[Heathkit] DX-100 vs DX-100B

[Glen Zook]

The DX-100B uses the 3-section variable capacitor in
the antenna loading whereas the DX-100 uses fixed
capacitors and a 50 pf variable for the antenna
loading.  Heath did have a field modification kit to
change the loading capacitor arrangement on the DX-100
units to a 3-section variable.  Transmitters thus
modified were called DX-100A.  That is why the 2nd
model of the DX-100 was called the "B" model and not
the "A" model.

The DX-100B has two capacitor values changed in, I
believe, the driver circuitry, to improve the drive
especially on 10 meters.  This change is very minor
and I have seen the details of making the modification
to the DX-100.

The DX-100B only has one crystal position instead of
four as in the original DX-100.  However, the single
position can be accessed through the door in the top
of the cabinet whereas in the DX-100 you had to remove
the transmitter from the cabinet to access the crystal
sockets.

The DX-100B uses the "Apache" style cabinet instead of
the larger version of the DX-100.

The DX-100B came with the holes for adding the SB-10
SSB adapter already drilled whereas to use the SB-10
with the DX-100 you had to drill these holes.

Now, there is an approved Heath modification to add a
spotting switch to both the DX-100 and the DX-100B. 
There was a field modification kit available for this.
 The kit also has provision for changing the keying of
the DX-100 and DX-100B to help with chirping. 
However, if you make this modification the VFO runs
continuously when the transmit switch in "on".  If you
happen to use your receiver to monitor your keying
this can be annoying!  You can download these sheets
from BAMA at http://bama.sbc.edu and do the
modification yourself.

The kit came with four-page instructions including a
template for drilling the hole for mounting the
spotting switch.  You can duplicate this modification
fairly easily.

There was a modification kit available from Heath to
add the SB-10 SSB adapter to both units.  This added a
switch on the front panel and two SO-239 UHF
connectors on the rear panel.  Basically you diverted
the driver from connecting directly to the final
amplifier tubes and added circuitry to change the
final from Class C to AB-1 when the transmitter was
switched to SSB.

Frankly, the DX-100B and the DX-100 are basically the
same transmitter.  The changes made to the DX-100B
actually resulted in a slightly lower price to
manufacture (elimination of two switches - the antenna
loading and the crystal selection, 3 crystal sockets,
etc.).  Also, the Apache style cabinet was cheaper
than the older style cabinet (which I personally
prefer - but my 2nd primary transmitter back in 1960
was a DX-100!).

I have a DX-100 in my AM shack.  If you are
interested, there are photos on the K9STH website the
URL of which is listed at the end of this message.

Glen, K9STH


--- wb8owx at fuse.net wrote:

First...what is the difference between the DX-100 and
the DX-100B 

=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco


		
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