The GU81Ms do indeed have a good reputation here in Europe as being a tube that
can withstand fearful abuse. They keep on working long after they should have
melted. I bought a load of these things for about 10 Deutchmarks each 10-12
years ago and never did anything with them (I got some 3CX3000A7s instead), so
sold them on to a Tesla Coil builder not too far from here. I hear the same
takes of indestructability and barn door engineering from him too.
I understand that the GU81Ms are good up to about 21MHz but are less efficient
above that. I'd intended to use four of them in a topband amp, so high
freqency efficiency wasn't really a design criterion for me.
I hope to hear VK6APK as an S9+ signal on a frequent basis :-)
BTW Alek, what are your thoughts on the upcoming Ashes series - will you be
following it? Apparently England are rated 11/8 to retain the urn - though I
think that's a bit optimistic from our side!
cheers
Dave G0OIL
--- On Mon, 27/9/10, Alek Petkovic <vk6apk@bigpond.com> wrote:
From: Alek Petkovic <vk6apk@bigpond.com>
Subject: Re: [Amps] Why are 833s so Expensive
To: "Roger" <roger@rogerhalstead.com>, amps@contesting.com
Date: Monday, 27 September, 2010, 4:13
Yeah, I've just bought 4 GU81M's and Dr Alex is posting me a pair of
sockets as I write.
Should be an interesting project. . . . if I can ever find the time.
73, Alek
VK6APK
At 08:28 AM 27/09/2010, Roger wrote:
>Subject pretty much says it all. 833s are running over $125 ($258 for a
>pair) each although they vary from $100 to $200 each on e-bay. I don't
>know if they are selling any, but the price has been that way since last
>spring.
>
>OTOH the RUSSIAN GU-81s (similar to, but not quite as strange looking as
>the 833) are running from $22 to over $100 (typical $35 to $45 USD) plus
>shipping which is roughly $20. Now there is a monster that will help
>heat the shack with it's warm glow. <:-)) A pair is good for close to
>the legal limit out without forced air. OTOH they are definitely not
>the first choice for VHF.<:-)) Still, a pair would look great running
>in a glass enclosure.
>
>73
>
>Roger (K8RI)
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