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Gluca 14th March 2005 06:51 PM

Parafeeding a push pull
Mumble mumble ... I searched the forums but I didn't find any post on parafed push-pull stage.

Probably I am missing the point but I think that leaving the dc supply out of the tranny can be welcome also in a push-pull. The tubes can be loaded by a (large choke) and capacitor coupled to the OPT.

Any comment or reference to look at? :confused:


analog_sa 14th March 2005 07:08 PM


I think that leaving the dc supply out of the tranny can be welcome also in a push-pull.

Why? It will only help dealing with the dc flux due to tube imbalance. A high price to pay for this. I use airgapped PP transformers and this seems a simple solution for a lazy a*s*s

Eli Duttman 15th March 2005 01:23 AM

I suggested parafeed in a PP amp in the following thread.

My concern wasn't magnetic flux. Old low voltage "iron" had been salvaged from SS equip. I suggested parafeed as a way to protect the insulation in the trafos from the B+ rail.

Gluca 15th March 2005 12:06 PM

Well tube balancing is one aspect. I was considering that a parafed PP trans can be winded with smaller gauge wires, as no DC current will flow, giving smaller dimensions.

The real question should be: can this improve the THD and freq/time response as the leakage inductance and stray capacitance can be made smaller? Probably it would be a negligible effect and, that's an adverse effect, you are adding a capacitor in the signal path.

Actually the question came out while considering the possibility of using an old SE trans for a PP stage.


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