[volt-nuts] Keithley Electrometer probe

[ed breya]

There is no point to attaching a scope probe to an electrometer, 
which is intended for special purpose measurements, having extremely 
high input impedance and extremely low bias current. The UHF 
connector is insulated with PTFE for very low leakage. If you want to 
use it to its capability, anything hooked to it must be low leakage 
as well - the connectors and cable need PTFE insulation. The manual 
has the specifications and application info you need to figure it all out.

Also note that the 610A, B, and C evolved from all-vacuum tube to 
only the front-end being vacuum tube. I believe the 610D (or maybe 
the C) was the fully solid-state model, using  a MOSFET front-end. 
Again, the manuals for the various versions will show which is which.

I found this out the hard way, paying quite a bit for what appeared 
to be the latest, solid-state model in an auction, and finding out 
later that it was actually one of the older all-tube models - only 
the meter was newer - it was used to replace the damaged one in the 
old model. Since the model designation is on the meter only, you 
can't tell what it really is from the front, so look at the back 
nameplate, or better yet, inside,  to be sure.

Ed