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I was looking at the photos of the reissue tubes on the Bay, trying to get some idea of the physical differences. Tung-Sol is different from the Mullard (and EH) in that it uses metal supports against the glass, rather than mica. Sonics aside temporarily, I came across a photo of the factory boxes, and the label indicated a Gm of 6,900. Am I wrong, or is this significantly less than "standard" specs for an EL-34? I thought they were in the 10,000 range, give or take.
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Buy Chinese. Bury freedom.
Follow Ups:
You can't look at just the Gm number and tell much. The Gm varies with the tube operating conditions (current and voltage), so you'd need to know under what conditions the number was obtained.
Also the tolerances on tube specs are VERY large - so there is significant variation from tube to tube.
Just FYI - the Tung-Sol tube is really good, I highly recommend them.
Well, there are several reasons why I thought the factory number would be closer to "book" specs than that, but I guess it doesn't matter. Thanks for the advice on the Tung-Sols. They're my choice when the time comes.
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Buy Chinese. Bury freedom.
But realize even "book" specs are rarely met by production tubes. There is the classic bell curve of distribution, with lots of tubes being significantly different than the "bogey" tube the specs were derived from.
Hey - compared to transistors tubes are very tight tolerance. A 2N3055 transistor has an hfe (gain) spec of 20-70, that's a difference of 350% - in the SPEC!!
"A 2N3055 transistor has an hfe (gain) spec of 20-70"
And there there are those darn small signal FETs with IDSS that varies all over the place. Give me a 6SN7 any day! :o)
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Buy Chinese. Bury freedom.
The book value says
gm = 11,000 mA/V at Vak of 265V and Ia of 100mA
gm = 9,000 mA/V at Vak of 265V and Ia of 70mA.
When testing EL34 for Guitar Amp use I use my Avo MKIII.
Max Vak I can dial up is 400V and I test at 45 - 50 mA and at that current they all give a gm around 7,000 mA/V.
I have often wondered if the Guitar Amp crew (me included) are missing a bet. They all run B+ around 430 to 480 V to screw that last possible watt out of the tubes.
I built a "Junkbox Trainwreck" Guitar Amp for a friend, ran a pair of EL34 cathode biased, B+ of 380V (s Vak of approx 350) biased at 60mA. I only got 32 Watts out of the pair (just below the onset of clipping) rather than the 50 to 55W that is normally squeezed out of a pair of EL34 BUT they were 32 glorious watts. The best EL34 PP Guitar Amp I've ever heard.
Cheers,
Ian
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