Philisvexed

Thanks guys, some new areas to investigate. Had some experience in my youth with charged caps 😵

Evening all, Running Hartke 3500 into Hartke 115XL. Getting a terrible hum from the amp, I've read many suggestions & I think I've proved them all out. The hum occurs even with no guitar plugged in. Literally power to amp, lead to cab. I've tried different leads, different sockets (out of amp) , different jack socket into cab, different kettle leads, scuffed up the earth mount. No idea! Can anyone suggest another avenue to try? Thanks