan on August 16, 2008, 07:23:32 PM Got the amp working. Turned out that the two main filter caps (200UF 300v) were open. I had jumped them individually with a known good cap but since they are in series I didn't catch on right away. Jumping both brought the B+ right up to where it should be and eliminated the hum in the output.
Pic shows the test cap in place-amp runs fine this way but I will replace the caps with two of the original value. What are the odds of both brand new caps being bad?, go figure. I even took the time to form them using the variac before powering up the amp for the first time. Anyway, now on to the fun part...playing and tweaking ;D |