goldminer,I completely agree with B/MAN.TWO of the leads must be cross-wired to the volume control, and one of them goes to ground, probably the
wiper of the volume control.What this would do is effectively short out the pre-amplifier stage and cause it to draw excessive current leading to failure.
Simply put, the volume control resistor drains current for the emitter or collector of the transistor circuit. The wiper of the volume control merely taps off
some of this voltage/current, but NEVERchanges the current drain to the amplifier transistor to any noticeable degree. If the ground lead is wired to the wiper erroneously, then any rotation of the grounded wiper would be the same as shorting out the transistor.You probably need a new RX-18 board, but find out from a known good unit the proper color coding before wiring it in. Best of luck in your quest,goldminer.

Charlie</p>