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Has anyone built a 47 SE amp?

Hey guys,

I found some Cunningham 47s. They are quite pretty tetrodes. How would these sound triode strapped? Ultralinear? Pentode?

Any schematics to share? If I were to build an amp with these, I'd like to use all "period" tubes, preferably all with early bases. It'd be quite a fun amp, I think.

As things tend to go..."Too many projects, so little time!"

Merry Christmas!



Paid Member
I have heard a couple of 47 pentode based SE amplifiers, all triode strapped. All sounded very good. I'd recommend you try it, driver and output stage design are more or less as found with the 45, except don't exceed 250V on the plate, OPT primary Z > 5K, and the grid bias is typically around -16V .. I've never experimented with the 47 as I have close to a life time supply of 45s and currently no amplifier that uses them. (My old 45 amp is out on long term loan.)
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Paid Member
They look to be really linear in pentode mode. Triode strapped would probly give less than a watt of output though. http://oldradio.qrz.ru/tubes/foreign/03/47.gif

IIRC you can get at least 1.5W in triode mode and perhaps 2W - performance (again IIRC) is reasonably comparable to the 45. What I can say is that they sound pretty good as triodes in set ups with HE speaker systems.


2008-05-29 2:41 am
I looked into this a while ago because there are some 47 in my drawer. There used to be a japanese site that had the curves for 47 triode strapped, but can't find them any longer. Over in the tube asylum there's quite a bit of info on Garry Pimm's push-pull 47 amp. If memory serves, people weren't exactly impressed with this tube single ended. But if you got the rest of the amp it's easy enough to switch to a different output tube. I plan to try too, since I have a 6gk5->6v6 prototype on the bench.
I am making a pair of adapters right now actually and was wondering if anyone has any idea whether to strap G3 to plate or cathode or ground for triode mode? Or does it make a difference?

Nevermind my haste, just noticed looking inside the tube that G3 is directly connected to the center of the filament.
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