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Transconductance for kt-90 in plain english

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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/frank/sheets/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)
 
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.
 

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this is hilarious. Any other tube, there's a specific number. 8417=25K, KT-88's=11000, el-34=6000, 5881's=5400, etc, etc, etc. But KT-90's is a math formula with conditions and qualifications. So alot of folks say a KT-90 is just a EL-509 with the cap wired to the socket, so that would make a KT-90 have a tranconductance value of 18000.
 
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this is hilarious. Any other tube, there's a specific number. 8417=25K, KT-88's=11000, el-34=6000, 5881's=5400, etc, etc, etc. But KT-90's is a math formula with conditions and qualifications. So alot of folks say a KT-90 is just a EL-509 with the cap wired to the socket, so that would make a KT-90 have a tranconductance value of 18000.

Yeah all of those numbers are valid for just one specific operating condition if you look at the data sheets. The KT90 is in no way special in this regard.

I also posted the numbers you were looking for in an earlier post.. I used the KT90 in a number of amps and found the typical transconductance in my particular application to be around 9000 - 1000 umhos for the early EI tubes I had on hand.
 
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