[R-390] No reception below 8 mhz, transconductance testing

[Tisha Hayes]

That is part of my pet peeve even about transconductance testing of tubes.
If you look up the standard for transconductance test it uses a very low
frequency (somewhere about 1 KHz if I recall correctly). That's great for
testing a tube to work in an audio amplifier, it may not be so great for
something that is running IF (455 KHz) or even RF (up to 30 MHz).

So while transconductance testing does give us some value under AC
conditions it really does not tell us how that tube is going to work at the
operating frequency of the circuit.

I had been tempted (only tempted) to modify my TT-1 for IF-like frequencies
(455) but it would also mean re-calibrating everything to that new
frequency, pretty much invalidating any comparison to the transconductance
values that are on data sheets.

Maybe if it was still 1957 it would be a fine activity, to drive a new
standard for testing tubes for RF/IF operation near their operating
frequency.

The other thing to do would be to build a circuit to test distortion of the
amplifier function of the tube, but then it gets even more complicated when
dealing with gain.


*Ms. Tisha Hayes, AA4HA*



*A sweet romance is not for meI need electricityIf you wanna make me
flipHit me with a micro chip*


*I'll be a diode, cathode, electrodeOverload, generator, oscillatorMake a
circuit with me*
*-- The Polecats*