Chris,
Multiple stages are not required.
Any class AB1 amplifier requires no power to the grid to develop full
output. However, the proper voltage swing at the grid is required. If
you use a tetrode, a link coupled parallel tuned circuit in the grid
will usually provide the required voltage swing.
The downside of such designs is that the grid circuit must be isolated
from the plate circuit and a stiff screen voltage supply (preferably
regulated) is needed. Neutralization is a must and band switching can
be a problem with multiple tuned circuits to switch coupled with the
isolation required.
Since the 'swamped grid' amplifiers and grounded grid designs are not as
prone to oscillation and are relatively easy to 'tame', you will find
more published designs for these type amplifiers and few for the tuned
input designs.
Take a look at some of the single band amplifier designs which avoid the
band switching complexity and you will likely find what you are looking for.
73,
Don W3FPR
Chris Kantarjiev wrote:
[warning thread drift]
The Linear Amp kits seem to need a fair amount of drive. I've been
idly thinking about a linear that would allow me to drive it with
my barefoot K2 and get 600-800 watts out for CW.
I've been told that such things were "common" in the 70s. One description
I was given is
two stages, with a pair of 6CL6 pentodes in class A passive grids,
driving a pair of surplus 4CX250Bs in AB1,a very common design.
0.1W in gives 650W out.
which sort of means something to me, but will certainly start many
evenings of study.
If this was "common", it seems that there should be articles. I haven't
had much luck finding one (there's an article from 1959 that uses
a single 4CX250B). So, how about it, you guys who were there then? :-)
73 de chris K6DBG
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