Transconductance for kt-90 in plain english

speakerfritz · 7th December 2011, 12:49 AM

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 · 7th December 2011, 12:57 AM

Zen Mod posted it for you in PDF.

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

GloBug · 7th December 2011, 01:08 AM

gm = I out / V in

kevinkr · 7th December 2011, 02:11 AM

Quote:

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 · 7th December 2011, 12:35 PM

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 · 7th December 2011, 01:02 PM

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 · 7th December 2011, 02:19 PM

Quote:

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 · 7th December 2011, 04:53 PM

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 · 7th December 2011, 05:30 PM

Quote:

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 · 7th December 2011, 05:47 PM

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.

7th December 2011, 12:49 AM	#1
speakerfritz diyAudio Member Join Date: Jul 2008	Transconductance for kt-90 in plain english 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

7th December 2011, 05:47 PM	#10
Wavebourn Anatoliy Lisovskiy diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	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. __________________ !!!Warning!!! Single Ended Class-A-Holism is addictive!!!

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7th December 2011, 12:57 AM	#2
GloBug Banned Join Date: Jun 2011	Zen Mod posted it for you in PDF. 13.4@250v 10.1@400v pentode 12.7@250 triode

7th December 2011, 01:08 AM	#3
GloBug Banned Join Date: Jun 2011	gm = I out / V in

7th December 2011, 12:35 PM	#5
DF96 diyAudio Member Join Date: May 2007	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.

7th December 2011, 01:02 PM	#6
SemperFi diyAudio Member Join Date: Jan 2002 Location: nowhere	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.

7th December 2011, 04:53 PM	#8
smoking-amp diyAudio Member Join Date: Dec 2001 Location: Hickory, NC	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.