Got this info from Fat Jimmy himself! he builds amazing amps many times using NOS parts! I plan to buy a blond Twin (1961) from him this fall! My #1 favorite Fender amp of all time!
"Bob is playing a custom amplifier I built for him based off of the old VOX style circuits. It is actually a stereo rig with a stereo preamp and stereo power amp, L & R indivisual partallel circuits throughout! Controls = (Pre) bright/brighter sw, Vol, Treb, Bass, (Power) Master, Chime, Jimmy (w/ in/out switch)"