Friday, March 7, 2025

TRANSFORMER: A&R 2504 output transformer

Rewired the one of the secondaries on this A&R 2504 output transformer from this Steanes Sound System S311 PA head for an 8 ohm speaker.  

This is very much a note to self for future reference:  approximately zero other people will be interested in this. 

Two bifilar winds in parallel were used for negative feedback.   Wiring them in series increased the impedance to ~8 ohms.   Not my genius idea unfortunately - full credit to Tim Robbins and the work he has published on converting Australia valve PA amps.     

Normally the secondaries are as follows

FB
FB (just under 2ohms)
0
125
250
500

6K P-P, 25w
Paired with EL34 

I’ll tidy up the wires later.   Had some other stuff to do - cyclone on the way….   



2 comments:

  1. take care, thinking of you guys ,greetings from south africa

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    Replies
    1. Thanks - it turned out OK where I live. Not so great for people in other areas.

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