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Re: [Amps] 833A/GU-48 x4 Amp support

To: "Roger (K8RI)" <>, "" <>
Subject: Re: [Amps] 833A/GU-48 x4 Amp support
From: "Fuqua, Bill L" <>
Date: Mon, 27 Feb 2012 16:08:01 -0500
List-post: <">>
My vote is for the GU-81 grounded grid. Looks like folks have been runing them 
that way.
Where can I get some cheap? Sounds like a good project.
Bill wa4lav

From: [] On Behalf Of 
Roger (K8RI) []
Sent: Monday, February 27, 2012 3:34 PM
Subject: Re: [Amps] 833A/GU-48 x4 Amp support

On 2/27/2012 3:03 AM, Fuqua, Bill L wrote:
> I believe he wants 4 glowing plates. Larger the better.
> 4x 250th would work but a bit expensive compared to the Russan 833.
> I once ran 2x 250th in grounded grid driven by a pair of 6146Bs on 20 meters.
> So 4 should work.

The GU-81 is, or was, very popular in Europe, particularly running a
pair of them. I think you'll find it's a Pentode, not a Tetrode. Of
course it still requires the same power supplies as a Tetrode as the
suppressor is grounded. They are rated to 50 Mhz but at substantially
reduced power.  Dr Alex  lists a pair of
them running 3KW without forced air.   Nice thing about them is they
can be run without forced air.  Other than the two connectors on top, to
me they don't look much like an 833.  The audio guys have pushed the
price of 833s well out of reason as far as I'm concerned.

I should have picked a few more up when they were running less than
$20USD each. The ones I purchased were $18 each.  Now they are averaging
more than twice that and the sockets are running close to $50 each.
(Prices vary widely)  I've often thought I'd like to build monobanders
for 160, 75, and 40. *Apparently* they are a tube that can be "abused"
and run well beyond its official ratings.  I have no idea as to it's IM
characteristics, but I did hear a couple groups using a pair of them as
drivers. <:-))

OTOH getting four of the rather massive graphite plates to run a
substantial glow might be pushing a fair amount of power out.


Roger (K8RI)
> 73
> Bill wa4lav

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