In 1968 Fender changed to the “silverface” control panel.The circuitry was altered as well: There were changes to the bias and phase inverter circuits and, most important, the output stage.
The amps Fender produced between 19 are known as “blackfaces” because of their black control panels, and their designs remained largely unchanged during this period.
But don’t lose sleep over this, as most post-blackface “improvements” can be returned to pre-’68 specs, yielding a pretty toneful amp. I hope that sheds a little light on your amp, but remember: It’s only a bad amp if you don’t like it!
Jeff Bober is one of the godfathers of the low-wattage amp revolution.
The tube is fed a signal (from channel 2, or the “vibrato” channel, in the case of Fender reverb amps).
The tube’s output connects to a transformer, exactly as in a single-ended amp like a Champ.
You can easily identify these 1968 amps by the silver-metal band around the perimeter of the grille cloth.