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Old 28th April 2013, 10:30 AM   #1
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Default Don't be stupid, you can't possibly do that with output transformers?

Can I parallel two push pull ul output trannies, each with one primary side o/c?

The idea is that both secondaries are full parallel, the primary centre taps are connected and only the working half of each primary is wired to the valves.
They are matching transformers (same make and model) pulled from old record players, that commonly blow one side of the primary.
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Old 28th April 2013, 10:37 AM   #2
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Hi!

If you only connect one half of the primary, the core will get saturated, unless you keep DC away, for example by using parafeed. But this will require a plate choke for each tube

Best regards

Thomas
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Old 28th April 2013, 12:15 PM   #3
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Thanks for that, I thought I was being hopefull.
I'll have a little read about parafeed as I don't know much about this type of setup. I doubt though that the cost of the chokes will be less than just bying a new output transformer.
Many thanks,
Adam.
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Old 28th April 2013, 12:48 PM   #4
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Quote:
Originally Posted by adamgillingham View Post
Thanks for that, I thought I was being hopefull.
I'll have a little read about parafeed as I don't know much about this type of setup. I doubt though that the cost of the chokes will be less than just bying a new output transformer.
Many thanks,
Adam.
There are other ways to load the tubes then chokes .

And there´s SEPP topology.
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Old 28th April 2013, 12:54 PM   #5
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Or with 4 tubes... which is essentially a bridged or paralleled amp like an ST-70. I did just about that once, used one channel to drive two channels of outputs...
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Old 28th April 2013, 11:04 PM   #6
AJT is offline AJT  Philippines
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when paralleling OPT's make sure that:

1. they are identical
2. parallel corresponding leads so that phasing is maintained
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Old 29th April 2013, 12:01 AM   #7
llwhtt is offline llwhtt  United States
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The Bogen MO-200 uses two paralleled 100 Watt OPTs to achieve it's 200 Watts.

Craig
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Old 29th April 2013, 01:11 AM   #8
godfrey is offline godfrey  South Africa
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Plan B is to be a total pervert and run DC bias current through the secondaries, to cancel the magnetizing effect of the DC current through the primaries.

That would work best if the output tubes are arranged as a LTP, fed by a constant current source.

edit: E.g. The secondaries could be wired up like this:
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Last edited by godfrey; 29th April 2013 at 01:22 AM.
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Old 29th April 2013, 02:01 AM   #9
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Quote:
Originally Posted by godfrey View Post
Plan B is to be a total pervert and run DC bias current through the secondaries, to cancel the magnetizing effect of the DC current through the primaries.

That would work best if the output tubes are arranged as a LTP, fed by a constant current source.

edit: E.g. The secondaries could be wired up like this:
Like this ?

Will this circuit work ?
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Old 29th April 2013, 02:14 AM   #10
godfrey is offline godfrey  South Africa
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Yes, that kind of output stage.

Last edited by godfrey; 29th April 2013 at 02:34 AM.
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