Gibson GA-20 hum

[bmccowan]

I hope the family situation works out ok.
On the probe. For a hum problem you do not need to inject a signal. The hum is your signal. The probe is used to feed the signal to another amp. By going methodically input to output or vice/versa touching the probe to each connection in the signal path. At some point the hum will be present/not present on either side of a connection or a component. Or it may build through the path. The instructions are here somewhere on this site; all you need is a guitar cord, a capacitor, and something to hold the capacitor. I used the body of a ballpoint pen. And armed with a sketch of the signal path you can listen to the level of hum at each point. I have used it to find bad sockets, bad pots, bad caps, etc.
edit - found the instructions for the probe https://el34world.com/Hoffman/tools.htm

[bmccowan]

Diverted,
I hope your family emergency has been resolved positively. My family has had too many of those too. I just wanted to let you know that I finished the octal GA-20 I was working on. Very similar, as you know, in most ways to the one you are dealing with. I have it very quiet and sounding great. So I am sure you can get there. Nothing inherently noisy about the GA-20.