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Question for Stax amp DIY types

post #1 of 3
Thread Starter 

I got a pair of old Stancor push pull opt.  They list 10K center tapped input to 15/8/4/500 ohm output windings.

 

I have a question about what is possible to construct.  I have a 300b amp that I use for headphones with a Stax transformer adaptor.  

 

The output impedance of 300b tube is about 700 at the plate.  My amp has a B+ of about 300 volts.

 

Question is, could I use the push pull OPT in REVERSE, using the 500 ohm end as an input attached to the B+ and the 300b output tube, then wire the 10K output push pull to the stax outputs directly without a second transformer?

 

  I estimate the voltage multiplier would be about 4.4 wiring it this way, but would create the B+ of 300 on the 500 winding. The center taps of the 10K ohm push pull end would be attached to the Stax bias board as usual, with the signal wires attached directly to the stax headphone socket from the Stancor transformer.

 

  This would allow just one transformer between the 300b instead of the usual two transformers for tube amp i.e. step down transformer to 8 ohm which is then routed normally to second Stax transformer box for voltage step up.

 

Don't know if it is do-able or not, seems like it should work.  Or will it result in a mushroom cloud and pieces all over the room?

post #2 of 3

The 300B's need more primary impedance to be happy and the high ratio will cause all sorts of trouble.  Ideally you shouldn't run a an amp like that at much more than 1:2 ratio but 1:4.5 is rather high.   This would make for a nice transformer for a Stax trafo box though but I would stick with the 15 ohm taps. 

post #3 of 3
Thread Starter 

Yup, think I will just make another upgraded, breadboard trafo box from an old SRD 5 for the time being and ponder the other questions later. 

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