>
> If you want a convection cooled tube go with the GU81 which is As nearly
> odd looking as the 833. It's over 10" tall and nearly 5" in diameter. It
> *apparently* can be really abused. The Russians say the only way you
> can hurt it is with a hammer. There's a schematic on the net for a pair
> of them that claims 3KW out for contesting and no fan. I would assume
> the mechanical construction gives each tube a lot of space.<:-))
> Filament is Carbonized Thoriated Tungsten with 12.6V @ 11A
>
> BTW they reputedly put out a good signal and they are cheap!! Sockets
> run more than the tube at roughly $50 Vs $35
>
> 73
>
> Roger (K8RI)
Yes, the GU81M is somewhat legendary amongst the Eastern European crowd. I'm
told that they withstand more abuse than an old Land Rover and keep going long
after conventional wisdom indicates that they should have melted. They're barn
door engineering at it's finest.
I have heard of schematics for a pair of these tubes and recall having one
somewhere around the library here for a single tube multiband amplifier putting
1kw out. This was from one of the Hungarian guys quite some years ago.
The data sheet says that plate dissipation is 450W and up to 600W for short
periods. Output power is rated at >=700W at 2kV anode voltage, 600V G2, bias
voltage -200V, G1 drive voltage of 300V, min Anode current 450mA, max grid 1
current 30mA, max G2 current 220mA). I have heard of people running them at
4kv plus on the anode, though!
I have a scanned PDF version of a book of all the common Russian tube data
sheets if anyone wants a copy emailed. Most of it is in Russian though there's
some English descriptions. You'll get the hang of the Russian eventually! The
book contains the typical operating characteristics and usual curves. Just
email me directly if you'd like a copy and perhaps someone can host the file on
a website for some time as with the Eimac bulletins that I sent around last
year?
As Roger indicates, they're as cheap as chips for what they are. This year at
Friedrichshafen they were going for around 30 Euros apeice, though I remember
buying some for around 10 Deutchmarks each a few years ago (when one UK Pound
was about 3 Deutchmarks) and passing them around various interested parties
here.
One of the Russian military transmitters that I've seen plenty of around
European hamfests ran a pair of these tubes and it was a big box, probably
about 3 feet by 3 feet by 2 feet just for the RF deck. They're great up to
15m, but much less efficient on 10m from what I hear. I'd intended to build a
pair for 160, but came by some good 3CX3000A7s instead and decided to
standardise on that tube instead.
cheers
Dave G0OIL
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