Identifying the common lead in output stage of a Xfmr

[kanasmask]

Hi there, I am seeking assistance in identifying which output lead of an audio output transformer should be grounded (the common lead), and which one (the hot or the positive lead) should be connected to the positive speaker out socket . The one under consideration is an ultralinear one: P3591A. Many thanks

 

[PRR]

Hook it up, either way, with a dummy load and meter.

If the "Negative" Feedback is actually positive, it will quickly HOWL at full power.

Reverse the leads. If now it is stable (no output), that's right.

 

[Alllensoncanon]

And if you must know the answer before the amp is built and you don't have a scope, you can apply an "AC" signal to the primary windings. Assign one of the primary winding terminal as a "dot". Connect one end of the secondary (speaker) to the non-dot terminal. Put an AC volt meter between the "dot" primary terminal and the remaining free secondary terminal. Note the voltage. Reverse the secondary wires/terminals and measure the voltage again. Note the one that has an slightly higher voltage reading. On that one, the free secondary wire is the "Common" and could be a ground reference for an non-inverted signal for NFB purpose.

 

[grovergardner]

On my Partirdge WWFB the "positive" leads were to the right, where the 15 ohm label is. And the yellow lead soldered there would be typical for a 16 ohm lead.

 

[kanasmask]

Hi, I am much obliged for the advices you put forth. Will go ahead accordingly. I have a set of signal generator and a scope to work with. I hope I can conceptualise the experience and gain more knowledge. Will revert soon. Thank you.