Grounding the grids decreases the excellent IMD of the Heath design and
increases the possibility of instability not addressed by Measures'
voodo science.
The Alinco is very sensitive to VSWR. I wouldnt advise adjusting the
fold back circuit either.
By looking at the position of the slug in the core you can determine if
the coil needs more or less turns and proceed accordingly, or user a
tuner at the input.
Carl
KM1H
----- Original Message -----
From: "pmihnovets" <pmihnovets@comporium.net>
To: <amps@contesting.com>
Sent: Monday, October 27, 2008 6:12 PM
Subject: [Amps] SB-220 Exciter Foldback
> I recently have been re-furbishing a SB-220. It has the
> Harbach
> rectifier board mod and also the Somis parasitic mod. Grids are
> grounded
> directly to chasis with copper. The problem I have been experiencing
> is
> that my Alinco DX 70 is folding back power after running full power
> output.
> ( approx.) 600 watts in the cw/tune position. It also will fold back
> in SSB
> position.
>
>
>
> I have tuned the input slug using a antenna analyzer. I was coached
> in
> tuning the slug by grounding the cathode using two 100 ohm resistors
> and
> pressing the TR relay in manually. I was able to get the slug tuned
> on 80
> at 1.5:1. but still having the issue with the exciter fold-back.
>
>
>
> Is exciter driving the amp to hard with 100 watts??
>
>
>
> Any help would be appreciated.
>
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>
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