[Hallicrafters] SX-100

[James Liles]

Hi Dave:
Sounds like you have the MARK1 radio.  The Mark2 has a double pole switch in 
that (SW5) AM-CW-SSB position.  If your radio is a MARK1 you'll probably 
want to convert it to a MARK2 ; and heres why.  Notice in the area that you 
are working that the Mark1 uses a single pole switch and the AVC is biased 
at +4.5 volts.  The MARK2 uses a double pole switch that turns the BFO on 
and slows the AVC.  Further, remove R46 and R47 then ground P9 of V7.  This 
will engage the AVC at a much lower level.  Next, make all of the changes to 
the BFO circuit, they moved the tap from the grid side of the tank to the 
plate and changed a couple of components.  You get more BFO drive further 
eliminating SSB overload tendencies.  If you make all of the MARK1 to MARK2 
changes, you will think your radio is equipped with a product detector and 
the overall performance improvement will be staggering.  Also, you can run 
the radio with the RF gain at ten without distortion or overload in SSB and 
CW mode.  Lastly, align the 50Kc system at 50.75 not 50.5, better sideband 
rejection and sounds better.

Kindest regards Jim K9AXN

--------ORIGINAL MESSAGE--------------------------
Message: 6
Date: Mon, 13 Dec 2010 16:50:36 -0800 (PST)
From: DAVID ABBOTT <davidabbott2 at verizon.net>
Subject: [Hallicrafters] SX100
To: hallicrafters at mailman.qth.net
Message-ID: <797269.5910.qm at web84203.mail.re3.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

I just finished recapping a SX 100. I have a question on C-112. The 
schematic shows C-112 .5mfd 200 volt connected to the switch am-cw/ssb and 
avc.. The SX100 I?have?shows to be a resistor. The bands show a 20k ohm at 
this location. My question is at any time did the Hallicrafter CO. change 
from a resistor to a capacitor early on in the production of the SX-100. 
Thanks for you help. WB6BIL
?

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