Hammarlund PRO-310 Receiver

The PRO-310, manufactured from 1955-57, is the rarest Hammarlund receiver. Only about a thousand of these unusual top-of-the-line radios were made, and because of their $595 price tag and brief marketing life, relatively few found their way into amateur usage.

The PRO-310 was available in black/gold colors or grey/silver colors.

 The receiver was positioned as a step up from the Hammarlund HQ-series, but more economical than the Collins 51J- series.

Extensive shielding contributes to the PRO-310's stability and massive (65 lbs) weight.

 It appears to be intended as a competitor to National's HRO receivers, but without the inconvenience of slide-in coil assemblies.

Description: The PRO-310 is a 14 tube general coverage receiver that tunes .550 MHz to 35.52 MHz in six bands. A separate calibrated bandspread dial covers 20% of each band. The receiver is single conversion below 2.2 MHz and double conversion on higher frequencies. The first IF is 1802 kHz and the second IF is 52 kHz.

Unique rotating turret is shown at the top of the photo. Metal compartment in middle of chassis covers the crystal oscillator, and that at the bottom covers the BFO.

Design Features: The receiver weighs 65 lbs and is extremely rugged, in part because of a double-cabinet construction. The most unusual design feature is the rotating turret assembly, visible in the photographs. Each of the tuned circuits in the turret is affixed to a heavy removable ceramic form, which slides into a slot on the turret and is retained by small clips. Silver-plated fingers make contact to the appropriate circuit as the bandswitch is turned. Two stages of preselectivity precede the 6BA6 RF amplifier, and these are series resonant circuits, de-Qed with resistors to match impedances. The receiver has extensive internal shielding, including a metal shield around the rectifier tube (removed in the photo).

Styling: With the curved cabinet giving it an art deco appearance, the PRO-310 styling was a radical departure from other Hammarlund designs. Instead of a slide-in cabinet like that of the HQ-series receivers, the PRO-310 cabinet is fabricated out of five detachable heavy metal panels. The cabinet has a wrinkle finish, and was available in black with gold trim or grey with silver trim. All the lettering on the face plates and knob skirts is engraved.The matching 6 ohm speaker is seldom seen.

Each tuned circuit mounts on a heavy glazed ceramic fixture that slides into the turret and is fixed by retaining clips.

Operating Impressions: The PRO-310 is extremely stable, almost from turn-on, and has extremely crisp, hum-free audio. The three selectivity choices seem well-matched to CW, SSB and AM operation. The skirt selectivity is sharp enough to allow single-signal SSB/CW operation The lack of a product detector is a shortcoming, although the AGC operates in the CW/SSB mode. The double slide-rule dial is a pleasure to use. In a side-by-side comparison, it clearly outperfoms my HQ-180AC, mostly because of improved stability, cleaner audio, and superior tuning.