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47 tube [message #8415]

Tue, 24 August 2004 22:46

West Valley Joe
Messages: 11
Registered: May 2009

Chancellor

I posted about 47 tubes in SET by mistake. Colin Hester showed some schems so there might be some interest here.

http://www.audioroundtable.com/SET/messages/211.html

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Re: 47 tubes are nice [message #8416 is a reply to message #8415]

Sat, 28 August 2004 16:48

metasonix
Messages: 103
Registered: May 2009

Viscount

As Gary Pimm has found, 47s make excellent audio power amplifiers. Very low distortion as pentodes go. Unfortunately I can't say much for their future availability, they are getting scarce at dealers due to their cult use in power amps, as well as being the output tube in millions of antique radios. Unless someone makes a new version (with decent quality control), I wouldn't make an amp using them.

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Re: 47 tubes are nice [message #8417 is a reply to message #8416]

Sat, 28 August 2004 17:22

West Valley Joe
Messages: 11
Registered: May 2009

Chancellor

Thanks for your input, it's good to know the 47 is a good tube. I happen to have a _lot_ of them. Would a UL circuit be my best bet? Thanks, WVJ

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Re: 47 tubes are nice [message #8418 is a reply to message #8417]

Sat, 28 August 2004 21:20

metasonix
Messages: 103
Registered: May 2009

Viscount

>Would a UL circuit be my best bet?

I doubt you could use them UL and get decent power.
The max rated screen voltage is 250v, and even with
a 250v plate supply, a UL amp would exceed that on the
screen on every positive half-cycle.
Unlike EL34s or EL84s, they weren't
intended for ultralinear circuits.

Gary always ran the screens from fixed DC, and
even though he was running 330v, the tubes
were stood off ground for direct-coupling,
so the screens were always within rated operation.

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Re: 47 tube [message #8419 is a reply to message #8415]

Sat, 28 August 2004 21:22

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

Hi W.V.J; I became intriqued by your choice of the 47 tube as I remmembered I had an old article in Radio Craft Magazine that explains a nice SE direct coupled 47 tube amp. It seems pretty easy to build but uses a 56 or 27 driver tube and it is choke coupled. It is a 5 page breakdown of the amp with schematics and description. Very thorough. If interested it is too much to put on this site so should you like e-mail me and I can scan a copy to you. J.R.

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