[Milsurplus] Technical assessment

[pete williams]

 G'day,
I've been waiting for a break in the ... er ... weather, to ask what
might be a fundamental question on tube (valve) behaviour.
I had occasion to check a number of 12 SG7 on my TV7-B tester and
found that a large number had readings of between 10 and 30 when the
listed value was 40 as a minimum.
 Thinking that the test set might be defective, I then tested  a
couple known to have readings of 100--- they came from a U S supplier
and were marked as such. My readings  of these 2 agreed with  theirs.
 Strangely, the tubes I would have discarded performed OK in the radio
with no discernable difference between them and the  high reading  "u
beaut" tube. Tubes were part of a  IF strip.
Question ... why is it so ? I am aware that the readings are a view of
the transconductance and I have  some - not enough ?- knowledge of
what it means.
Having gone thru' tubes over the years and  trashed those that didn't
measure up, am I derelict in duty of care and common sense not to have
put them to the service they were intended for ?
May be the cumulative effect of low reading tubes would have shown up
in ultimate performance of the radio as there are  3 in the IF and a
couple in the RF stages.
Comment pse.?

---
Pete Williams
jupeter@datafast.net.au
METUNG AUSTRALIA 3904