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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Low mu Preamp Triodes as Power Output Tubes

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kenpeter

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Joined 2007
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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Captn Dave

Member
Joined 2008
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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Captn Dave

Member
Joined 2008
geoff4valves said:
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.
Click to expand...


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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kenpeter

Member
Joined 2007
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?

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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?
 

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kenpeter

Member
Joined 2007
Wasn't meant to imply that A2 would ever be an intentional
long term operating condition. With a Triodlington there is
plenty more than enough class A power already.

Though I guess with me you can't make any assumptions :)
Probably in the top 10 most likely to try something weird.

I was only looking to see if an accidental hard A2 transient
might make it latch or otherwise go bananas? In your specific
case, it certainly seems it would not.

The parts you selected look very hard to kill. Its still difficult
to believe something so simple needs no extra compensation.
The deeper I research to find the flaw, there just isn't any.
 
S

Sheldon

Member
Joined 2003
Dormant thread, but I'm intrigued by the idea of using a small dht (as in 3A5) as sort of a spud pp headphone amp. The triodlington would give a nice high impedance load line. How to find low Hfe bjt's? I assume that they would need to be closely matched or can the sides be balanced by changing the load resistor?

Sheldon
 
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enzoastro

Member
Joined 2010
Better use 6sn7 if you want a ~20 gain double triode imho, 82's not great performance. I bought a stack of the Russian variant, I think they are 6h8 when Russia first opened up with the same idea. I think a better tube would be the 6e5p, one of the most linear tubes, tough and with a low enough plate impedance that your opt could be cheap and good :)
 
rongon

rongon

Member
Joined 2009
If paralleling multiple tubes is a good idea, and if a relatively high mu is a good thing in an output tube, and if a low ra is a good idea in an output tube, then you'd think a good candidate would be triode-wired 6e5P, or parallel up some 6N6P or 5687.

6N6P was apparently designed for use as a small push-pull output stage. It stands to reason that it would be even better paralleled. How about two PPPP (four 6N6P triode sections in parallel, per side, push-pull)?

Figure on a B+ of about 200V.

Each triode's Ia could be 17mA (3.4W dissipation per plate), so 68mA for four sections in parallel (not unreasonable).

Mu would be around 15x.

ra would be around 3k/4 or about 750 ohms (pretty good). It could use a 3k p-p impedance primary. 5k p-p for better damping.

It would only need about 7V peak at the grids for full output. Easy to drive, but all those grids in parallel will build up some Miller C. Maybe drive it with an LTP made of a 6N6P running at 17mA per triode. The low(ish) voltages lend themselves to an all DC-coupled design.

So there ya go, 10 6N6P's for about 6W per channel output.

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