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Old 8th January 2013, 03:42 PM   #1
mskl99 is offline mskl99  United States
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Default Grounding considerations with external PS

I am building an external power supply for an EL34 push-pull ultralinear amplifier. It will be rectified with SS. I have been unable to find out anything about grounding.
Are there any special grounding considerations? Should I run a heavy wire to connect the 2 chassis. Should I run a separate wire to connect the power supply star ground to my amplifier star ground?
I think I'll use DC for the heaters to make things easier.
Thanks for your help.
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Old 8th January 2013, 04:16 PM   #2
Merlinb is offline Merlinb  United Kingdom
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The power supply chassis should be connected to mains earth via a short wire from the IEC inlet.
But the power supply circuit-ground itself does not need to be connected to the chassis, although it might be a good idea to connect it to chassis with a 100nF 1kV ceramic cap, say, to keep RF ground impedance low.

The amplifier chassis does not require any explicit connection to mains earth, since no mains wires enter this chassis. However, you will presumably want to connect the amplifier chassis to audio ground at the audio input connector, for shielding reasons.

Circuit ground should then be laid out in the usual way (star, bus, whatever you prefer). The power supply ground simply connects to the amplifier ground via the umbilical cable.

Last edited by Merlinb; 8th January 2013 at 04:23 PM.
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Old 8th January 2013, 04:34 PM   #3
mskl99 is offline mskl99  United States
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Wow, thanks, it's great to get my question answered from an unimpeachable source. I plan to use the regulator circuit from your book, p. 204.
If I decide to heat the EL34 filaments with AC, is there a problem running twisted 6.3V AC wires with the 380V Vb wire.? I'll probably put in another smoothing RC stage or two on the amplifier side.
Thanks again. Your book is terrific.
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Old 8th January 2013, 04:43 PM   #4
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally Posted by mskl99 View Post
If I decide to heat the EL34 filaments with AC, is there a problem running twisted 6.3V AC wires with the 380V Vb wire
No, I wouldn't worry about crosstalk from the heater to the V+. What little noise does couple across should be filtered out quite effectively by the smoothing caps in the amp.

Not sure about unimpeachable...
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