Date: Mon, 12 Jan 2015 03:38:51 +0000
From: Charles Henry <k4vud@hotmail.com>
To: "amps@contesting.com" <amps@contesting.com>
Subject: [Amps] The genius of ham radio
The genius of ham radio is that hams are brave and practical enough to look
THEORY in the face and then go on with WHAT WORKS. Also, to listen to Mr.
Smith, nod politely, and go on with WHAT WORKS.
As a lofty appliance operator, I live ham radio by WHAT WORKS, not Mr. Smith or
others.
That is my fun, and thank goodness for the great numbers of inventive,
theory-testing/discarding real hams who MAKE IT WORK.
73, Charly
## I think what he is attempting to say is that none of you amp wiz bangs out
there can explain to any of us why the input SWR goes to hell
when coax length from xcvr to amp is changed. I notice the exact same effect
on all 4 of my drake L4B 3-500Z amps. Anything over 3 foot long,
and input swr climbs. Nothing to do with the swr meter in any of my 4 x
yaesus, either, nor either of my array solutions powermaster meters, nor my
bird meters, nor my coaxial dynamics meters. they ALL depict an increase in
swr as coax length is increased beyond 3 foot. No amount of tweaking the
slug in the tuned input on each band will reduce it either. The C1 + C2 caps
are fixed silver micas for each tuned input. Unless they are replaced
with arco compression trimmers, there is no way to get the input swr back down
flat.
## The C1 + C2 values on a drake L4B tuned input are double what they are in
a SB-220. A SB-220 uses an extremely low Q...like a Q of one.
With that low a Q, some SS xcvrs have all sorts of problems with an sb-220
tuned inputs.
## BTW, drakes SAFE procedure to tweak the tuned input slugs is to disconnect
the HV millen plug..1st. Then with just a few watts of drive applied, peak
the
slugs for max grid current. max grid current and min input swr will coincide
everytime. You can also tweak the slugs for min swr....with B+ applied, and
low to normal
drive applied. I see no difference in input swr, regardless of drive levels
used.
## The easy option is to just use the built in auto tuner in the xcvr.
## On my HB GG amps that use a tapped coil, and a pair of adjustable
broadcast caps, input swr is always dead flat,
across all ham bands, Just tweak C1 + C2 for flat input swr.
later........... Jim VE7RF
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