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Optimizing the Heathkit HW-101,
SB100-102 Transceivers



T he Heathkit HW/SB series of transceivers were very popular in the late 60's through
70's and are fairly plentiful on the used market even today, nearly 30 years later.
This series of modifications will increase the audio quality of both receive and transmit,
improve operation on CW, enhance strong signal handling of the rigs, and make the units
useable with the low-Z headphones so often used today. All of these changes require no
hole drilling or mechanical changes at all, and the rig can be easily restored to its original
configuration at anytime if desired. The text deals with the HW-101, but the changes are
applicable to the above mentioned SB-series as well.


Conversion to Low-Z Headphones:

These rigs are designed to be used with Hi-Z headphones, but if low-Z phones are used
the outboard speaker will not mute completely with the phones connected. To convert to
low-Z phones, make the following wiring changes referring to (Figure 1) of this
document, and pictorial 8-4 (foldout from page 53), and pictorial 8-5 (foldout from page
67) of the HW-101 manual:

1.) Remove the black wire from terminal strip BA lug 2 and reconnect it to lug 3
(ground).
2.) Remove the green wire and the 100 resistor from jack AB (speaker).
3.) Connect the green wire to terminal strip BA lug 2.
4.) Connect the 100 resistor removed in step 2 to lugs 2 and 3 of terminal strip BA.
5.) Remove the jumper wire from lugs 1 and 2 of headphone jack L.
6.) Run a NEW wire along the wiring harness from speaker jack AB lug 1 to the
headphone jack lug 2.

Now the external speaker should mute completely when low-Z phones are used.




1


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Figure 1




Improved CW Operation:

In the CW mode the rig's relays are energized by the CW sidetone amplifier's sidetone
output driving the vox relay amplifier. The audio (sidetone) drive to the vox amp is a bit
on the low side for fast relay action, and at speeds approaching 20 wpm the first dot sent
is heard in the sidetone but isn't transmitted due to the slow relay response time.
Correcting this is a very simple modification