The original GU74 data sheet stated 600Wanode diss
but the cooling requirement graph was extended to 800W.
For the russian tubes do not exist military and commercially
purpose data or tubes, as the power tubes were intended
for the military only! Even the power approved for the
amateurs should not permit using other than very small
glass tubes.
The anode dissipation is the last to concern about
as the actual limiting factor is phisical (temperature),
so a better cooling (always recommended) may solve
a reasonable increase for the dissipated power, and
for SSB the duty is low and the anode mass is high.
The most important are the grid and screen current
and their dissipated power and the cathode current also.
The first Svetlana 4CX800 data sheet stated that this tube
is the same as the GU74 widely used in the Eastern Europe.
The first commercially made amps using the "new
Svetlana 4CX800" were actually using GU74's.
Probably the GU74 were in great surplus in the early '90's
as other russian tubes also.
After some time, the 4CX800 data sheet did not mention
about the GU74 anymore, but did not state about any
difference also.
A slight change of the anode to ceramic body seal can
be seen at the "new" 4CX800 picture, but no other change,
and some rumour was heard fir the ham community, but
no one could say exactly what change (if any) was about.
Two good GU74's shall do 1.5k without problem.
If you want a good (IMD) and reliable amp, do not use
only one tube.
I saw on the www about 2x GU74 amp at 3kV, 1.8 amps,
450V on the screen and 3300W out.
Now, this is over than any data specs, but may work
(don't ask me about reliability, I can't make any
supposition about), and some russian hams are using
the GU74 for grounded grid service and using 5" and
even lower size muffin fans. I don't recommend this.
Good luck,
73's,
Traian
w9gt@comcast.net wrote:
> ----- Original Message -----
> From: w9gt@comcast.net
> To: amps-request@contesting.com
> Sent: Monday, June 03, 2002 12:33 PM
> Subject: True dissipation rating of GU-74B/4CX800A?
>
> Hello amps enthusiasts,
>
> I am preparing to assemble a home brew amp project using Russian ceramic
> GU-74B/4CX800A tubes. I sure would appreciate some experienced input
> regarding the dissipation ratings of these tubes in the HF range up to 30
> MHz. Why do many of the Eastern European and Russian vendors (and some data
> sheets) for surplus tubes describe them as rated for only 600 watts? The
> Svetlana data sheet, however, describes them as being capable of 800 watts.
> Is there a difference between newly manufactured tubes and the commonly
> available military surplus variety other than the markings and brand name?
> Or, perhaps are these military ratings vs. commercial or amateur ratings?
>
> It seems that these tubes ,if in fact they are analogous to 4CX800As, should
> be capable of 800 watts of anode dissipation.
>
> It is also interesting to note that one U.S. manufacturer of amplifiers
> claims to get over 2500 watts output out of a pair of these tubes. I wonder
> if they are using the surplus variety or newly manufactured versions? All of
> this is leading to a simple question: Would it be a good idea to run two, or
> three tubes in a full legal limit amplifier (1500 watts PEP out) and expect
> reasonably long tube life and good performance over all bands? Of course, in
> consideration of good engineering practice, cost vs. benefits, and reasonable
> efficiency.
>
> Thanks for your input!
>
> 73, Jack, W9GT
>
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