The Fender tube amps use a tone stack circuit (looks like three legs of a ladder) where legs correspond to the treble, middle, and bass control potentiometers.
The way this works is that treble and bass controls work "backwards"... they don't add treble or bass, they only subtract. Full subtraction is when the controls are set to "1", and as you turn them "up for more" they subtract less. In order for this to work the tone stack inserts a 20dB gain stage from which the subtraction operates upon (basically, the signal level is boosted so the shape of the EQ can be carved from it).
The middle tone control does something else - it is the insertion loss compensation, and it acts to raise and lower the level of the entire carved-out shape of the EQ which is why the middle control seems to interact a bit with the other two controls.
The Fender tone stack is "flat" when the middle is full up and both treble and bass are full down. In Fender tone stacks that just have two tone controls (treble and bass), the middle leg of the stack uses a fixed resistor instead of a potentiometer.
All this to make clear what I meant by "bypassing" the tone stack gain - maxing middle and minimizing treble and bass is defeating or using the least of the gain in the tone stack.
The Bright switch is designed for lower volume settings and is connected to the volume control so that its effect is completely rolled off by the time the volume control is rotated to about half way. For Fender tube amp channels without a middle control, the bright switch is still in the circuit, acting "on" all the time, but no switch for it on the control panel, and like the other amps it also rolls off about half up on the volume control. This is why some smaller amps sound brighter (because there is not a switch to turn the Bright off) and so folks figure ways to play with the volume up around half or more, by decreasing volume on the guitar, using input 2 (-6dB), using a low gain tube for the preamp stage of the channel, etc...
Some guitarist think input 2 (-6dB) is the one you use for sound check and then you switch to input 1 for performance...
Seriously, choice of input concerns the way the amp's front end see the loading of the guitar pickups - experiment with both inputs and see if you hear a preference and feel a difference in how the guitar handles and responds as you play.
Charlie Garnett - Franken Tele
Yesterday, 08:52 PM in Guitar, Amps & Gizmos