hkyle, I am electrician. I am not 100 % expert on transformers. I do know
the basics. I need to know couple of things to help you.
Did you have Transformer with 12 turns Secondary?
and did you just take off the 12 t and put on 15 t.??
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Normally you need enough turns to get a decent magnetising coupling.
12 or 15 turns is not many turns.!
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Transformers are simply a ratio..... Say 600 Turns Primary : 75 t on secondary.
Thats 8 : 1 ....... So 120 V Primary : 15 V secondary....
The current will also follow this ratio - however the wire needs to be able to
handle it as well.
1 Amp Primary : 8 Amps secondary..... Oh yes its inverted , so that the
same power in ( 120 x 1 = 15 x 8 ...... the input and output power are both 120 Watts. )
All very simple.
The most common problem with Tx not working is break in wire. You can
check with multimeter - should be certain resistance from 1 to 10 Ohms
or something........
But yours may not have enough turns to get magnetic coupling, I just
dont know your TX.