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#1 2008-04-27 04:17:39

Diablo
Member
Registered: 2007-12-01
Posts: 139

Troubleshooting help needed

Not satisfied to leave well enough alone, I opened up my V4 again to check the bias voltage. I was happy to measure it at -62.5 volts. Close to the -62V listed on the schematic. The problem I found is that Pin 3 and Pin 4 of the 7027A power tubes only measure 492V. I traced back to point A on the circuit board and it also measures 492V. I checked the voltage coming into the amp at 124V. The odd thing is that before I recapped my amp, I checked the voltage at Pin 3 and Pin4 on the power tubes and measured 537V - close to the 540V on the schematic. Anyone have a clue where the voltage went or how to trace down the likely problem?

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#2 2008-04-27 06:15:14

Diablo
Member
Registered: 2007-12-01
Posts: 139

Re: Troubleshooting help needed

I figured this out with chopsticks. I had a loud hum when I opened the amp up to measure voltage. I still had the loud hum when I closed up the amp. So I went back in and started moving wires around with chopsticks. I found the hum went away when I moved the wire connecting the two power supply filter caps in series. A likely poor solder job. Twisted the wire so there was no hum and measured the voltage....it was back to 545V. Eureka.

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