Note
QST, Nov 1954, p. 87. (announced)
Allied Radio catalog 1955 (copyright 1954), p. 189.
QST, Jul 1955, p. 133.
QST, Aug 1955, p. 79. (a few details)
Allied Radio catalog 1956 (copyright 1955), p. 195.
QST, Apr 1956, p. 83. (speaker)
Walter Ashe catalog 1957 (probably issued in 1956), p. 7.
Allied Radio catalog 1957 (copyright 1956), p. 243.
Hammarlund broke with their long-standing design traditions in creating the Pro-310 receiver. Tuning was done using the three large front-panel knobs. The knob on the left is the band switch and moved the coil turret. The slide rule dial has two scales. The upper scale is the "band-set" scale. Its pointer was moved by the center knob and was used for rapid changes within a tuning range. The bottom scale is calibrated in fractional MHz and its pointer was controlled by the right-hand knob through a 200:1 reduction.
The frequency displayed is the sum of the upper and lower scales; 7 on the upper scale and 0.10 on the lower would tune the receiver to 7.1 MHz on 40 meters. The band-spread range changed for each of the six bands and was continuously calibrated from 0.55 to 35.52 MHz. The Pro-310 was double conversion above 2.2 MHz and had a 52 kHz IF. The 13-tube receiver came in a choice of a black cabinet with gold trim or the grey cabinet with silver trim shown here.
