On Sun, 04 Nov 2007 18:24:16 -0500, Phil Hobbs
wrote:

Robert Baer wrote:
John Larkin wrote:

On Sun, 4 Nov 2007 04:24:07 -0600, "Tim Williams"
wrote:


I think you have that backwards, grid current should be unquestionably
positive for any voltage above the virtual cathode potential (~ -0.8V
here), rising to miliamperes for positive voltages.

Grid contamination would vary widely with age and use. A hot,
contaminated
grid will emit a few electrons, some being picked up by the cathode,
more
by the plate.

What's the maximum value of negative grid current you've seen across
samples?

BTW, what is the resistance of your meter in the modes used?

Tim


What's the physics of the left part of the curve? Thermonic emission
from the warm grid to the plate or the cathode?

Are there secondary emission effects at the grid?

I haven't thought much about tubes in a long time.

People keep threatening to make a device with a semiconductor
electron-emitting cathode, a vacuum gap, and a metallic anode. That
would be very slick, but none seem to be practical so far.

John

Yesssss!
Ages ago, when i saw an article about a semiconductor designed as an
electron emitter, i wondered when that would be used as a low power
cathode - cut energy requirements in half (roughly)!
**
Thanks for the comments - may be helpful when i sit down to think
about them.

Part of the problem in miniaturizing tubes is that it's really hard to
sustain a good enough vacuum, due to having all that surface area per
unit volume. That's the limiting factor in micro field emitters, for
instance.

They usually have to work in UHV to prevent ion damage and stuff.
Nanotube bundles work OK, for a while, until the ends get flayed off;
they *are* noisy. Nanotips wear out fast, too. There was a diode that
just flung electrons out the junction into space, but I don't know
what's become of that.


Organic LEDs use a layer of (I joke not) metallic calcium as an electron
source.

I hope the humidity seals are good.

John