Manufactured by Hammarlund Mfg. Co., New York NY.

In 1931, Hammarlund launched the „Comet“ model, one of the earliest single conversion superhet communication receivers available.
In 1932, the improved version „Comet Pro“ appeared, this set was built in different variants until 1935.

The „Comet Pro“ was replaced by the „Super Pro“, the first prototype was ready in 1935, the model was delivered from 1936, the SP-10 was the ancestor of a long series of shortwave receivers.

• Principle: single conversion superhet, IF 465 kHz
• Operation modes: A1 with BFO, AM (A3)
• Frequency range: 1.2 - 2.6 / 2.5- 5.4 / 4.9 - 10.7 / 9.7 - 20 MHz; optional 545 - 1200 kHz and 18.75 - 37.5 MHz
• Frequency display: Analogue display without frequency markings, band spread dial
• Frequency memory: none
• Signal strength indicator: none
• Signal processing: IF gain, crystal phasing - notch filter
• Features: plug-in coils, band spreading
• Sensitivity: AM (A3) / Selectivity: kHz (-6/-60 dB)

• Mains operation: 115 V

• mm, weight kg

The desktop unit is typically operated with 115 V, it has a hinged lid that provides access to the chassis for tube replacement.

In the centre of the front panel behind a small dial window is the vertical fine tuning scale, the button directly below is the fine tuning knob.

The smaller tuning knob on the right operates the frequency dial behind the right semi-circular scale window „W.L.“ (Wave Length), the left small tuning knob shifts the oscillator frequency „OSC“ (Oscillator Tuning Control), the position is displayed on the left semicircular scale, as a rule both knobs should be in approximately the same scale position.\
The switch for the BFO is located just below the main tuning knob at the bottom centre of the front panel; the BFO frequency can be adjusted using a lever inside the set.

The left rotary control diagonally below the main tuning knob serves as a volume control, the right rotary control diagonally to the right of the main tuning knob as a control for RF gain (R.F. Gain). The switch for the automatic gain control A.V.C. was only added in the later versions.
The switch in the top right-hand side of the front panel activates the crystal filter, which can be used to „notch out“ an interfering signal.

The receiver has the frequency ranges 1.2 - 2.6 (DD) / 2.5 - 5.4 (CC) / 4.9 - 10.7 (BB) and 9.7 - 20 MHz (AA coils), which are selected using plug-in coils; coils for the ranges 545 - 1200 kHz (EE) and 18.75 - 37.5 MHz (XX) were optionally available. The main tuning dial of the receiver, which was developed in 1932, only had a 0 - 100 division; dials with frequency calibration marks only became common years later.

A weak point of the receiver was the lack of an R.F. preamplifier and the high sensitivity to the occurrence of mirror frequencies 930 kHz below the desired signal (especially at higher frequencies); the large signal behaviour could be partially improved with an external preselector available as an accessory.

The signal from the antenna is fed directly to the mixer stage (57) without prior amplification and is converted to the intermediate frequency of 465 kHz with the oscillator signal (58). After two IF amplifier stages (58, 58), the signal is fed to the detector (57), where the signal from the beat frequency oscillator (BFO; 58) is also added for CW reception. A 2A5 serves as the output amplifier; the AVC (2B7), which was only introduced in the 5th version of the „Comet Pro“, also acts on this tube. The audio signal is fed to the connector for a high-impedance loudspeaker or headphones via an output transformer. The set is operated with 115 volt alternating current, as commonly found in the American mains network, and a 80 tube is used for rectification.

see above

• Hammarlund Comet Pro on the website of www.radiomuseum.org