Shielded cables

[Swampertech]

Are all "long" runs (2"-5") in the circuits before the phase inverter less likely to pick up hum if shielded cable is used?

[shooter]

generally anything past V1 has a large enough signal not to cause problems as long as you use best practices.
shielded wire from input to V1, and sometimes TS out to TS recovery tubes is where I typically use it.  Remember, only ground ONE end of the shield, usually at signal source

[Swampertech]

Thanks Shooter. I'm building a cascaded front end, with the Lead Channel (Rob Robinette) being switched into the Bright Channel through a relay. I have the relay located as close to the input channels as possible. Would any cathode lines need to be shielded?

[shooter]

any cathode lines

anything  signal < ~ 100mV I'd consider shielding.  I'm not a fan of relays n switches so you'll have to see what other successful amps do.

[Swampertech]

Shooter,, one quick question. To troubleshoot noise in the preamp section section of a 5E3, is it acceptable to ground the grids of the 12AY7 to eliminate each section?