klem kedidelhopper wrote:

So then assuming the UUT is in fact an unknown 70V transformer, I
might have the supply cranked up to almost 100V before I see this
increase in current? Can I feed this transformer off my bench variac?
Will this current increase be a sudden or very gradual increase? Lenny


Yes, if you are careful but you need a current limiting resistor in
series to protect the transformer. They are not designed to be
impedance protected. It's still not an ideal test, because the 25 or 70
volts is nominal, not an absolute upper limit. That's why I use the 1
volt to the secondary method. Then square the voltages you read on each
primary tap and multiply by the speaker impedance to get the impedance
for that tap. It only takes a minute or so per transformer, and is less
likely to kill you if you're careless.