Amp circuit ID

[redhawkblues]

Vintage Super Reverb... is it an AB673 or an AB568 circuit? Can’t figure out to post a pic from my phone...

[Steve25]

AB763 is the first amp schematic, this designation means August of 1963 when Leo Fender still owned the company, as in pre CBS.
AB568 is the May of 1968 schematic revision of this amp when it was owned by CBS and several changes had been made internally to the amp circuit.

All Fender SR amps have one big flaw in the power suppply section which makes for unneeded hum, that being the ground for the output tube screen section is landed with the preamp filter grounds when it should be landed with grounds off of the power transformer.

To change this you will need to run a new separate ground wire.