Keith G wrote:



OK Iain, that's good stuff. Have a look at this pic:

http://www.apah69.dsl.pipex.com/keit.../valvebase.jpg

and could you explain what the figures represent and how they relate to your
explanation above.

What does the following stand for:

Ua

Vg2

Vg1

Ia

S

and what do the Voltages tell us? Do they give us the plate voltage. Is that
an amp design thing or a valve design thing?

May heva been in the link, but my nameserver can't find it.

Neither, they are just the conditions that the valve was measdured at.
They would have set the Ua (voltage on anode) to 430v, Vg2 (voltage on
second or creen grid) to 440v, Vg2 (the first control grid) to -36v and
measured the current that flows through Ia (anode current), in this case
31ma. They then would have sorted each valve according to Ia, and those
with the same valye would be caled a matched set. I am guessing the S
could be for measuring transconductance.

If you look at the curve

http://www.mclink.it/com/audiomatica/tubes/el34.htm

And draw a line up from the x axis (Anode voltage, and see where it
crosses the grid curve at the grid voltage, that will give the expected
current (look at the pentode mode one, as g2 is in use).

--
Nick