Date: Sun, 23 Dec 2012 16:53:03 +0100
From: "Peter Voelpel" <df3kv@t-online.de>
To: <amps@contesting.com>
Subject: Re: [Amps] GS-35B Efficiency Varies with frequency?
The input impedance of a single GS35B is much lower then that of pair of
3-500Z
73
Peter, DJ7WW
## agreed. A pair of 3-500z is aprx 60-65 ohms..and I think the GS35B is like
aprx 25-37 ohms..so 50 ohm coax is wrong to begin with..
## W8Ji used the parallel rg-58 trick to increase the eff on 10M.. on the
ameritron amps..and the 8877 is already 50 ohms !
## all you are doing by paralleling 2 or 3 x rg-58’s on a tube that is
already 50 ohms is to effectively add C to the cathode.
## In the case of separate switched PI nets for tuned inputs, the 10M C2 cap
can be mounted right at the tube itself, as Paul did..with the
provisio that less C2 is then required for the remaining tuned inputs.
Another method is to mount a 100-200 pf NPO cap at the cathode..
that works very good.
Parallel or triple RG-58 will effectively do the same thing....and is
cheaper. Another method is to not use coax at all....and just run a .01uf
coupling cap from tuned input assy to cathode, like drake did on the L4B...
with the tuned input assy + bandswitch right next to the socket.
## Unless you are on welfare, don’t mess with RG-174.
Jim VE7RF
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