Bassman line out?

[bnwitt]

Setup you ohm meter for low range or if autoranging just measure the resistance between the three primary leads. Assume the red is the center tap to start with. If you check from the red to the black and then from the red to the brown you should get readings that are close. Let's say you get 90 ohms from red to brown and 96 ohms from red to black. You'll then get 184 ohms from black to brown. That is how you find the center tap. The wire that has fairly equal resitance to the other two is the center tap and goes to the B+ connection. The other two wires go to the pin 3 on the power tubes. If you amp uses negative feedback besure to leave the wires long enough to switch them on the power tubes in the event you get squeal at start up.

If this test doesn't work with the black wire, find out which two wires have low ohm readings to the red wire. Those will be your secondary plate wires. There should not be low resistance between any secondary wire to any primary wire.

[Chuck H]

how would i know if they are backwards?

On most of the "Fender" transformers I've hoohed up (probably all, but I can't remember) the blue (black?) lead needed to be on the power tube plate that had it's grid fed by the preamp input side of the PI. If it is backwards your amp will squeal and be unstable. So as suggested, leave the OT primary leads just long enough that you can swap them if needed.

Chuck