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

[Jim Thomson]

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.  

##  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.  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. 

##  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 ! 

##  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. 

later........ Jim  VE7RF