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Re: [Amps] Question re GU-74B grid current

To: "Val" <val@vip.bg>, <amps@contesting.com>
Subject: Re: [Amps] Question re GU-74B grid current
From: "Carl" <km1h@jeremy.mv.com>
Date: Tue, 23 Oct 2012 20:00:01 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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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