Metropoulos Forum

My 73 50watt head hums quite loudly on the 4 ohm setting, 120hZ sort of hum. It goes away when I move to 16 ohm setting and different input in the 1960A stereo cab I'm using.
Is the transformer going bad or is it possible something is wrong with the switching circuit in the cab?

Old thread, I know but just my .02 cents. Transformers are a lot like fuses and light bulbs. They either work or they don't. No real in between about them.