I've been measuring the gm of a bunch of 6B4Gs and they seem lower that I would expect - has anyone here tested theirs? If so, what source were they (Russian, US etc.) and what readings did you get?
Thanks
6B4G testing...
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#1 6B4G testing...
Last edited by jack on Sat Dec 17, 2011 2:15 pm, edited 1 time in total.
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#2
I bought a pair ( NOS, Sylvania early 1950's ) from Jan ( AskJanFirst) in Germany, and I noted that the readings on the box were apparently only 75% of standard . Not sure what the test conditions are ( maybe the typical operation point from the RCA sheets ? ) but they were marked at 45 or thereabouts, which I'm guessing means 45mA .
"Once you find out ... the Circumstances ; then you can go out"
#4
If you find a copy of the RCA datasheet such as http://www.hifitubes.nl/weblog/index.ph ... datasheet/ then the spec is 5250uohms for transconductance but really that is nothing more than a number on a spec sheet
If you look at page 4 of the same pdf then you see the transconductance curves and how they vary with plate volts and grid volts... and they vary a lot so finding one with 4800uohms is not in the list bit surprising or worrying unless you are trying to match valves to better than 10% and if you are good luck!
Normal variation when new was 20% - thats +/- 20% too...
James
If you look at page 4 of the same pdf then you see the transconductance curves and how they vary with plate volts and grid volts... and they vary a lot so finding one with 4800uohms is not in the list bit surprising or worrying unless you are trying to match valves to better than 10% and if you are good luck!
Normal variation when new was 20% - thats +/- 20% too...
James