Dunlop Heil Talk Box How does it work?

Can anyone explain to me how does the Dunlop Heil Talk Box work? What parameter/sensor the tube takes, and how that is translated to effect? Schematics? Technical Papers?

Thanks,

I suppose this kind of attack in response to a joke is what I get for not removing the crosspost to alt.guitar.amps. I feel rather vindicated, though, since Keith just posted a link to the same site that's google's first hit. Of course, he actually did remove the crossposting, so you probably can't see that, I'm guessing.

At least I have the decency to post using my real name.

...

It's the only name that matters. Have you smelled that guy? He lives with a buffalo herad, and bathes once a year, if he feels like it. But he plays a mean harmonica, and has the only Champ that runs off a buffalo chip fuel cell I've heard of.