[Heathkit] HW 100 CXR NULL

[Dick KF4NS]

Wow! Sometimes I say things totally from out of left field. Been so 
long since I aligned the rig that I forgot the relationship there. 
After looking back at the schematic again, I see how stupid that 
sounded.

I tried again but the two sideband positions were still far apart. All 
connections were good so I cleaned the pot again but did not put any 
conductivity "improving" solutions in there. This time it was a piece 
of cake to get the sideband positions to almost perfectly match. It 
reads 0.19V RMS now on both. Sometimes it is best to just clean a 
surface and forget the additives.

The balanced modulator diodes were changed to Schottky 1N6263's 
several years ago and it sure improved the audio. That and several 
other mods have made the audio more responsive, less noise and much 
cleaner and clearer. Still love this old radio, of course it is good 
because I built it and cared for it myself. hi,hi

All is well that ends well. Thanks for all the comments.
73, Dick KF4NS
St Petersburg, FL 33714 USA
Keep The Glow!

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at verizon.net>
To: "Dick KF4NS" <kf4nsradio at verizon.net>
Cc: <Heathkit at mailman.qth.net>
Sent: Thursday, July 12, 2007 8:02 PM
Subject: Re: [Heathkit] HW 100 CXR NULL


>> On the LSB null capacitor,
>
> Whoa!
>
> Where did you get the idea that the null capacitor is for LSB only?
>
> It is not!
>
> Nor is the null-adjust pot only for USB.
>
> You have to adjust BOTH of those while switching between LSB
> and USB, and compromise so that you have about equal carrier
> suppression in both modes.
>
> I have found that changing the null-pot for a 10 turn 200 ohm pot
> from Mouser or Newark makes adjusting the null considerably
> easier.
>
> I also use a scope, since that makes it far easier for me to see 
> what
> is happening.
>
> If the null-capacitor is fully-meshed or fully-open, then you have 
> to
> adjust the value of one of the small SM caps in the bridge.
>
> I've also found that you get 1) better carrier suppression, and 2)
> better balance LSB/USB if you change all four of the diodes in the
> bridge to hot-carrier types, also available from Mouser or Newark.
>
> Ken Gordon W7EKB 

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