On Sun, 04 Jan 2009 18:09:08 -0800, Archimedes' Lever
wrote:
On Sun, 04 Jan 2009 16:22:44 -0800, John Larkin
wrote:
On Sun, 04 Jan 2009 13:31:34 -0700, Jim Thompson
wrote:
On Sun, 4 Jan 2009 20:08:36 -0000, "Fleetie"
wrote:
http://cgi.ebay.com/LOT%2F2-RAYTHEON...20111004r23386
I'm having a "stupid moment": They are sold as pentodes, yet have
only 5 leads. What about the heaters? Well, the heater connections
must be exposed, else they wouldn't work, so what about the other
2 electrodes?
Martin - obviously missing something
Paste into browser...
tubedata.itchurch.org/sheets/127/5/5886.pdf
...Jim Thompson
Nominal grid current 3 fA.
John
Extrapolated.
Extrapolated from what? No, I'm sure this was measured.
I have seen and used a picoammeter. I have never seen a femtoammeter.
It's easy to measure fet gate or tube grid current, into the attoamps,
thousands of electrons per second. The first time I got my hands on
some RCA small-signal mosfets, I was astounded at the pA gate
currents.
Just make a follower and connect its input to a low-leakage capacitor,
an air cap in the extreme. Short the cap, open it, and monitor the
source or cathode with a DVM. Watch the voltage change with time. Do
the math. Easy.
John