From the December 2013 Tone Quest Report. Reproduced with the kind permission of the Tone Quest Report.
TQR: The Mark IV is a modern classic with a great sound and all the practical features you could want crammed into a portable 1x12 cabinet. Can you describe how this model has evolved from your earlier work in terms of design, component selection, tone stack and other features? Is this the most ‘evolved’ Goodsell to date?
RG: The evolution of the Super 17 from it’s humble beginnings on recycled organ chassis to the current (and probably final) Mark IV iteration was a fairly linear path that reflected my maturation as a builder. I was about 40 units in to what would be retroactively be known as the “Mark I” before it occurred to me that amp building could be a viable career alternative to wrenching Hammond organs. It would be another 60 or 70 amps before the Mark 2 showed up, which was the solution to the erratic and inconsistent supply of organ parts. It was an off- the-shelf aluminum Marshall 18-watt kit chassis with all of the holes drilled in the right places, and I continued to build the ex- act same 3-knob Super 17 on this platform, which would soon find its way into the Marshall 18-watt style birch-ply combo cabinet that many other small builders have embraced over the years. This combo was the launch pad for most of the innovations that would define later models – it could be a 1x12 or a 2x10, the same chassis could be adapted to the 33-watt models, and it facilitated features like reverb and tremolo, which went through their own process of evolution.
Reverb and Gibson Bias-vary Tremolo
From the beginning, the secret sauce has been in the simplicity, including the single tone control, and I was loathe to add any feature that would detract from the purity of the original signal path. I found I was able to inject the reverb signal on the ground side of the phase inverter, and avoid the signal degradation from doing it the “normal” way, and while it sounds different, it’s effective with it’s own personality. Soon after came the late ‘50s Gibson-inspired bias-vary tremolo, which begs the question why anyone would ever use any other method. Like the reverb, it is not in the signal path, manipulating the bias voltage on the power tubes instead. These two features could be viewed as “modular” additions as either (or both) could be added to any push-pull amp with a long-tail phase inverter with virtually no alterations to the original circuit.
Within a year, 90% of the Super 17 Mark II combos featured both re- verb and tremolo, while most of the heads continued with the basic 3-knob set-up. Several hundred Mark 2 amps were made before any other changes were contemplated, although during that period there was a 10-piece “Clairmont Classic” re-issue of the original amp as I cleaned out a storage unit that still had a few original cabinets and organ chassis. Since I had another 26 Hammond AO-35 chassis available, I needed an enclosure that would work, and turned to the solid pine 5E3 tweed deluxe box (with some modifications) to complete the series that came to be known as the Limited Edition. With only enough space on the chassis for a pair of 12AX7s, the Limited Edition did not have reverb or tremolo, but it marked the debut of the “5/17” (triode/pentode) switch which created a dual power feature.
Mark III
The smaller, lighter Limited Editions sold out immediately, but being completely out of organ hardware at this point, I had to develop a new smaller aluminum chassis from scratch, as the Marshall 18-style was too large to fit into the 5E3 box. The result was the Mark III. Available only as a 112 combo, it was more than 10 pounds lighter than it’s predecessor, and featured reverb, tremolo, and the 5/17 switch as standard equipment. For the first 3 years, the Mark III had a solid-state rectifier in order to make the same plate voltage with a small- er power transformer to save space and reduce heat, but later ones were wired for a tube rectifier, and eventually the GZ34 became standard. At about the same time, a moderate revision to the reverb design eliminated an entire 12AX7, meaning only two 12AX7s (besides the phase inverter) were required for pre-amp, reverb return, reverb send, and tremolo oscillator. Since the pre-amp had always consisted of only a single triode (one-half of a 12AX7), you could take a Sharpie and still trace the original circuit exactly as it was drawn on Serial Number 0001. Despite a major change in packaging and the addition of several new features, the touch sensitivity, responsiveness, the heart, and the soul of the Super 17 remained fundamentally unadulterated.
And so it was for nearly five years the Super 17 Mark III was the bread and butter amp of the entire product line, and to date is the most prolific of all Goodsell amps with more than 500 copies built. The Mark II soldiers on as the basis for every model above 20 watts, including the 33 series, Black Dog, and any build that needs to be a 2x10 or a 2x12, as well as all heads across the board. The larger chassis still requires alteration for every build, including adding and/or enlargement of tube sockets. Meanwhile, the smaller Mark III chassis turned out to be highly adaptable – variations on the 17, the Unibox, the Dominatrix, and finally the Valpreaux are all built on the same piece of aluminum with no additional drilling required.
‘59 Bassman cathode-follower driven tone stack
Last year, while preparing to build myself a ‘59 Bassman clone (with reverb and tremolo tacked on) I became intrigued by the tone stack, it had always been there, we’ve all looked at it a million times, and I had already been using similar Treble/Mid/Bass stacks on the Black Dog and Dominatrix. Whereas these amps had the tone stack in between two gain stages, the second to make up for the inherent losses in complex tone controls, the ‘59 by contrast had a cathode-follower stage pushing the stack from behind. Now at this point I’d been building guitar amplifiers for 8 years, Hammonds and Leslies for 12 years before that, and I never had the occasion to delve into the virtues of a cathode-follow- er. With single-stage pre-amps, single tone controls, and no effects loops I had no use for a current amplifier or imped- ance coupler/buffer – but wait a minute... Is it possible that a cathode-follower-driven tone stack would allow the secret sauce to pass through relatively unscathed? Could I get tone modification without radically altering the signal amplitude (a philosophical mandate) between a single-stage pre- and the phase inverter? Turns out the answer is yes, yes you can, as the cathode-follower amplifies current, not voltage. I’m sure that most senior amp builders have known this fact since their days at The Academy, but to me, it was a revelation, and it would eventually change the way I build amps and how I run the amp business...
Super 17 Mark IV
So at this point, the Mark III chassis still had the vestigial tube hole from the reverb re- design, and it was getting a stainless steel plug for the sake of safety and aesthetics, so the necessary real estate was already there, at least internally. Externally there was two inches of blank chassis on both sides, most of which went underneath the edges of the cabinet’s chassis cutout. I would need to re-claim some of that space in order to expand beyond the six control holes that I had to work with, so a call to the cabinet shop and three weeks later, I had a modified 5E3 with a 13.5” opening. I moved the pilot light an inch or so to the right, and in doing so I returned to the Fender-style pilot light jewel for the first time in five years – thus silencing forever the shrill screams of an entire market segment that had been demanding this change for years (maybe some day I’ll have a light-up logo, too, but not today) and I am absolutely certain that I have sold a number of amps based solely on the fact that they were furnished with a violet jewel. So I moved the input jack the same distance to the left for symmetry, lost the 5/17 switch (hallelujah, I never liked the triode mode) making room for bass and treble con- trols and a 3-way mid- switch. Behold, ladies and gentleman: The Super 17 Mark IV. Adding the cathode-follower was literally cut-and-paste straight from the ’59, it fit right between the pre-amp stage and the phase inverter without any changes at all, except I used a 12AU7 for the cathode-follower instead of a 12AX7.
At the end of the day we have the most technically complex and feature laden version of the Super 17 ever. It would be hard to imagine a practical reason or way to add anything else to this amp, but a Peavey Classic 30 looks like the space shuttle in comparison. Not being confined by any PC boards, we can do anything we want, if you wanted to draw a box around each individual element in the schematic of the Mark IV, the preamp, cathode- follower, phase inverter, reverb, tremolo, output – you could find similar “chunks” individually in amps from Vox, Traynor, Gibson, Matchless, and Fender. There is nothing really new under the Sun in Tubeland. The difference is in the execution, what element goes where and how. Technique, transformers, topology and the accumulation of experience learned from the individual assembly of over 1,000 17-watt amps in the last 9 years is neatly summed up in the Mark IV, and I don’t believe it can be taken any further without compromising that intangible sparkly thing that lives in each one of them.
From the December 2013 Tone Quest Report. Reproduced with the kind permission of the Tone Quest Report.