An interesting tube you might want to play with is the GU43b. About half the
price of a GS35b ($65 USD) and 1000 watts plate dissipation. It's a tetrode so I
used the swamped grid configuration. UR4LL seems to have the best price. Sockets
are expensive, but since it uses concentric ring terminals, a clever machinist
could avoid a socket entirely by using homemade spring clamps.
Pix at
http://www.zeitmann-tubes.com/MilitarySurplus/NosRussianMilitaryTubes/GU43B.htm
which is a beautiful picture by the way. I downloaded the picture and used it
for a desktop background. Gorgeous. :-)
Some schematics at
http://pa0fri.home.xs4all.nl/Lineairs/Frinear1500/FRI1500eng.htm
I built an amp with one of these and it worked but with a couple of caveats:
1. Although they are rated to 3.3 kVDC anode, they tend to arc with that much
voltage. Several European hams have confirmed the same thing. Hold the DC down
below 2.5 kVDC or less. The only PS I had was 3 kVDC so I gave it up.
2. There are two different base styles, differing in the center pin. Be sure to
get a matching socket when you buy the tube. I got a mismatched socket and was
able to fabricate a new center pin but it was a hassle. Get the right one to
begin with, or make your own connectors.
You should be able to push a single tube to 1500 watts out but that leaves
basically no headroom. If I were to do it again I would use two in parallel and
hold the HV down to 2.0 kVDC or so. Lots of headroom.
I'd be interested to hear from anyone who has built an amp with one or two of
these.
73, Bill W6WRT
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