• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

how to determine P1 from P2 of a Push-pull transformer?

hi all, I recently acquired a vintage push-pull transformer (without label of course), but I don't know how to determine primary P1 from P2...
some threads I've read long ago indicates that P1 & P2 must not be connected reversedly, or the amp might oscillate. (is that true?)
all I know so far is how to measure the primary impendence given a known secondary load... and I found out although P1 & P2 would give almost the same voltage if I input some volt into the secondary, the DC ohm of P1 / P2 appear to be quite different! (something like 100ohm V.S. 115 ohm)

as title, if anyone knows how to determine P1 / P2, please let me know :) thanks a lot ~ :D :D :D
 
ok...i'm lost

i don't get it. i thought that P1 and P2 were completely arbitrary and symmetrical. where does it matter? ie: i am getting ready to build a push-pull triode amp (no NFB), using an interstage transformer for phase splitting. as far as i can see, it looks the same no matter which plate is "on top". does this only apply to certain varieties (pentode, w/ feedback, using tubes as phase splitter, etc)?
 
Re: ok...i'm lost

enochRoot said:
i don't get it. i thought that P1 and P2 were completely arbitrary and symmetrical. where does it matter? ie: i am getting ready to build a push-pull triode amp (no NFB), using an interstage transformer for phase splitting. as far as i can see, it looks the same no matter which plate is "on top". does this only apply to certain varieties (pentode, w/ feedback, using tubes as phase splitter, etc)?

hi enochRoot, that's because with NFB, your amp is feeding back signal to the previous stage (usually the input stage). If P1 / P2 are rversed, that means you are feeding the opposite phase back. In short, the output phase and the to-be-inputted phase must NOT be the same. (otherwise it's not negative feedback then)

Alternatively, instead of exchanging P1 / P2 if oscillated, exchanging the secondary works as well. (by switching ground / speaker load, and also the NFB connection, the output phase now is reversed again) This method seems awkward and silly in practice compared to the previous one, but it is another example to illustrate how NFB/phase work in brief. :smash: