Fender 6G15 Reverb Layout

[Fletcher Munson]

I'm putting together a 6G15 reverb build and something about the vintage layout has always puzzled me. I've never understood why the controls are arranged the way they are. Why does the Input jack sit between the Dwell and Mixer pots? Were they trying to keep the Input and Output jacks distant from one another? Were they trying to keep wires leading to the board short as short as possible? I can think of a couple ways to layout the controls and the Fender approach makes the least sense to me. What am I missing?

[Reader]

The Fender layout prevents the output signal circuitry from crossing over the input signal circuitry. Seems to me like a good layout of form follows function rather than making a panel laid out like a marketing person would do it.

[Fletcher Munson]

OK makes sense. The input jack needs to be closer to the middle of the board to keep the leads short, and as far to the right (looking from the inside of the chassis) as possible to keep everything away from the power supply. But they didn't want to cross any of the circuitry that feeds the output so they put the Input jack as far to the right as they could, without crossing any wires.

What if you used shielded wire on the input? Would that be enough to prevent cross-talk with the output?

[Reader]

- - - What if you used shielded wire on the input? Would that be enough to prevent cross-talk with the output?

IMO optimizing the layout should be the first goal. Shielding can solve problems but the shielding always stops before the end of the wire so there are always components, connectors and wire ends left un-shielded unless advanced measures are taken. From a construction standpoint shielded wiring is more expensive in materials, labor and time so a commercial company will only use it when absolutely necessary. From a designer's standpoint the shielding adds extra capacitance which may deteriorate the performance of some circuits. So - - - (IMO) work the layout first and add shielding second if necessary.

[Fixer2]

What does the resistor do that is right next to the input

[mhuss]

Ground reference for the input tube grid. Input jacks on old amps often have 1M on the input jacks for this purpose.

[Helmholtz]

Yes, it's the grid leak resistor of the input tube.
It is essential.