Transconductance for kt-90 in plain english

[speakerfritz]

Hi, I posted this question once before and got a few links to data sheets which did not answer the question. I need to know what the transconductance spec is for a KT-90 in GM. Thanks

[GloBug]

Zen Mod posted it for you in PDF.

13.4@250v 10.1@400v pentode
12.7@250 triode

[GloBug]

gm = I out / V in

[kevinkr]

Originally Posted by speakerfritz

Hi, I posted this question once before and got a few links to data sheets which did not answer the question. I need to know what the transconductance spec is for a KT-90 in GM. Thanks

I assume you mean umho or siemens?

In which case around:
14000umhos in pentode at 250Vp, 250Vs;
8800umhos in pentode at 400Vp, 300Vs;
15000umhos in triode connection at 250Vp

From this data sheet: http://www.mif.pg.gda.pl/homepages/f...084/k/KT90.pdf

GM is not a unit of measure and can be specified in lots of units like mA/V, uS, and umhos (obsolete actually)

[DF96]

And its not GM. Should be small g (conductance) and subscript m (mutual). G is Giga (10^9) and I don't know what M is.

[SemperFi]

M can be Mama, in which case GM is GigaMama and a synonym for mother in law. Or M can be Mega, so we have GigaMega which is synonomous with the common 1000000000000000 integer.

[Alfred Centauri]

Originally Posted by GloBug

gm = I out / V in

speakerfritz:

GloBug has the right idea but that's not quite correct.

g_m is the slope of the I/V curve at a particular DC operating point.

Take, for example, the plot on page 5 of the link in kevinkr's comment. Pick one of the curves, and pick a point on that curve. The slope of the line tangent to that point is the g_m at that operating point.

See attached.

[smoking-amp]

Don't forget that gm varies with cathode current too, roughly as the square root. So there is no "the gm" for any tube. Its a variable you have to measure off the curves (see above) or locally interpolate with the square root rule.

[kevinkr]

Originally Posted by DF96

And its not GM. Should be small g (conductance) and subscript m (mutual). G is Giga (10^9) and I don't know what M is.

Quite right and I glossed over that unfortunately.. M is 1^6

@ speakerfritz, posts #7, and 8 are particularly relevant. Post #6 is just funny. .

[Wavebourn]

GM is General Motors. One of Generals that won Cold War (i.e. benefited from it)

umho is micro mho, mmho is mili mho, mho is backward written Ohm because Ohm is volt/ampere, mho is ampere/volt. I think initially it was a joke.