What type/brand coax is correct to use from the input jack to the preamp? I have an early '80s Seymour Duncan Bass 400 ss amp.
Most amps don't bother with coax for internal wiring. Those that do might use 24 ga. BTW, one of the 'improvements' made by CBS to the Fender amp line in the late '60s was to replace much of the internals with coax. General concensus was that in so doing CBS ruined them.
Hi. Why bother won't fly well in this case I guess, so here's my take on the subject. I use RS 360-649 2*22avg on all the "signal" wiring. Why? I got a 100m roll dirt cheap, and most likely won't ever use it all . Use whatever You can find, not likely to matter anyway. Just my 0.02€ Sam