I just got a Sunn Conceret bass head-- red knob-- about circa 1976. Cleaned up some scratchy pots and played it for about 1/2 hour. It had more audible 60 hz hum than I remember my old (silver face) one had in the early 70's. The amp ran pretty hot with an 8 ohm load, and went into thermal shutdown after 1/2 hour of light jamming with Youtube videos. It did reset after it cooled down. I suspect it needs power supply caps. My question: could the constant 60 hz hum from the leaky caps be the cause (I think yes). Anyone else experience this with old ss lead sleds?