Got this amp to fix :
Despite it has not the typical “Alu frame drip edge”(removed by a previous owner ?), I think it’s a “blackline” from end 67 or beginning 68 : transformer code, AB763 schematic, blackline, chassis stamp (A324xx) …
First : remove the Death Cap. Very dangerous, because in case of capacitor failure, the hot side of the power lead becomes directly connected to the chassis. And here it is : this capacitor WAS a short circuit !
Interesting diagram from http://www.unclespot.com/3prongconversion.JPG (thanks to him !) :
Anyway, this amp is a kind of blackface in disguise !
So … tube tested with my Hickok 600A, rebiased, vibrato tested … all is right … except that somedays I think I will replace PSU electrolytic capacitors that are 45 years old
See recap with vintage look maintained here