Fender Bassman in the drip edge fashion, with the metal grill going around the silver grill cloth. From around the 32nd week of 1967.
One of the power tubes had fallen out of the socket and was re-inserted in the wrong orientation (center pin to line up the tube was broken off). It also was really noisey on channel 1 because the V1 grid wire was right next to the heater wire. Moving it over 2″ removed the hum.
I see so many old Fenders with extremely loose power tube sockets. I think this is because the tubes get jostled around for decades when people shove the AC cord in and out of the headcase. Most can be re-tensioned, some have to be replaced.
Fender Bassman AB165 schematic