Adding a Product Detector to a Hammarlund HQ-100A

Important Note:  Before attempting this conversion, know that there are dangerous and potentially lethal voltages involved.  Unless you are absolutely certain that you know what you are doing and have taken the proper  precautions, do not perform this conversion.   I cannot be - nor  will  be - responsible for any injuries or damages incurred as a result of your reading this website. 



    The Hammarlund HQ-100 (and later the HQ-100A) was a very popular Novice / SWL, general coverage radio from the 1960's.  While it was designed for both AM and CW / SSB use, tuning in either CW or SSB signals can be frustrating.  With the HQ-100 version, there was no BFO per se in the radio and the user was instructed to use the 'oscillating' Q Multiplier as a surrogate.  The improved HQ-100A used a separate BFO, but some users complained about a 'weak BFO signal'.

    Since the HQ-100A version was not equipped with a product detector, to tune in either a CW or SSB it was necessary to disable the AVC and then 'ride' the RF gain control while adjusting the BFO circuit to maximize intelligibility.  The same was true of comparable radios from this time frame, including the Hallicrafters S-85, SX-99 and their predecessors, even the venerable SX-28 and the SX-40.

    This website describes how one may modify the HQ-100A with an integral product detector that enables very pleasant CW / SSB reception.  This is not a 'cookbook' type of article wherein every step will be described or a schematic offered.  Rather, it should provide enough suggestions for a competent builder to both install this circuit and then to improve it to suit his / her tastes.  If you're interested, read on..

General Steps

73's - Joe - K3JLS