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Old 25th September 2008, 07:16 PM   #1
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Default Low mu Preamp Triodes as Power Output Tubes

I would like for someone to explain to this newbie why low mu triodes such as 12AU7, 6N1P and 6DJ8 commonly used in preamp stages can't be used for power output tubes.

Since power triodes are sooo expensive, why not use miniture 9 pin tubes?
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Old 25th September 2008, 07:35 PM   #2
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Because their plate dissipation is nowhere near the big power triodes. even the chunky preamp tubes at ~5-7W will barely give you a watt of power. A 300B, in contrast, is rated at 40W, while even a "small" 2A3 is 15W.
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Old 25th September 2008, 07:49 PM   #3
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There is an amp using 10 ECC82 per channel designed by Tim De Paravachini, about 7 or 8 years ago, delivering 20 Watts per ch and I think it's called the V20. It is held in high regard by those who are supposed to know.

Geoff.
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Old 25th September 2008, 07:57 PM   #4
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Last I checked, china 6L6 were still on the cheap.

If you had to abuse a smaller Triode, you can multiply the Gm in
Triodlington with a good audio BJT. Strangely this combo doesn't
run away too easily, as the Triode's intrinsic "Mu" feedback path
lends stability to the Transistor.
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Old 25th September 2008, 08:00 PM   #5
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OK, that makes sense. You have directed my thinking in the right direction. I see that the anode disipation on a 6N1P is 2.2 watts. I assume that is for one of the pairs; is that correct?

The EML 300B is rated at 17 watts. I suppose it would be a tad impractical to use four 6N1Ps as a substitute for a single 300B. Imagine a chassis bristling with 20 miniture tubes. The good part would be that the heaters could be wired in series!!!
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Old 25th September 2008, 09:35 PM   #6
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Quote:
Originally posted by geoff4valves
There is an amp using 10 ECC82 per channel designed by Tim De Paravachini, about 7 or 8 years ago, delivering 20 Watts per ch and I think it's called the V20. It is held in high regard by those who are supposed to know.

Geoff.

OK, now that's what I was looking for. Here is a link to more info if anyone else is interested.

Why not? These are good tubes with low distortion charisterics. And you could use it for a space heater in the winter. I bought ten new russian 6N1Ps for less than $20 so there is little call for timidity.
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Old 25th September 2008, 09:53 PM   #7
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http://hagtech.com/cymbal.html
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Old 26th September 2008, 07:41 AM   #8
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Default 10 x ECC82 in parallel ...

Quote:
Originally posted by geoff4valves
There is an amp using 10 ECC82 per channel ...

Geoff.
Hello

http://triodelington.blogspot.com/

http://www.vintage-radio.net/forum/s...ad.php?t=13624

Kind regards,
Darius
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Old 26th September 2008, 09:32 AM   #9
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Darius,

What happens to Triodlington if grid ever conducts A2?
Do you have a best recommended practice to deal with
or prevent that event/situation?

---------------------------------------------------------------------

Nevermind... If ECC82 grid is same/similar as 12AU7A,
Even if plate gets pulled all the way down to zero...
Grid conduction + Plate conduction never higher than
what would add to a straight line, guess thats stable?
Attached Images
File Type: gif 12au7a.gif (41.5 KB, 384 views)
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Old 26th September 2008, 09:39 AM   #10
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not what you seek, but maybe the path helps

http://www.diyaudio.com/forums/showthread/t-94403.html
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