Usefulness of resistor substitution box for amp design/repair/tweaking?
I'm looking to level up in my sporadic amp building hobby and maybe start an amp repair/servicing side-hustle when I retire in a few years.
I'm thinking about building a resistor substitution box tailored for guitar amp designing, testing and tweaking.
My initial thinking is that this would have three independent resistor arrays, each with a rotary switch to change values. Physically it would look something like the mockup below:
Usage would be limited to low- medium power values:
- preamp plate loads
- preamp cathode resistors
- grid leaks / grid stoppers
- mixer resistors
- phase-inverter resistors
- NFB resistor experiments
- selected bias-network resistors
Electrical limits:
- Max voltage: 500V DC
- Design target: ≤ 400V
- Max current through switch: 100 mA design / 150 mA absolute
- Switching: no live switching
To be clear, I'm not looking to build a decade box - each switch position would have a discrete resistor value and the switch decks aren't cascaded.
Before I get too far down the design rabbit hole I'm wondering how useful this would be in practice?