[Amps] Why are 833s so Expensive

Mon Sep 27 02:36:56 PDT 2010

Hi Alek - yes, I think that for the "real radio that glows in the dark" the GU81M would take some beating.  I did toy with the idea of using the 'glass'-plus-screen from a microwave oven door as part of the casing for my 4-1000A amp some years ago, but in the end never did so as I lived in an area with weak TV signals and was paranoid about screening and TVI - even though theory told me not to worry.

I do have a circuit that one of the Hungarian guys used for a GU81M multi band amplifier and I'll dig it out, scan it and mail it over to you.  It may give some ideas.

I agree, the Ashes will be an interesting series this time around.

Just for the Yanks on the list who are used to Baseball and thus will find cricket baffling, let me offer a time honoured explanation:

1. There are two teams. One out, one in.

2. The team that’s out try to get the player that’s in, out.

3. When they do get him out, he goes in.

4. Then the next player goes out. As long as he’s out, he’s in.

5. The object is then for the team that’s out to get the second player out. When they get him out, he goes in.

6. This process is repeated for each innings until the team that’s out gets the team that’s in all out.

7. When the whole team is out, the team that was in goes out, and the team that was out goes in.

8. Then they play a second innings until they’re all out. Except one player. He remains not out.... 

cheers

Dave G0OIL

--- On Mon, 27/9/10, Alek Petkovic <vk6apk at bigpond.com> wrote:

From: Alek Petkovic <vk6apk at bigpond.com>
Subject: Re: [Amps] Why are 833s so Expensive
To: "DAVE WHITE" <mausoptik at btinternet.com>, "Roger" <roger at rogerhalstead.com>, amps at contesting.com
Date: Monday, 27 September, 2010, 9:34

At 04:04 PM 27/09/2010, DAVE WHITE wrote:

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

G'day Dave,

Yes, I would envisage a low frequency, monoband amp with the GU81M's.
Dunno about 4 of them. I'm sure 2 will do.

I've always fancied the idea of having a microwave oven door glass and
screen on a large glass tube amplifier. I reckon these babies would look
spectacular in full colour on a cold winter's morning.

The Ashes is the be all and end all of cricket. Eveything else is just
practice. Australia versus England is the only game that
matters.

It really will be a good series and I would of course like to think we
can snatch it back but I think it will be a daunting task, even on home
soil.

Best of luck,

Alek. VK6APK

--- On Mon, 27/9/10, Alek
Petkovic <vk6apk at bigpond.com> wrote:

From: Alek Petkovic <vk6apk at bigpond.com>

Subject: Re: [Amps] Why are 833s so Expensive

To: "Roger" <roger at rogerhalstead.com>,
amps at 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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