But even in the Tweed era some amps shared circuits - the Pro, Super, and Bandmaster were all the same amp with different speakers - 15", 2x10", and 3x10" respectively. The "Tweed" voice was even more mid-forward (or less sucked.) than the "Brown". The "Brown" stack was different, used tapped pots in some locations, and had more forward mids. The way to boost treble in a passive circuit is to cut everything else. Of course the tone stack is lossy, it's passive. And both the Princeton and Deluxe run the 6V6 output tubes at 420V B+ the difference between the 12W Princeton and the 22W Deluxe was that the smaller power transformer in the Princeton would sag under load, even though the idle voltages were the same. Champ and Princeton, by the way, shared the same power transformer. Princeton had a simpler phase splitter design. The Champ-Amp had the same preamp, but being a single-ended 6V6 amp, lacks a phase splitter stage. But if you take a black Deluxe-Amp (non-reverb model), change the outputs from 6V6s to 6L6s, and change the power and output transformers to reflect the needs of a more powerful output section, and add "Bright" switches, you've got a Bandmaster-Amp. There may be small differences in the feedback loop around the power amp stage. And of course the transformers and speakers.
From Deluxe to Dual Showman, the circuits were identical up to the output tubes, plus or minus a few features - Bright Switch, "Mid" control, reverb, those are the only real differences.
This applies across the whole "Blackface" Fender line from Champ-Amp to Dual Showman-Amp. And yes, the fixed value is rather low and "scooped". The two-knob stack IS the three-knob stack, with a fixed value for the "Mid". The only difference between the two-knob and three-knob stacks was replacing one resistor with a pot. Many manufacturers replace the "MID" control with a fixed value resistor.įor AB763-type circuits, the tone stacks were identical, with a few notable exceptions - the bass channel of the Bassman was unique. Also, don't be fooled into thinking that because there is no "MID" control that the 3 pot circuit isn't being emulated in one form or another. There is also considerable loss to the circuit. The two (2) pot stack is usually refered to as a "Brown face" stack because there is little or no change over these "black face" tone circuits and those of the older tweed amps preceding them. It's very well documented that the difference between the 2 pot stack and the 3 pot stack (MID control) is generally considered to be a lack of mid range response, scooped if you will.
First, not all of the pre CBS amps share the same tone stack and a quick look at any of the schematics will show that as well. Lumping all "Black face" era pre CBS Fender amps into the same bucket is just wrong. Bob Leonard wrote on Fri, 13 March 2009 14:17