Wire colors JMP 50 OT?

[Doug]

Can't find info on the color codes.

I have a 1976 Marshall JMP 50 that has been hard wired to 8 ohm output with other wires snipped. I believe the 8 ohm wire is green, the snipped wires are yellow and gray. Yellow 4 ohm? Gray 16? A purple wire was soldered to the 8 ohm tap directly to the speaker jack. Purple the "common" that should be wired to the center of the impedance switch?
Thanks
Doug

[drewl]

Don't have the book with me, but I think purple is the feedback tap, it should go back to the pc board to the phase inverter.
You will measure slight differences with an ohmmeter, 16ohm will be the highest resistance, than 8, and 4 will be the lowest.

[HTH]

50w Marshall OT color codes:

* grey, 16ohm
* green, 8ohm
* yellow, 4ohm
* orange, common

The purple wire from the board is the feedback wire - if your amp has a 47k feedback resistor, it would have gone to the 8ohm tap originally. If it has a 100k feedback resistor, it'll have gone to the 4ohm tap.

HTH