I have some mild/light AC hum from my 6505, so I figured I'd try this thing out:
[VIDEO]http://www.amazon.com/Electro-Harmonix-Hum-Debugger/dp/B000NUXNWE/ref=sr_1_sc_1?ie=UTF8&qid=1323126328&sr=8-1-spell]Amazon.com: Electro-Harmonix Hum Debugger: Musical Instruments[/VIDEO]
Verdict: Pass. It definitely works. I can stand in front of my amp and hold the pickups up to the tubes and there is NO hum, and as far as I can tell, no loss of tone.
Why then, do I say pass? Because it functions like a great noise gate with a really shitty attack time. If I nail a big chord and then mute it, there's a very noticeable half second or so sound that sounds just like a regular noise gate closing. It actually does it all the time, even if there's no hum to "debug". So if you're playing a lot of stuff that's just wide open, it's fine - but if you stop playing (and are recording, for example) you will be pulling big transients out of your tracks on every stop.
I'm going to hang on to it because it's decent enough for in the room jamming (just because I can't stand AC noise), but other than that, do not buy this.
You would have a lot more luck sticking a noisegate in the loop for this application.
Or getting the Peavey modded as they are notorious for AC noise & noise in general.
However i find a gate in the loop works wonders as it also kills any power amp noise too,