Output Transformer; Push Pull to Single Ended?

searon386 · 9th August 2011, 11:07 PM

I'm trying to build a "spare parts" amp with basically just radio tubes and spare guitar amp tubes I have lying around. I have a power amp strip that I believe came out of a phono amp. It only has an output transformer which I believe is designed for push pull operation (its one of the amp strips that has two 50v heater tubes and one 10v heater tube). I was wondering, Push Pull OTs can be used as Single Ended too, correct? you just send your B+ line to one side and the plate to the other, leaving the center tap un-used? And I was also wondering if the center tap on the transformer could be used like those 40% screen taps to reduce harmonic distortion like on the expensive Hammond trannies? I figured a center tap is (i'm guessing) 50% of the primary, so the 10% would be a difference but not that big of a difference? Anyone who could help would be much appreciated. Thanks again.

tomchr · 9th August 2011, 11:13 PM

No. For SE operation, DC current runs through the transformer primary. To support the DC current without saturating the core, the core permeability needs to be lower. This is typically accomplished by putting a gap in the core.

PP transformers do not have gaped cores, hence, won't handle the DC current of a SE output stage.

The two are not interchangeable. You might be able to use the transformers in a parafeed configuration, though.

~Tom

wrenchone · 10th August 2011, 12:10 AM

It sounds like with that small of a tube complement, the transformer may be single ended after all. How many leads does it have? If only 4, it's single ended.

searon386 · 10th August 2011, 10:41 PM

Problem is I don't have the chassis with me at the moment. i'm in the middle of a move and i'm trying to find all this stuff, but the guy i got it from told me it was pushpull, although i highly doubt it as well.
What if the DC current is extremely low for the SE stage? let's say ~ 35ma? and what is a Parafeed config?

9th August 2011, 11:07 PM	#1
searon386 diyAudio Member Join Date: Jul 2011 Location: Houston, TX	Output Transformer; Push Pull to Single Ended? I'm trying to build a "spare parts" amp with basically just radio tubes and spare guitar amp tubes I have lying around. I have a power amp strip that I believe came out of a phono amp. It only has an output transformer which I believe is designed for push pull operation (its one of the amp strips that has two 50v heater tubes and one 10v heater tube). I was wondering, Push Pull OTs can be used as Single Ended too, correct? you just send your B+ line to one side and the plate to the other, leaving the center tap un-used? And I was also wondering if the center tap on the transformer could be used like those 40% screen taps to reduce harmonic distortion like on the expensive Hammond trannies? I figured a center tap is (i'm guessing) 50% of the primary, so the 10% would be a difference but not that big of a difference? Anyone who could help would be much appreciated. Thanks again. __________________ I play all my weird amps in my band, Ulfrik. You can like us on facebook if you want. http://www.facebook.com/Ulfrik

10th August 2011, 10:41 PM	#4
searon386 diyAudio Member Join Date: Jul 2011 Location: Houston, TX	Problem is I don't have the chassis with me at the moment. i'm in the middle of a move and i'm trying to find all this stuff, but the guy i got it from told me it was pushpull, although i highly doubt it as well. What if the DC current is extremely low for the SE stage? let's say ~ 35ma? and what is a Parafeed config? __________________ I play all my weird amps in my band, Ulfrik. You can like us on facebook if you want. http://www.facebook.com/Ulfrik

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9th August 2011, 11:13 PM	#2
tomchr diyAudio Member Join Date: Feb 2009 Location: Greater Seattle Area	No. For SE operation, DC current runs through the transformer primary. To support the DC current without saturating the core, the core permeability needs to be lower. This is typically accomplished by putting a gap in the core. PP transformers do not have gaped cores, hence, won't handle the DC current of a SE output stage. The two are not interchangeable. You might be able to use the transformers in a parafeed configuration, though. ~Tom

10th August 2011, 12:10 AM	#3
wrenchone diyAudio Member Join Date: Feb 2004 Location: Silicon Valley	It sounds like with that small of a tube complement, the transformer may be single ended after all. How many leads does it have? If only 4, it's single ended.

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