low grid current vacuum tubes (fwd)

[Steven Roys <sroys@xxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 24 Oct 2003 20:37:47
From: David Dameron <ddameron@xxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: low grid current vacuum tubes

This is more a low current question than high voltage.
Does anyone know where I can find a schematic of a RCA WV-84C microammeter,
or something similar? It is from approx. 1962.
I don't have one, but am interested in what circuit they use. It's specs
are for current ranges from 0.2nA to 1mA, full-scale.

I have been experimenting with several receiving tubes at low operating
voltages to find a low grid current point, and have not had good results. I
have measured input resistances on the order of only 100 Megohm, or several
nA.
David D.