[Amps] GS-35B Efficiency Varies with frequency?

[Carl]

----- Original Message ----- 
From: "Jim Thomson" <jim.thom at telus.net>
To: <amps at 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 at jeremy.mv.com>
> To: <amps at contesting.com>, "Paul Baldock" <pbaldock at 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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