Hi Folks,
I would like to build or buy a tuned input network
(160M-10M) for an amp running a pair of 3CX800A7's. Here
are my thoughts so far. Comments appreciated.
Buy:
So far, I haven't found anyone on the web building and
selling tuned input networks suitable for this application.
I could probably just buy one of those LDG units that was
mentioned on the AMPS List the other day, but it seems like
overkill. After the values for the input matching network
are know and set, they most likely won't change so an
autotuner seems to provide features that aren't really
necessary. Then again, for $125 maybe, it may be worthwhile
in the long run.
Another thought would be to buy a tuned input board for an
existing commercial amplifier such as the Ameritron AL-800H.
I'm not sure how much it would cost, but it runs a pair of
3CX800A7's so it would most likely work fine.
Are there other "buy" alternatives? I called Omega
Electronics and they apparently don't have any more tuned
input boards on hand.
Build:
Building a tuned input network seems pretty straightforward.
A switchable PI network with tunable slug inductors seems
like a good approach. I'm assuming that the input impedance
for the tubes would be approximately 25 Ohms so I would be
looking at matching 50 Ohms to 25 Ohms from 160M through
10M. Shooting for a Q of 2-4 I should be able to use a PI
network calculator to get the proper component values.
Sound about right?
Another approach would be to build the network utilizing the
same component values as used in the AL-800H or other 2x
3CX800A7 amplifier input circuit?
Am I overlooking any other build/buy alternatives?
73, Bob K6ZZ
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