75A-4 and KWS-1
Collins 75A-4 and KWS-1, the Gold Dust Twins of amateur radio.
The 75A-4 and KWS-1 are an amateur radio receiver and transmitter pair made by the Collins Radio Company of Cedar Rapids, Iowa. Introduced in 1955, they were designed to operate using the then new single-sideband (SSB) voice modulation as well as CW and AM modes, and were influential in popularizing SSB.
- Manufacturer
- Collins Radio Company
- Location
- Cedar Rapids, Iowa
- Introduced
- 1955
- Original price (pair)
- over $2500
- Transmitter power input
- one kilowatt
- Final amplifier tubes
- pair of 4X150 power tubes
- Nickname
- Gold Dust Twins
Lore & Background
The KWS-1 transmitter and 75A-4 receiver together cost over $2500 when new, equivalent to over $20,000 in 2012 dollars. Collins products at the time were considered 'top of the line', and ham radio enthusiasts nicknamed the pair the 'Gold Dust Twins' because they were unaffordable for most amateur radio enthusiasts when first introduced. Both radios used vacuum tubes and employed Collins innovations including mechanical filters and permeability tuned oscillators. The KWS-1 final amplifier used a pair of 4X150 power tubes and operated at a power input of one kilowatt, the maximum allowed under Federal Communications Commission (FCC) regulations at the time. The transmitter appearance matched the receiver, but its high voltage power supply was packaged in a separate pedestal.
Reader's Guide
The 75A-4 and KWS-1 pair is significant for its role in popularizing single-sideband modulation in amateur radio. In a 2006 review of the half-century-old 75A-4, Stu Cohen wrote that performance under all but extremely crowded band conditions is still excellent, and that a 75A-4 will hold its own against almost any receiver. Under less crowded band conditions, he noted, the performance is superb. This enduring assessment reflects the design's lasting quality and the influence of Collins innovations such as mechanical filters and permeability tuned oscillators. The pair's high cost at introduction—over $2500—underscored its status as top-of-the-line equipment, and the nickname 'Gold Dust Twins' captured both its desirability and its inaccessibility to many amateurs. The KWS-1's one-kilowatt power input, the maximum allowed by FCC regulations at the time, further cemented its reputation as a premium transmitter. Together, the 75A-4 and KWS-1 represent a milestone in amateur radio technology and remain respected by enthusiasts decades after their debut.
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