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I was having problems with a 70's Orange OR120 burning up the 1K screen resistors (melting solder and wiring, burning the ink stamp off the resistors). The OT was a replacement, and looked to be the size of a 50 watt transformer. The secondaries were wired Grey/Common, Orange/16Ohm, Yellow/8Ohm, Green to negative feedback circuit. I installed a Mercury OR120 replacement tranny and all is well with the amp now. I took off the end bells from the 50 watt tranny....see pics below. I found a Marstran JMP50/Marstran JMP139 wiring diagram with the same wire coloring as this 50 watt tranny: Wiring Diagrams. Does anyone recognize this transformer...OT50M? And would mis-wiring it into the OR120 the way I found it cause the screen resistor issue the owner was having? Thanks for your help!
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