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Old 13th July 2007, 03:33 PM   #1
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Default Power supply filter mod

I have a 330-0-330 volt power transformer, solid state rectified into a CRC filter. C1 = 220 uF, R = 47 ohm, C2 = 440 uF. B+ for stereo push-pull EL84 tubes (four tubes total) is taken off C2. I'm seeing about 390 volts here, which might be more than I would like. The EL84 are cathode biased, so they aren't seeing all of that across them, but it still seems like a lot to me. I've got them biased between 31~33 mA to keep overall dissipation down.

I'm considering replacing the R with a 150~200 ohm, 15 watt cemented resistor. I expect this will burn an extra 15~23 volts, bringing the B+ down into my comfort zone. It has been warned (by more than one) that I might hurt the amp's ability to respond to transients by increasing this resistor. Any thoughts?

Should I just leave it alone? The tubes don't seem distressed. I have nothing else to compare, but it seems like it sounds pretty good the way it is now.
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Old 13th July 2007, 03:43 PM   #2
Tweeker is offline Tweeker  United States
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One way to drop voltage without effecting regulation would be to put a zener on the center tap.
Be sure your foil hat has a good low impedance ground.
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Old 20th July 2007, 09:31 PM   #3
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Go to a choke input filter.
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Old 21st July 2007, 01:50 AM   #4
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I thought about it. It'll drop the voltage to around 280V. I was hoping for something nearer 360V or so.
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