Power supply filter mod

Ty_Bower · 13th July 2007, 03:33 PM

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.

Tweeker · 13th July 2007, 03:43 PM

One way to drop voltage without effecting regulation would be to put a zener on the center tap.

valveluver · 20th July 2007, 09:31 PM

Go to a choke input filter.

Ty_Bower · 21st July 2007, 01:50 AM

I thought about it. It'll drop the voltage to around 280V. I was hoping for something nearer 360V or so.

13th July 2007, 03:33 PM	#1
Ty_Bower diyAudio Member Join Date: Mar 2007 Location: Newark, DE	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.

13th July 2007, 03:43 PM	#2
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	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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20th July 2007, 09:31 PM	#3
valveluver diyAudio Member Join Date: Mar 2003 Location: florida	Go to a choke input filter.

21st July 2007, 01:50 AM	#4
Ty_Bower diyAudio Member Join Date: Mar 2007 Location: Newark, DE	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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