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[Amps] multi-tube amplifiers

To: <amps@contesting.com>
Subject: [Amps] multi-tube amplifiers
From: "Harold Mandel" <ka1xo@juno.com>
Date: Fri, 26 May 2006 08:54:38 -0400
List-post: <mailto:amps@contesting.com>
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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