The circuit, though, is the real giveaway; the presence of any original blue Mallory coupling caps will warm the heart of any fan of vintage Fenders, but those two enormous .25-u F caps in the Bass Instrument channel (to the left of the board) are real rarities, found only in the 6G6, 6G6-A, and 6G6-B amps.
So, if Fender was tip-toeing toward a new cosmetic style in the black control panel and knobs on this one, it was still loading in that rather quirky, short-lived 6G6-B – and producing an amp that would become a secret weapon of several in-the-know guitarists as a result.
While the Normal channel on these amps is very much the preamp design that would become famous in the blackface amps, with the tone stack sandwiched between the first gain stage and a second gain make-up stage, the Bass Instrument is a real oddity.
This channel opens with a cathode-follower that feeds the tone stack – well, the Bass control, at least – though one that’s somewhat different from the cathode-follower familiar from larger tweed amps (yes, other than in the fact that it comes before, rather than after, the primary gain stage).
Some, though, will reach for the cherished (and much more accessible) 50-watt head into which that combo evolved in the ’60s – a concerted effort by Fender to re-think the template and create a viable bass amplifier…
one that resulted in yet another outstanding tone machine for guitar.
Compared to the AA864 Bassman that would follow in ’64, and the AA165 introduced shortly thereafter, the 6G6-B still used a 7025 (a rugged 12AX7 type) in the phase inverter, rather than the lower-gain 12AT7, and also had the Presence control within the negative-feedback loop, to dial in a little more high-end zing at the output stage.
At some point you need to settle on a compromise where the amp sounds good, as opposed to having your controls at some arbitrary midpoint setting.
The bottom line is to make the amp sound the way you want, not where the controls must be set to accomplish this.
Mike Bloomfield favored a blond Bassman later in his career (the album , recorded in 1976 and ’77, shows him plugged into one on the cover) and Pete Townshend used one early on with The Who.
The most notable proponent of these amps today is probably Brian Setzer, who rocks a pair of them live.