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 ~ 😀 😀 😀
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 ~ 😀 😀 😀
If the amp is wired to use NFB, it will oscillate if connected backwards. If it does, then turn it off and switch it around.
Nope... no concerns...
Tim
Nope... no concerns...
Tim
thank you so much Sch3mat1c 😀
one more silly follow-up question: how do I determine if the amp oscillate? (say I have a dummy 8 ohm/200W resistor load, a oscilloscope)
one more silly follow-up question: how do I determine if the amp oscillate? (say I have a dummy 8 ohm/200W resistor load, a oscilloscope)
Well,if Instead of seeing the amplified input signal (or nothing,with no input signal-except perhaps a bit of hum.) You see a bunch of HF trash all over the scope's screen- you'll know.
I had this happen to me once,and the output tubes arced over internaly (but they still worked afterwards.)
Either way,you'll quickly figure it out. 🙂
I had this happen to me once,and the output tubes arced over internaly (but they still worked afterwards.)
Either way,you'll quickly figure it out. 🙂
thanks for the valuable info.!
WOW, I'd better try some ready-to-die or cheap tubes to be the tester, defintely not the NOS U.S. / Euro tubes!
DigitalJunkie said:
WOW, I'd better try some ready-to-die or cheap tubes to be the tester, defintely not the NOS U.S. / Euro tubes!
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)?
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
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.
enochRoot said:
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.
Why not run a sine wave into the secondary and monitor with channel A on the 'scope. Using channel B you will very quickly find out where the top of winding is (phase) on the primary. No smoke, no muss, no fuss.
-Chris
-Chris
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