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

[Bill Kirkland]

Never late for change. You could revolutionize the tube industry, ok the vintage restoration industry. (but what would all those audio guys do)

Bill

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Tisha Hayes
Sent: February-18-17 1:03 AM
To: R390A <r-390 at mailman.qth.net>
Subject: [R-390] No reception below 8 mhz, transconductance testing

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*
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