Characterizing mystery OTs

[BackwardsBoB]

Can I just plug a signal generator into an unplugged amp's speaker jack with the (fixed bias push-pull) power tubes pulled, measure the voltages on the plate pins and come up with a turns ratio, then multiply it by 8 Ohms and get an approximate value for the transformer's Raa?

[Steve Conner]

Yes. As long as you remember that the transformer may load down a signal generator somewhat, so you have to actually measure the generator's output voltage, not assume that it's putting out what it says on the dial.

Also, watch out for those flyback diodes that some amps have from the power tube plates to ground: with the B+ turned off they'll shunt your voltage away and it won't work.