There are several revered classics amid the ever-evolving circuits in the amplifier known as the Bassman, but one of the best-sounding might be a brief iteration that few have realized they were playing through. Make it one of the last of Fender’s brown-Tolex amps, and it’s all the more interesting.

Several times in these pages, we have discussed the way Fender plowed through circuit changes in most of its amps, introducing modifications at breakneck speed in the name of “perfecting” tone and performance. The practice led to some fun for the true train spotters, namely in the discovery of transitional circuits barely acknowledged in the wild.

One such rarity was presented recently by musician and Fender amp collector Tommie James, who had an inkling that his brown 1964 Bassman head was not only different, but special.

“The 6G6-C Fender Bassman is one of the best 50-watt guitar amps ever made by anyone!” James says. The amp featured here is the sixth 6G6-C he has owned and restored, though he only became aware of its true status through a fortuitous bit of happenstance, which led to the further realization that many players who rave about their 6G6-B Bassman (VG, March ’12) might actually be playing a 6G6-C.

“In 2010, I purchased a different ’64 Bassman and took it to Michael Clark for servicing,” James tells us. “He found differences in the circuit versus his 6G6-B schematic. I sent him a copy of the original that accompanied the amp, and it was for a 6G6-C, but the tube chart had ‘6G6-B’ printed on it. Michael and his apprentice at the time, Steve Hunter, said the changes in the Bass Instrument channel (Channel 1) on the 6G6-C sounded especially good.”

Like that earlier 6G6-C, this one also carries a “B” tube chart.

As with other transitional models of the late ’50s and early ’60s, it might be that Fender never printed any 6G6-C tube charts and merely used existing 6G6-B charts (if you’ve got one with a B chart, please drop us a line!), though a correct schematic was essential to proper maintenance and repair of the amp (and would have been drawn up at the factory for use in manufacturing). The more-obvious changes from B to C as found in any comparison of the two include interesting tweaks to the Bass channel’s tone stage, which is already an unusual and surprisingly complex circuit. Less obvious, though, is another fundamental change that Hunter, now working out of his own shop in Athens, Georgia, feels is responsible for a big part of the 6G6-C’s sonic veracity… with guitar, at least.

“The biggest difference between the two is the power transformer,” says Hunter. “I have a ’62 6G6-B that gives a B+ of slightly over 500 volts DC. That’s why I have to use it with a Variac set for 114 volts. TJ’s was putting out about 430 volts DC plugged straight in [to the wall outlet].

“The other difference is only in the Bass channel, which nobody uses. I personally prefer the Bass channel because of how the Treble control works as a gain boost, radically! The tone stack, on paper, is ridiculous, but it sounds so good. On the C, the mid cap is .25 microfarads and grounded, rendering the midrange on 0, the slope resistor has been lowered to 220k, and the treble is fixed with a voltage-divider circuit. To compensate for the 780,000 fewer ohms in the slope resistor, Fender reduced the Bass pot from 25k to 5k and increased the mixing resistor into the phase inverter by a factor of two. The differences are so subtle that I think it’s due to the different power transformer.”

Often overlooked in players’ investigations of what makes any great guitar amp sound as it does, the voltage supplied by the power transformer and the entire power stage play an enormous role in setting gain levels, compression, and overall playing feel. Relatively speaking, and all else being equal, higher voltages applied to the output tubes will yield greater headroom and a stiffer, punchier sound and feel. It’s an ideal state for bass amplification, but many guitarists prefer a little give and a slightly earlier onset of distortion, both of which are aided by the lower plate voltages of the 6G6-C.

While most guitarists running through ’60s Bassman heads do use the Normal channel, James agrees with Hunter that there’s some magic in the odd Bass channel on the 6G6-C.

“To my ears, the Bass Instrument channel of the 6G6-C is louder, cleaner, and has a warmer tone than Bassmans that preceded and followed it,” he says. “It’s also the last Bassman with a Presence control, which makes a difference when dialing-up the exact tone you’re seeking.”

In addition to interesting and short-lived quirks of the 6G6-C, the Presence knob and control layout that accompanies it this far into an otherwise new era of Fender design present curious anomalies that apply to the ’60s Bassman range in general. The tube chart in James’ Bassman is stamped with an “NH” date code for March of ’64, by which time Fender was well into the early black-panel design. The panel on this Bassman is indeed painted black rather than the dark brown of its predecessors from earlier in the ’60s, though it’s a black-panel in name only and otherwise laid out according to earlier models. In August of ’64, the AA864 Bassman brought the model properly into the blackface era and did away with the Presence control, as well.

Beyond that, this amp’s cosmetic presentation is something of an anomaly. Keen-eyed Bassman fans will immediately notice the odd brown Tolex covering and wheat grillecloth with gold-sparkle thread, something never known to be an option on the Bassman (which otherwise transitioned seamlessly from blond to black Tolex). Sent to noted cabinet reproduction and restoration expert Gregg Hopkins of Vintage-Amp Restoration, however, this head received full marks for originality.

“I believe it to have come from the factory with the smooth-pattern brown Tolex,” Hopkins confirms. “All seams and cuts are as were done by Fender, plus it has hot-melt animal glue and shows no signs of having been re-covered. The screen in the top shows no signs of having been removed or reinstalled, and there’s one stain in the Tolex from a pine knot underneath.”

We’ll never know whether this was all the result of Fender’s effort to use remaining Tolex and grillecloth supplies, or if it was a custom order. But it might be the last Fender thus appointed, barring the rare reverb tank from late ’64.

This article originally appeared in VG’s November 2023 issue. All copyrights are by the author and Vintage Guitar magazine. Unauthorized replication or use is strictly prohibited.