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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