Hello Ian,
Probably my GI7 problem is not so often.
The other tube I have is ok.
The russian tubes helped hams from Europe to
build good and cheap amplifiers.
At the Friedrichshafen hamfest were for sale many russian
tubes, from the glass 20W GU19 to 10kW GU39.
A 2500W dissipation GU78B modern tetrode was
to 250 DM (about $120), also its socket.
It is the same tube used for the DX3 Emtron 4 kW PEP linear.
The UA, UT, LZ and other peoples who had these tubes for
sale had to travel thousands km for being there, so these
prices are very low indeed if we consider this distance
(for me was to 3000 km).
It is interesting the fact that I found there a pair of new
4CX1500B at only 550 DM (about $250) for a RF-110A.
It seems that both of the two powerful armies (US and Russian)
left also something good behind, hi!
Regarding the vapoor cooling described, we have to know
that some very intelligent/capable peoples are there (UA).
Low $ budget tend to many good ideas and home made devices.
Some years ago, when I first saw the Radcom article about
the H mode mixer, I knew that I saw somewhere something
very similar.
A UA used a similar mixer, a half H bridge early in the 80's.
I build a such configuration in '92, using russian low power
KP305D and medium power KP902A MOSFETs, from an
article in the russian "Radio" magazine.
Now these assembled PCBs are in my "junk box", replaced
by the japanese "black box", which I don't use it very
much now.
The amplifiers are the only HM devices that we can still build
in these days, and this is why the amp reflector is
technically the best I found!
73's,
Traian
"Ian White, G3SEK" wrote:
>
> I was thinking about what's needed for low seal temperatures and long
> life. Peter's experience only shows that his tube survives... but these
> Russian tubes have very wide production variations. If the thermal
> contact between the cooler and the anode was as poor as the one that
> Traian describes, then it might need a lot more air. Fortunately the
> tubes are cheap and extremely rugged, so if it breaks you try another
> one.
>
> BTW, I remember some folklore that the Russian hams used to use GI7Bs
> with vapour cooling. They had an open-topped pot of water screwed to the
> anode, and a chimney in the top of the cabinet for the steam to escape.
> They had to remember to pour in more water before it boiled dry... but
> very carefully...
>
> --
> 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.com/g3sek
>
> --
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