bootstrapping two SE transformers into a pp one?

[Rockmonton]

i konw you can bootstrap them together, but is there a special wiring to have them operate like a normal push-pull transformer? i've got a pair of old japanese el84 ones that could be very nice but i have no use for aything in in stereo..... i was thinking of deigning a monoblock to match my current one made out of an old hammond for the basement now too.... any ideas?

[fragman56]

connect them in series and use the connection as a center tap, I think. Then you have a plate to plate load of 2 times the SE transformer load.

Just guessing here, perhaps someone could offer better advice.

[benny]

spot on fragman, except P-P load will remain the same as single tranny coz turns ratio is still the same. for example, take two 2k SE trannys and put both primary and secondary in series, turns ratio will stay the same.

[Rockmonton]

cool i thought this was right but you guys confirmed it, thanks a lot! power at same bias should be the two tubes combined now right?

[rcavictim]

Originally posted by benny
spot on fragman, except P-P load will remain the same as single tranny coz turns ratio is still the same. for example, take two 2k SE trannys and put both primary and secondary in series, turns ratio will stay the same.

IMO Benny's idea will not work satisfactorily. The only chance is if the two separate secondaries are hooked up in parallel to each other and the speaker load. Even that arrangement will yield gross inefficiencies over a proper single output xfmer.

[planet10]

I know Steve Deckert uses 2 SE OPTs in his Torii and calls it push-pull...

I asked essentially the same question here:

http://www.diyaudio.com/forums/showt...5694#post55694

As i've given more thot to it, i think you probably end up with a variation of a PSE amp....

dave

[JimW]

I did this very thing. I have a pair of stereo 2a3 se amps, so as an experiment I hooked the outputs in parallel, out of phase, and then made a simple voltage divider to use one input tube as a paraphase inverter. They work very well. I think there are a couple of manufacturers who are doing this type of output configuration.

[jlsem]

As i've given more thot to it, i think you probably end up with a variation of a PSE amp....

You won't derive the benefit of true push-pull in that DC inductance in the core won't be canceled and the transformers will saturate at high current. In other words, you can bridge the windings, but not the core.

John

[jlsem]

No need to bother with a phase splitter as well.

John