Strange hum problem caused by reversed PT primaries?

[JayB]

 I couldn't figure out where the hum was coming from. Sounded like 60hz coming through. Looked at everything I could think of. It was pretty bad too. The louder you turned the master, the worse it got. I bypassed the preamp into another power amp, bypassed the preamp and played straight into the power amp. Nothing I did changed it. Finally I looked at the primaries and they we're reversed with the fuse on the return line. I switched them around it's gone? I never encountered that before.

[HotBluePlates]

Is there a hum balance cap/ground switch still on the primary side?

Is there any chance that the act of reversing the primaries corrected some other fault? Something like a cold solder joint, poor mechanical connection, excess solder flux, etc?

I can't see how swapping primary leads could make a difference, except in light of a hum balance cap or a different fault.

[RicharD]

Seems very odd.  I'm inclined to agree with HBP that there might be another problem.  Grasping at straws, there might be a primary to shield short inside the PT, in which case you need to look at your wall receptacle grounding too because there shoulda been sparks, a tripped breaker, or earth shattering kaboom.  Is it a funky PT with a million leads?  Perhaps a hi resolution picture is in order?

-Richard

[JayB]

I have no idea. I can't recreate the problem even after I switched the primaries and it doesn't do it. Checked the wall socket just in case and that's fine.

Just an ordinary fender PT.