[AMPS] SB-220 conundrum

[Ed Diyorio]

Check the two (2) wafer switches to make sure they are aligned correctly. 
The coupler between grid and plate tank wafer has a tendency to slip. Make 
sure the plate tank switch is centered on its contact points for all bands. Ed


  01:43 PM 1/18/00 -0500, Pete Smith wrote:

>At 08:39 AM 1/18/2000 -0800, K2VCO wrote:
> >Pete Smith wrote:
> >>
> >> 2.  But on 40m, power output (PLATE and LOAD tuned for maximum) is ~1450w,
> >> grid current ~250 ma. and Plate current ~900 ma.  There is also a fairly
> >> striking difference between the PLATE setting in this condition and the
> >> setting for minimum plate current.  If I tune the PLATE for minimum plate
> >> current and LOAD for maximum output, the figures look much more like those
> >> on the other bands.
> >
> >An off-the-wall guess:  I recall that with grid-driven amps, a big 
> difference
> >between the point of minimum current and maximum output was often
>indicative of
> >improper neutralization -- in other words, feedback from the amp's output
>to the
> >input.  Perhaps in changing the relays, you did something which 
> increased the
> >output-to-input coupling.  Is the braid of the coax from the input relay
>to the
> >cathode circuit grounded at both ends?  I could imagine some kind of stray
> >resonance in this cable...
>
>
>Good ideas, Vic.  As far as I can tell, my relay change should have done
>little to the situation.  If you know the layout of the SB-220, the three
>cables (from the input, to the input tank, and to the output for bypassing
>the amp) are all in their original positions and are their original length.
>  The input relay has some short "pigtails" connecting it to the original
>coax ends, but even when I took them and the relay altogether out of the
>circuit the behavior remained unchanged.
>
>73,  Pete N4ZR
>
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>http://206.102.70.3/search.htm
>
>
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