BF Princton Reverb PT Question

[mikeboone]

I just recently repaired this amp and found that the heater windings (green wires) were shorted to ground causing the fuse to blow. The PT part number is 022772.

I had a replacement PT in my stash from my 5e3 days that worked nicely and all is well...

Question: On the original PT there is a wire (black/white stripe) that was grounded with the CT (green/yellow) that is shorted to the heater wires. The CT is not shorted to either.

Does anyone know what that black/white wire is for? Can the PT be used without it?

Thanks,
Mike

[techineer]

Have you tried using an ohmmeter to see which other wires/windings it is connected to?

None of the diagrams that I have for the Princeton Reverb show a black/white wire (if they give any colors at all). It would help to know which winding it is a part of.

[melvin]

The heater wires are always pretty close to being shorted to ground due to the fact that the heater coil has a center tap, grounded to the chassis. This is most likely what your black/white wire is. I'm not sure I would use a 5E3 power transformer for this amp, if that's what you mean to do. The Princeton Reverb has more tubes and therefore more current draw from the heater winding than a tweed deluxe, which could cause it to burn up.

If you don't have a center tap for a heater (filament) winding on a new PT, you can make a virtual center tap by connecting 100 ohm resistors (1/2 watt) from each side of the filament supply to ground. This is usually easiest to do at the lamp socket.