----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Tuesday, December 25, 2012 3:57 AM
Subject: [Amps] GS-35B Efficiency Varies with frequency?
Date: Thu, 13 Dec 2012 11:02:23 -0500
From: "Carl" <km1h@jeremy.mv.com>
To: <amps@contesting.com>, "Paul Baldock" <pbaldock@frontier.com>
Subject: Re: [Amps] GS-35B Efficiency Varies with frequency?
That is characteristic of a tired tube and the poor PS regulation doesn’t
help.
Carl
KM1H
## neither a tired tube nor lousy PS regulation has anything to do with
eff. If a
tube is ‘soft’..... you just can’t pull normal plate current with it...or
way more than
normal drive is required.
** I dont see the original post but I believe the PS was dropping 800V under
load, that makes a big difference in key down power as the load line and
even the input match changes. A soft tube just adds to the confusion.
## as far as PS regulation goes.... the real no load B+ is what you end
up with, with
the amp keyed, NO drive applied, and drawing normal idle current.
** The real no load B+ is in standby with NO LOAD and with a good supply it
should barely budge for a GG triode. Tetrodes are a different case.
Now that does not apply
to bi state or tri state EBS schemes. The point is you have to draw
normal idle current 1st, b4 you
can apply drive, so if the B+ is 100-300vdc more on RX than it is when
keyed, but not driven, who
really cares ? On SSB it’s even less of an issue, since on ssb, we are
only interested in dynamic regulation
not static regulation.
** 700-750V of "dynamic" regulation sucks.
## I find it amusing that most 6m monoband amps will have way better eff
than using the same tube in a
multiband HF amp on 10m !
** I found that out in the mid 60's with the first SB-200 I converted; it
went from 650 to 800W. The first conversion was a NCL-2000 and there was no
change since it was swampd grid, used 500 MHz rated tubes and didnt waste RF
in a high Q tank; 1200W in either case.
## The secret to good eff in a GG amp is in the tuned input
setup..including stray tube C, if any fixed
caps are used at the cathode, and or if parallel coax is used from tuned
input assy to cathode. If the
tuned input is close to the cathode, the coax can be eliminated.
## I have found that PI nets work best for GG tuned inputs, even with
real low Z tubes.
We have had no success with T networks on 6m GG amps, using 2 x series
coils and a variable cap.
Tweak the values of both coils all you want and you can never get the swr
flat on them.
** Only time I had a T work well on 6 was an Alpha 76CA and the LK-800's I
often do. Both are 3 tube amps using 8874 and 3CX800 respectively. OTOH it
also works fine on the 3CX1000A7 2M amp.
Carl
later........ Jim VE7RF
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