persistent 60 cycle hum only on tube gear

@erik_squires said:

If the grounding electrode can ever carry power-system fault or surge current, it is NOT a 250.54 auxiliary electrode anymore, so for the sake of audio equipment grounds, no, you aren’t using an auxiliary electrode.  This includes anything that has conductivity to equipment chassis like your amp, cd player, etc. 

Erik,

The earth shall not be considered as an effective ground-fault current path.

NEC 250.4(A)(5)

(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.

"persistent 60 cycle hum only on tube gear"

few steps to debug the problem:

1) disconnect amp input cables, and plug RCA connectors dummies short/small resistance instead.

2) use linear signal isolation transformer 1:1

3) check tube amp for ground leakage, which typically happened in power transformer 

I’m not saying an auxiliary grounding electrode is an effective ground-fault current path — I’m saying it can become an unintended parallel current path during abnormal conditions, which is why assuming small-gauge wiring is adequate is risky. Of all the places where audiophiles should overbuild, grounding is one of them.

I suggest that the argument on Audiogon is moot, what will matter is what the inspector thinks, and good luck getting them to agree it's "auxuiliary" instead of "supplemental."  

If you can replace the electrolytic filter capacitors in the power supplies in the vacuum tube amp and preamp with metalized polypropylene capacitors, they will last forever because they do not go bad even when not used every few years the way the inferior electrolytic capacitors do, they have better ESR, and they self-heal if a leak should happen.