@ 5 kW plate dissipation a twin GU84B will be more capable than a quattro
GU74B amp.
2 x GU84B can be had for approx Euro 220.-, 4 x GU74B @ Euro 240.-
With approx loaded 3000 V B+ no vacuum caps are needed in the tank circuit.
The main trick will be the input circuitry. For more details see the files
an photo section : http://groups.yahoo.com/group/emtrondx15/
Cheers, Dick
PA3DUV
----- Original Message -----
From: "Harold Mandel" <ka1xo@juno.com>
To: <amps@contesting.com>
Sent: Friday, May 26, 2006 2:54 PM
Subject: [Amps] multi-tube amplifiers
> Gents,
>
>
>
> At some point, running more than one good tube can only achieve
>
> limited results, measured "bang-for-buck" or "steps-in-reinventing
>
> the wheel."
>
>
>
> Many years ago I built a transmitter that used 4 metal 6L6's inverted
>
> in an oil bath for a whopping 125 watts on 40 meters. The project
>
> was a result of late-Friday night yakking at the Bronx Radio Club
>
> (W2FZ). The bunch of high-schoolers who frequented the club
>
> were interested in what we could come up with, and "Radio Row"
>
> was still standing where the World Trade Center would soon
>
> be built, so mil-surplus cheap electronics were still a subway
>
> ride away.
>
>
>
> In the intervening years I found that multi-tube radios (read PA's)
>
> require all sorts of consideration that escalates rapidly with that
>
> next added tube.
>
>
>
> I am still amazed how Denny did so well with the LK-550, running
>
> three 3-500Z tubes.
>
>
>
> However, looking into another project after the dual 8877 amp,
>
> I considered a three-tube 8877. Before plunking down any money
>
> all the usual suspects were grilled. "Why torture yourself?" was
>
> the most frequent reply.
>
>
>
> If I wanted X amount of power, the first consideration was the power
>
> supply. Next, a budget for the RF department. For cheaper an
>
> expenditure for everything a 3 tube 8877 would cost I could build
>
> an AB2 3CX5,000A, and even a 3CX6,000A device.
>
>
>
> Even a dual 4-1000A tube amp was considered. That is a "retro"
>
> project still in consideration, as I would use a microwave oven
>
> door-window in the RF head to show off the tubes. But never a 3 tube
>
> 4-1000A: That's an exercise in futility.
>
>
>
> I would suggest to the builder who is considering the four-tube
>
> 4CX800A device to maybe considering a 2-tube GU-84b if
>
> he's so in love with Russian surplus tubes. Several of our
>
> group have already reinvented that wheel and I'm sure each of
>
> us would help the new builder over the humps..
>
>
>
> Hal
>
> W4HBM
>
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