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Old 18th February 2008, 08:58 AM   #1
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Default I need a negative supply rail--but how?

Hiya!

OK, I have a pile of 6N1P tubes kicking around here, and want to use them to make a bunch of op-amps for a project. All is good, based the design on the Philbick K2-W(J) with the values of all the passive elements re-sized accordingly, so it should be fine. Except...

The K2-W (and most any op-amp, I guess) needs a -300 VDC supply as well as the +300 VDC one (usual B+) one. Question is, how do a make a *negative* supply? A schematic would be most appreciated

Many thanks in advance!
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Old 18th February 2008, 09:29 AM   #2
Colt45 is offline Colt45  Serbia
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300-0-300 trafo, full wave bridge. ground the CT.

You can use tubes.. say a 5U4 for the + rail, and a pair of dampers for the (-) rail. Or silicon.. whatever. Your choice
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Old 18th February 2008, 01:35 PM   #3
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Quote:
Originally posted by Colt45
300-0-300 trafo, full wave bridge. ground the CT.

You can use tubes.. say a 5U4 for the + rail, and a pair of dampers for the (-) rail. Or silicon.. whatever. Your choice

Dave Cigna kindly showed in an old thread of mine, that using a bridge and grounding the CT is (in fact) 2X FWCT rails wired in opposing polarities.

If symmetry between the 2 rails matters, all 4 diodes should be identical. 4X UF4007s, with each diode paralleled by a 10 nF./1500 WVDC ceramic snubber cap., will get the job done. A pair of 6BY5s, each having a separate, floating, heater supply is (IMO) the way to go, should vacuum rectification be a must.
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Old 18th February 2008, 05:58 PM   #4
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Thanks guys, and sorry about the typos in my original post (oops!).

I *think* I understand what you're telling me, with the 300-0-300 transformer being the main ingredient in the design. I'll sketch it up and try it out a little later today to see if I got it right.

Cheers!
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Old 18th February 2008, 07:30 PM   #5
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Is this correct? Ignoring the sizes of everything, of course...

Cheers!
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Old 18th February 2008, 07:36 PM   #6
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Quote:
Originally posted by wally.gribbles
Is this correct? Ignoring the sizes of everything, of course...

Yep!
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