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Old 21st January 2012, 06:30 PM   #1
wicked1 is offline wicked1  United States
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Default PSUD modeling old amp PS fails.

I'm trying to model a PS for an old amp I've got.

333-0-333 to 6ax5rect to 40uf cap&load to 15kres/20uf cap to 20kres/10uf cap&load.

It fails, tells me it pulled the voltage below zero, and shows less than a volt on my loads. (I have delayed the measurement, and it didn't change anything)

But.. this is a working amp, and I'm entering components exactly as they are.

Now, if I change the resistors down to 150ohms for the first, and 1k for the 2nd, the model works about the way the real amp does.

Can someone enlighten me as to why? I'm modifying the amp, and want to make some changes here.

Last edited by wicked1; 21st January 2012 at 06:32 PM.
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Old 21st January 2012, 07:00 PM   #2
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Did you use a resistor or current-sink load?
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Old 21st January 2012, 07:13 PM   #3
euro21 is offline euro21  Hungary
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15000 and 20000 Ohm ???
Too much.... or (real) output current only some milliamper.

For example PSUD with 150R and 1K , output current (Load 10K) 34ma (340V).


Input voltage: 430V ( V/C1/ )
Simple voltage divider: Re: 35K (15K+20K) + Load = ..... K

Output current: Io= V/Re
Output voltage: Uo=Io*Load
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Last edited by euro21; 21st January 2012 at 07:16 PM.
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Old 21st January 2012, 07:34 PM   #4
wicked1 is offline wicked1  United States
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Yes. 15,000 and 20,000. It does sound like too much, but here's the original schematics..

-actually, that image doesn't help at all, at that size.. but here it is
http://recordist.com/ampex/schematics/620man/620-1.gif

But really, all that you probably need to know is it's a standard 6v6 pp amp.
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Old 21st January 2012, 08:24 PM   #5
euro21 is offline euro21  Hungary
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Hoppa....it is old style PSU, like Dynaco ST-70.

From C308b 350V to push-pull OPT ct (69.4mA).
R319 (15K) -and C308a 20uF- to 6V6 G2 (0.67 mA)
R318 (27K) -and C307 10uF- to phase splitter (2.6mA)
R317 (39K) - and C306 4uF- to first tube (1.54mA)
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Old 21st January 2012, 08:27 PM   #6
wicked1 is offline wicked1  United States
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OK, maybe i've got it.. I had too much current draw specified on the 2nd current tap.. I suppose that's only about 7ma. (Im not counting the screens, as they're already triode wired)

Oh, thanks a lot Euro, didn't see you had replied w/ that file.
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Old 21st January 2012, 11:23 PM   #7
wicked1 is offline wicked1  United States
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Thanks again, Euro!!

I was going off a hand drawn schematic that came w/ the amps which had an error w/ the first resistor location. (it was resistor then load, where as it's actually load then resistor, like the online schematic) Then I was also not paying attention to what I was doing w/ the 2nd current tap and had it at 100ma.
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