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Transconductance for kt-90 in plain english
Transconductance for kt-90 in plain english
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Old 6th December 2011, 11:49 PM   #1
speakerfritz is offline speakerfritz  United States
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Default 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
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Old 6th December 2011, 11:57 PM   #2
GloBug is offline GloBug  Canada
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Zen Mod posted it for you in PDF.

13.4@250v 10.1@400v pentode
12.7@250 triode
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Old 7th December 2011, 12:08 AM   #3
GloBug is offline GloBug  Canada
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gm = I out / V in
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Old 7th December 2011, 01:11 AM   #4
kevinkr is offline kevinkr  United States
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Transconductance for kt-90 in plain english
Quote:
Originally Posted by speakerfritz View Post
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)
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Old 7th December 2011, 11:35 AM   #5
DF96 is offline DF96  England
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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.
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Old 7th December 2011, 12:02 PM   #6
SemperFi is offline SemperFi  Wake Island
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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.
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Old 7th December 2011, 01:19 PM   #7
Alfred Centauri is offline Alfred Centauri  United States
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Quote:
Originally Posted by GloBug View Post
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.
Attached Files
File Type: pdf finding_gm.pdf (38.8 KB, 32 views)
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Old 7th December 2011, 03:53 PM   #8
smoking-amp is online now smoking-amp  United States
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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.
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Old 7th December 2011, 04:30 PM   #9
kevinkr is offline kevinkr  United States
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Transconductance for kt-90 in plain english
Quote:
Originally Posted by DF96 View Post
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. .
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Old 7th December 2011, 04:47 PM   #10
Wavebourn is offline Wavebourn  United States
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Transconductance for kt-90 in plain english
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.
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