This tube is likely the thing that's rectifying stray RF that happens
to come along for the ride so I suspect that the problem this guy is
having is more likely to be shielding or grounding issues. The source
of the RF is an open question, but I think it's a moot point because
he seems to be getting a lot of RF from a number of sources which
tells me there are some serious issues with his wiring. I would
entertain the theory that this tube is needing some neutralization and
may be doing some serious oscillation under certain external
conditions, but I wouldn't undertake a technical discussion of how to
fix that on Usenet given there is likely some 900 volts involved here
and somebody could get killed.

-= bob =-

On Sep 17, 2:19 pm, "Richard Crowley" wrote:
It is being picked up directly by two Royer ribbon
microphones which contain an active impedance-
matching circuit implemented with a tube ("valve").
No IF involved there.