Val, I suspect the real reason is that the Russian engineers designed the
tube to a specific military specification and it was rated to perform
reliably at that point.
Part of the problem is the anode structure/cooling fins/socket which create
more back pressure than say a 3CX800A7.The 3CX800A7 is actually
conservatively rated compared to the first Eimac spec sheet which got the
FCC upset. OTOH, Ive run 3 of the 3CPX versions at 5KW out on HF and also 6M
conversions that have been shipped to many countries; they have been
reported as reliable. If that tube had a "ham" rating the dissipation would
easily be 1000W for SSB service
None of the memos I have from Russia to George Badger indicate it is
overated, just the opposite and the Russians suggested not pushing it. I
dont blame the Russians for the rather short tube life when run hard. In
fact the reason to increase by 200W was to justify the much higher idle
current. It appears that Acom realized that and used the 3 stage bias to
restore some of the reliability and/or reduce the cooling/air noise
requirement and that is not in most of the other 4CX800 amps on the market.
In reality the 4CX800 was strictly Svetlana USA market driven as they
realized that intelligent hams would see thru the 600W rating as pushing it
too hard.
Carl
KM1H
----- Original Message -----
From: "Val" <val@vip.bg>
To: <amps@contesting.com>
Sent: Tuesday, October 23, 2012 3:14 PM
Subject: Re: [Amps] Question re GU-74B grid current
Carl,
The 800W labeling of GU74B wasn't fraudent, but a pretty fair. If this
tube was designed by EIMAC, or other western company it would have been
undoubtedly labeled 4CX800. Compare its size, grid and screen to 4CX600
and 4CX1000.
Underrating of GU74B proceeded from the political and economic system in
Russia. It wasn't market driven, there was no competition, the price of
the tube and the price per watt weren't of big importance. However it was
really dangerous for the designers if the tube failed to meet its
specifications. That's why they rather insured their lives by rating the
800 watts tube at 600 watts. This was corrected only 25 years later.
73, Val LZ1VB
Yeah sure. A 600W rated tube fraudently labled 800W to grab US dollars.
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