An early Comet, with it's Hammarlund supplied  electro-dynamic speaker.  It's an eight-tube superhet with on-board AC power supply.  The radio tuned 545KHz to 20MHz using five sets of plug-in coils.  The variable capacitors, plug-in ceramic coil forms, and double tuned IF transformers were all Hammarlund products.

There are two 465KHz IF stages with a total of six tuned circuits.  The middle knob and drum dial are the main tuning control.  The two controls to the right and left provide "vernier" tuning of the mixer and local oscillator.  The toggle switch actuates a fixed-tuned BFO for CW reception.  List price was $130, less tubes and cabinet.

Comet Pro Prototype

The initial Comet "Pro" appears in Hammarlund's ad in April 1932 QST.  "An eight-tube custom-built super-heterodyne which will do all that the professional operator demands between 14 and 200 meters."   The center control with the illuminated drum dial is now band-spread, while the two knobs with circular scales are "band-set" (main tuning).  The type 47 audio-output power pentode has been eliminated in favor of a type 27 triode, and a phone jack has been added to the front panel. NYC Radio Row retailer Leeds offered the Comet Pro for an introductory price of  $88.20 while mentioning a $150 list price.

Production Comet Pro

The early 1930's were a period of extremely rapid development of shortwave receivers.  The Comet Pro underwent a series of changes throughout it's life time.  The schematic for the first major revision is dated September 1932.  The calibrated band-set dials have been recessed behind the panel, and are now actuated by friction-type reduction drives acting on the edge of the dials.   Later Comet "Pro's" were housed in a wrinkle-finished steel case.   The crystal filter model is shown at the right.

Improved Comet Pro

Inside:  A tuning handle has been incorporated into the BFO coil (lower left) to allow operator adjustment.   The plug-in coils are covered by cylindrical shields to limit unwanted coupling.  New IF transformers, tuned by air-dielectric trimmers to acheive better stability, were introduced in late 1932.

Further Improvements

The claims and counter claims expounded in period advertising often make interesting reading.  For example, in October 1933 QST, McMurdo Silver touts that Admiral Byrd has chosen his 5A receiver for his next Antarctic expedition.  Two months later Hammarlund published a testimonial radiogram from an Arctic expedition complete with pictures of a walrus and an Eskimo.

The Comet Pro enjoyed considerable success in the commercial market.  Here's a DC Comet Pro, one of several, modified by AT&T for use as frequency-selective voltmeters to service multiplex telephone circuits.  The added meters read signal level in dB and battery voltage.  Custom coils tuned the LF band.  (N3FRQ Collection)