Note
QST, Sep 1972, p. 115. (probably earlier)
The Model 330 general coverage tuner plugged into the Swan 600-R amateur band receiver and extended its frequency coverage from 3–30 MHz. It had a coverage gap between 5.4 and 5.6 MHz to avoid the receiver’s intermediate frequency. Amateur band coverage using the 600-R’s VFO was chosen with a front-panel switch on the external tuner.