6B4G testing...

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jack
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#1 6B4G testing...

Post by jack »

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
Last edited by jack on Sat Dec 17, 2011 2:15 pm, edited 1 time in total.
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IslandPink
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#2

Post by IslandPink »

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 .
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Andrew
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#3

Post by Andrew »

Yeah I've also seen readings of 4800 and thereabouts which seems lower than advertised...which is about 5500 isn't it?
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JamesD
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#4

Post by JamesD »

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 :lol:

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
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