BFoelsch wrote:
On Sun, 04 Nov 2007 15:35:36 -0800, Robert Baer
wrote:


flipper wrote:

On Sun, 04 Nov 2007 03:10:04 -0800, Robert Baer
wrote:



Some 12Au7 tubes have "unbalanced" triodes when viewed this way,


If you mean the two triodes in one bottle are not 'identical' that's
typical. They're not solid state devices made on a common substrate
with the same process parameters, they're individual mechanical
structures that happen to be placed inside the same envelope but
'triode a' in tube 1 could just have easily ended up in tube 2, or
tube 202.



and
some triodes are rather "peaky" like this one.
Shouldn't there be no peak if the tube was perfectly OK?
What would be the cause?
(BTW, data taken using $3.49 Cen-Tech DVOMs from Harbor Freight, one
used for each grid, and one for the plate via a switch)


I'd be skeptical of that data because direct grid measurements are
notorious for altering grid bias.

A normal tube will have a small grid leak until Vgk approaches 0 and
then it turns positive, like a diode (in theory right at 0 but it
depends on the actual field around the grid and that varies depending
on the structure) )

What 'problem' are you trying to solve?

See the top curve where i have calculated the grid voltage WRT cathode.


Your calculations appear to be inconsistent with the info given. For
example 141 nA through 1 megohm generates 0.141 volts, not 14.1 volts.
The whole table looks like it was calculated based on a 100 megohm
grid resistor, not 1 megohm as stated elsewhere.
Check; has been corrected - see previous posting and most recent.