This video features the rather extensive repair of a very unusual 1965 Fender Bassman with features specific to both AA-165 and AB-165 circuits, including several "unfinished" circuit characteristics. The initial issue was a completely fried 6.3VAC center-tap, but during its evaluation and repair, other unusual circuit peculiarities were discovered. Join us as we explore and repair this unique circuit.

Additional topics include alteration of the NFB circuit and use of the Polarity Switch to make it switchable, discussion of hum cancellation in 6.3VAC filament wiring, repair of my damaged Eurotubes bias probes, and modification of the Bass Channel tone stack to improve tone and favor guitar use for the customer.

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Additional NOTES: 1.) The midrange tone control idea was deemed unnecessary. 2.) The audio demo was done with single-coil pickups (as Leo intended), NFB "off", and Tone Controls at neutral (5) position. 3.) The fact that the modified 6.3VAC circuit withstood hours of circuit and audio testing justifies, IMO, retention of the original power transformer.