Note
QST, Mar 1955, p. 80.
QST, Mar 1955, p. 111.
QST, Apr 1955, p. 3.
QST, Jul 1955, p. 2. (details)
Allied Radio catalog 1956 (copyright 1955), p. 199.
QST, Jul 1956, p 2. (optional gear reduction tuning knob)
QST, Sep 1957, p. 2. (stability, with charts)
QST, Feb 1960, p. 141.
One half of the so-called "Gold Dust Twins," together with the KWS-1. The last of the A-line receivers was tailored for single sideband operation. It broke new ground on several design fronts, not the least of which was its passband tuning system. A front-panel knob rocked the PTO housing, causing the filter passband to pan across the 455 kHz IF. This selected either upper or lower sideband, as well as helping to dodge interference. The 75A-4 employed 22 tubes and included features such as a Q-multiplier notch filter, 1 kHz calibration, a noise limiter, and selectable AVC. Most of the later models incorporated a 4:1-reduction main tuning knob. The receiver came equipped with a 3.1 kHz mechanical filter, and space was provided for two others from a range of bandwidths that included 0.5, 0.8, 1.5, 2.1, and 6kHz. It covered the 160, 80, 40, 20, 15, 11, and 10 meter amateur bands. During the course of its production, the A-4 underwent several minor appearance and circuit changes. Early versions used a smaller, non-vernier main tuning knob. Readily apparent differences also included variations in the S-meters, a change in the frequency range covered on 15 meters, movement of the AM/CW-SSB switch label to line up with that of the noise limiter, and renaming the Dial Drag knob Dial Lock. Between March 1955 and October 1959, nearly 6000 75A-4s came off the assembly line. A number of these, probably fewer than 2000, were made by the Collins facility in Toronto, Ontario. In comparison, production numbers of the KWS-1 transmitter totaled about 1600.
References
A converter for general coverage. CQ, Sep 1962, p. 44.
A wideband filter. CQ, Jan 1964, p. 50.
Additional improvements. CQ, Sep 1966, p. 37.
Adding a product detector. CQ, Oct 1966, p. 29.
Improving overload response. Ham Radio, Apr 1970, p. 42.
General Improvements. Ham Radio, Dec 1974, p. 24.
AVC Mod. Ham Radio, Sep 1975, p. 63.
Increased selctivity. Ham Radio, Nov 1975, p. 70.
