To add a 1.5 volt winding first remove the transformer shell. Transformers are usually held together with 4 screws. Most have a little room between the metal core and winding. You will need to add a few turns of wire between the original winding and core. It doesn't take very many, try 5 turns and see what you read. Use 16 GA wire for a 1.5 volt winding. Add enough wire so you measure around 2 volts without a load. This will drop down with tubes and radio wiring.

Your secondary winding should be higher than 100-0-100, maybe 250-0-250? There will be voltage dropped across the B+ filter network and your 71A's need around 150 volts on the plate.

Norm

:Hello All,
: I am working on an American Bosch 28AC that needs a new power transformer. Its windings are B+, 2.5, 5.0, 5.0 and 1.5.
: Someone told me, I believe it was Norm Leal, and I have heard before, that I can add a 1.5 volt winding to a power transformer. Can anyone suggest a transfromer I can use. All I can find are sealed and don't have the space between the windings and the laminates to do that. Would this be wound on a filament transformer or the power transformer or does it make any difference? What voltage should the B+ winding be 100-0-100?
: Please help.
:
:Thanks,
:
:Dave...