[Heathkit] DX-100B questions / problems

[Glen Zook]

The only provision for using the SB-10 is that the rear panel is already punched for the 2 each SO-239 connectors that have to be added.  In the original DX-100 one has to drill/punch these holes.  There are no circuitry changes made in the DX-100B when compared to the DX-100 for adding the SB-10.  These changes have to be made in both models to use the SB-10.

The other changes in the DX-100B are, obviously, the cabinet.  Then the MK-3 continuously variable loading kit came standard in the DX-100B whereas had to be added to the DX-100.  Next, there were 3 capacitor values changed in the driver circuit of the DX-100B to slightly increase the drive on 10-meters.  Finally, the 4-position front panel crystal switch in the DX-100 was replaced with a single slide switch which has to be activated by opening the door in the top of the cabinet.  Of course, the number of crystal sockets was reduced from 4 to 1 in the DX-100B.

The original DX-100 manual can be easily used to work on the DX-100B.  The information on the MK-3 antenna loading kit is readily available including on my website at

http://k9sth.com/uploads/Heathkit_DX-100_mods-1.pdf


This information includes the modifications that have to be made to use the SB-10 with the DX-100/DX-100B, the MK-3 loading kit, and the "improved keying" modification which includes adding a spotting switch to both the DX-100 and the DX-100B.  Also included is the voltage chart measured at the tube pins which was NOT included in any DX-100 or DX-100B manual.

All that aside, the VFO in the DX-100/DX-100B is not really suited to use on SSB because it is just not that stable.  For short contacts you can get away with it.  However, for relatively long QSOs the stability is marginal at best and that is "being kind"!  I definitely tried to use an SB-10 with my original DX-100 back in the mid-1960s.  Frankly, because of the stability of the VFO, this did not "work out".  Then, I modified my MT-1 Cheyenne transmitter, which has the same VFO circuit as the TX-1 Apache, to use with the SB-10.  Although only having 1 each 6146 in the final amplifier, this modification worked out very well and I used the modified MT-1/SB-10 for many SSB contacts.

The wires running through the chassis are a modification to add neutralization per the neutralization circuitry used in the TX-1 Apache.
 
Glen, K9STH


Website:  http://k9sth.com


________________________________
From: Rick Poole <wa1rkt at arrl.net>
To: heathkit at mailman.qth.net
Sent: Sunday, November 13, 2011 8:00 PM
Subject: [Heathkit] DX-100B questions / problems


I have had no luck in locating my manuals for the DX-100B and the 
SB-10.  A couple of people on this reflector very kindly emailed me 
copies of the mods.dk manual for the DX-100 (non-B), but 
unfortunately large portions of that manual, including virtually the 
entire construction section, are missing... and anyway the DX-100 has 
a lot more differences from the DX-100B than I thought.

So I hope it's OK with you guys if I ask some RTFM-type questions... 
I will be ordering another manual but it'll be several days before it 
gets here.

I'm told, I think by somebody on this reflector, that one big 
difference in the DX-100B is that it is specifically set up to use 
with the SB-10 sideband adapter.  On the back apron are three coax 
connectors, two of which are labeled "Out to SB-10" and "In from 
SB-10", and an octal accessories socket that also connects to the SB-10.

Also, another question... There is a piece of heavy wire that runs 
from the Driver variable capacitor, through a grommeted hole in the 
PA shield, and then runs over to the space between one of the 6146's 
and one of the transformers (the modulation transformer, I 
think)  There it stops, with the end hanging in free air, and doesn't 
connect to anything, and isn't anywhere near anything that looks like 
it should connect to.  Is that some kind of neutralization gimmick or 
something?