Heathkit SB102 User Manual

1
Optimizing the Heathkit HW-101,
SB100-102 Transceivers
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 100Ω resistor from jack AB (speaker).
3.) Connect the green wire to terminal strip BA lug 2.
4.) Connect the 100Ω 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.
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Heathkit SB102 Specifications

General

Modes	CW, SSB
Tuning	VFO
IF Frequency	455 kHz
Power Supply	Internal
Receiver Sensitivity	0.5 μV for 10 dB S+N/N
Selectivity	2.1 kHz at -6 dB, 4.2 kHz at -60 dB
Image Rejection	>70 dB

Summary

Conversion to Low-Z Headphones

Low-Z Headphone Wiring Modifications

Details wiring changes for using low-impedance headphones, ensuring speaker muting.

CW Operation Improvements

Improving CW Relay Action Speed

Replaces a resistor to increase sidetone amplifier drive for faster relay response.

Correcting CW Sidetone Leakage

Addresses sidetone audible during receive in CW mode by managing circuit coupling.

Transmit Audio Enhancements

Modulator Audio Frequency Response

Changes coupling capacitor C11 for increased low-frequency response in transmit audio.

First Transmit Mixer Drive Boost

Replaces a resistor with wire to increase drive to the first transmit mixer.

Receiver Performance Tuning

Optimizing Transformer Peaking

Adjusts T-102 transformer peaking for maximum transmit drive, not receive gain.

I.F. Amplifier Screen Gain Adjustment

Changes screen dropping resistor R113 to reduce gain and improve distribution.

BFO and I.F. Drive Level Balancing

Modifies capacitors and resistors to balance BFO and I.F. drive for better audio quality.

IF Filter Passband Alignment

Carrier Oscillator Frequency Positioning

Aligns carrier oscillator frequencies to the I.F. filter slope for balanced audio response.

Crystal Oscillator Frequency Tuning

Uses series/parallel capacitors to precisely tune crystal oscillator frequencies for optimal response.

Metering System Stabilization

Stabilizing S-Meter Zero Setting

Replaces a resistor with a higher wattage version to prevent S-meter zero drift.

Correcting Transmit Meter Zero Reading

Adds a resistor to fix the meter reading below zero during transmit in ALC.