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)
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.
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.
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.
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.
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. . 😀
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.
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.
Not sure what the original provenance of mho was but your explanation makes sense. The unit has been replaced with the Siemen, and that could be a joke too.. 😀
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.
speakerfritz, the g_m of the KT-90, at a particular operating point, exists. If you wish to discover it, make an effort to do so. If not ...
Last edited:
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.
- Status
- Not open for further replies.