On Sun, 04 Jan 2009 21:22:12 -0800, Archimedes' Lever
wrote:

On Sun, 04 Jan 2009 21:06:12 -0800, John Larkin
wrote:

On Sun, 04 Jan 2009 20:58:39 -0800, Archimedes' Lever
wrote:

On Sun, 04 Jan 2009 18:52:14 -0800, John Larkin
wrote:

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


In other words... extrapolated. You take a measure of a voltage,and
calculate (read extrapolate) the amperage.

That's measured, not extrapolated. How do you think your picoammeter
works? Does it count electrons passing?

No, it is a direct reading, and goes directly in the circuit. We were
testing PMT supply leakage.

Calculate is not the same as extrapolate:

Sure it is.

http://en.wikipedia.org/wiki/Extrapolate

"In mathematics, extrapolation is the process of constructing new data
points outside a discrete set of known data points."

Exactly. The current is the UNKNOWN data point. You construct the
value based on data points taken OUTSIDE a direct current reading.

So you "conclude" the value from reading of other types of data taken.
ie extrapolate.

You make a positive effort to be Always Wrong.

You're an idiot, Johnny. You always resort to this stupid remark.


Because you're Always Wrong.


John