P-P OT for SE use...

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P-P OT for SE use...

Postby ThisLifeILead on Wed May 20, 2015 5:04 pm

Howdy folks, I found something interested that has me asking questions...
I picked up an old Hammond ext speaker that has the amp built in. The OT is a potted vintage 60's hammond 1635. 5K primary for Push-pull.
The amp in questions employed a single 6V6 as the output. The primary was wired plate to plate (one fed B+ and the other went to the 6V6 plate) and the center tap was unused.
The OT is spec'd at 30W output!! so its big for a single 6V6.
Can this be done on other OT transformers? or the fact its ok is this OT is potted and massive? How does this affect primary impedance?
The reason i ask is,
i have a vintage Ace tone model 301(2x8" speakers) that needs to be reworked for a new output tube and OT. the OT is shot. I have the Filament trans ready to go and I have a a few 6v6 P-P pulled OT's just laying around. Could i wire one of these 6v6 PP OT's for a SE 6v6?
:thumbsup: :jam:
"Great spirits often encounter violent opposition from mediocre minds" - A.Einstein
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Re: P-P OT for SE use...

Postby ThisLifeILead on Tue May 26, 2015 4:17 pm

nobody has done or seen this before? :say_what:
"Great spirits often encounter violent opposition from mediocre minds" - A.Einstein
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Re: P-P OT for SE use...

Postby PeterS on Wed May 27, 2015 3:20 pm

For a given wattage etc a single ended transformer is generally bigger, but if you go up in size there's no reason not to use a P-P transformer for single-ended. The issue is that a push-pull design has the idle current running through the two halves of the primary in opposite directions, so the net magnetic field in the core is roughly zero. Then when there's a signal you get some amount of field... alternating in direction.
In a single ended design you have a field in the core at zero signal (due to the bias current for the tube), and providing a signal varies the field up and down. So the maximum field is large, since it is being varied around some starting value that isn't zero. So a transformer designed for push-pull may saturate its core when used for single ended.
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Re: P-P OT for SE use...

Postby ThisLifeILead on Mon Jun 01, 2015 2:18 pm

:thumbsup: thnx Peter :cheers:
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