Date: Mon, 5 Dec 2016 19:04:24 -0600
From: Mike Waters <mikewate@gmail.com>
To: Fern Rivard <crc@cyberlink.ca>
Cc: "amps@contesting.com" <amps@contesting.com>, Joe <nss@mwt.net>
Subject: Re: [Amps] triode vs tetrode
If that's the amp design I'm thinking about (4CX250B), it's a terrible
design. It was notorious for splatter and distortion.
With 813s, maybe it was OK.
73, Mike
www.w0btu.com
On Mon, Dec 5, 2016 at 6:54 PM, Fern Rivard <crc@cyberlink.ca> wrote:
> A better way yet is to go G2DAF
## several 4 x 4CX-250B amps were built locally in the 70s... all in G2DAF
format. The trick in getting the IMD tamed was that screen circuit. The
precise
value of screen cap was required, or it went all to hell. I still have my old
2 x 4-400A G2DAF amp, recently modified to include 160M. It uses
a 200 ohm non inductive resistor in the input with a 1:4 un-un. Nobody
can hear the difference between it and my 3-500Z amps. Again the screen
circuit has to be dead on perfect. A fellow in W7 land, 22 miles away from me,
also has a 2 x 4-400 G2DAF amp. I dont hear any splatter on his signal, when
tuned off freq.
## I would not recommend the G2DAF config however. Its difficult to make it
optimized correctly. If you have 4-400s, or 4-1000s, its easier to just bond
the grid + screen to the
chassis. Another old fellow, a few miles north of me, used a 4-1000 in G2DAF.
The 6x4 rectifiers were replaced with SS devices. It ran just fine, no splatter
off freq,
but it too, was a bitch to get optimized.
## On my 2 x 813 amp..and also my old 4 x 813 amp, I ran it as a high mu
triode, and just
bonded the grid + screen to the chassis. 1.1 kw pep out of the 2 holer
version.
Jim VE7RF
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