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Re: [Amps] drive power

To: "Steve Flood" <>, <>
Subject: Re: [Amps] drive power
From: "Dan Hearn" <>
Date: Sat, 17 Mar 2007 08:15:06 -0700
List-post: <>
Steve, You are fortunate to have some excess drive power. The distortion in
your exciter will be greater at 100w out than it will be at 50 or 60 w out.
Turn the drive down on your exciter. Most modern grid driven tetrode amps
use a swamping resistor at the input. The reason is to avoid having the many
different tuned inputs needed for all of our HF bands. The 813 in GG
configuration is usually connected as a triode and needs a lot more than a
fraction of a watt drive.73, Dan, N5AR

-----Original Message-----
From: []On
Behalf Of Steve Flood
Sent: Saturday, March 17, 2007 7:01 AM
Subject: [Amps] drive power

As I muddle through the understanding of amp design, there is a remaining
topic that is confusing me - in regard to matching drive power to the
exciter (in this case a modern 100w transceiver).

I understand that my 100-w tranceiver should be run at maximum output to the
amp input.  Apparently, this requires a grounded-grid setup to accomodate
the relatively high drive level.   Yet there seems to be many amps that are
grid-driven that require very small amounts of drive power.  Are these amps
not designed to be used modern transceivers?  Are they commonly driven by
homebrew low-power exciters?

In my case I am trying to design a g-g 813 amp.  The only g-g information I
have found is in the Orr handbook which says 25w drive - which I asume is
pert tube.  Do I next assume that I need 4  813's match my transceivers 100w
max ouput level?  With what have folks been driving all those homebrew 2x813
amps over the years?

I've been told I'm wasting a good pentode by using it in grounded-grid.  Yet
the 813 specs say something like 0.2 watts of grid-drive power, which is
obviously (?) not meant for modern transceivers.

Steve, KK7UV

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