[Amps] Question re GU-74B grid current

[Carl]

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 at vip.bg>
To: <amps at 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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