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the Hallicrafters Co., Chicago

SX - 42

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überarbeitet am 19.10.2010

As a successor of the venerable SX-28, a prewar construction, Hallicrafters presented the SX-42 All Wave Receiver in 1947. The double conversion was the top of the range set of the first Hallicrafters post war receiver generation. According to the X in the model designation, it is equipped not only with coil but also crystal filters. It was the receiver with the most extended band coverage available in the early fifties.
The prototypes of the SX-42 came with five bands and a coverage up to 55 MHz. When the FC decided to move FM broadcasting not into the 2 m band, but in the 88 - 108 MHz range, the Hallicrafters engineering team decided to add a sixth frequency range up to 110 MHz, so that FM bradcast was also covered.

SX - 42
1947
Single conversion, 540 kHz - 110 MHz, 110 - 125 V, 110 W;
15 tubes (6AG5x2, 7F8, 6SK7, 6SG7, 6H6x2, 7H7x2, 6SL7, 6V6x2, 7A4, OD3VR/150, 5U4G)
SX - 42 U identical set, Universal transformer
110/ 130/ 150/ 220/ 250 V
SX - 43 / SX - 43 U
1947
Single conversion, 540 kHz - 44 MHz AM, CW; 44 - 55 MHz AM, CW, FM,
86 - 109 MHz FM, 11 tubes. The "little brother" of the SX-42 leaves a gap in the 55-86 MHz range, not all reception modes.
SX - 62 / SX - 62 U
1949
Single conversion, 540 kHz - 109 MHz, AM, CW, FM only 27 - 109 MHz,
16 tubes (6AG5x2, 7F8, 6SK7, 6SG7, 7H7x2, 6H6x2, 7A4, 6SL7, 6V6x2, 6C4, VR-150, 5U4G);
the successor of the SX-42 All Wave Receiver, no separate band spread dial, horizontal dial

 

Single conversion, IF 455 kHz, 10,7 MHz

Analog dial, separate band spread dial

AM, CW with BFO, FM (above 27 MHz)

Sensitivity
AM: MW 4 uV, SW 0,75 uV

Selectivity 6 dB
13 kHz, 7 kHz, 6 kHz, Crystal filter 1,5 kHz - 50 Hz

RF Gain, Noise limiter,
Crystal phasing Filter

The SX-42 comes in an impressive dark grey metal cabinet, with it's dimensions of 508 x 260 x 406 mm, it weighs 23,6 kg. The SX-42 has a hinged lid cover giving access to the tube sockets as found in most older Hallicrafters sets. The standard SX-42 comes only with a 110 V mains transformer for U.S. use, Hallicrafters offered a multi voltage transformer for international users. You can connect a high impedance speaker to the speaker output sockets, the original matching speaker is Hallicrafter's R - 42.

The front panel is dominated by the big semicircular bright green backlit frequency dial. The main dial is driven by the main tuning knob, it has markings for the broadcast and amateur radio shortwave bands and an additional 0 - 100 logging scale, similar to the one found at the SX-28. The inner concentric part of the tuning knob operates the bandspread dial, this one also with a 0 - 100 scale. A huge rotary knob in the left lower corner of the front panel acts as band range switch, the markings on the edge of the knob are hard to read.

The mains switch / volume control is found just at the right of the main tuning knob, three switches above the headphones jack activate the AVC, the Noise Limiter and the sets the receiver to STANDBY or RECEPTION mode.
At the right, below the round signal strength meter, You find another six rotary controls in two rows.
In the bottom row, You find the SELECTIVITY switch to select one of the three coil or crystal filters. Next is the TONE switch with HIFI and BASS positions for high fidelity performance, and then the SENSITIVITY control, in fact a RF gain control.
In the top row, You find the control for the CRYSTAL PHASING filter, active in the crystal filter positions of the SELECTIVITY switch. In the middle, the RECEPTION mode switch, the position CW activates the BFO, adjust with PITCH CONTROL for zero beat in SSB transmissions or for optimal beat note.
A nice feature for the less technically minded are small red dots indicating the normal setting of all controls for AM reception and green dots for FM reception.

THe RF signal coming from the antenna socket will pass two RF amplifier stages and then be mixed to the intermediate frequency of 455 kHz, in FM modes for the usual 10,7 MHz. After having passed the three coil filters or the crystal filter, the signal is amplified in three IF amplifier stages and handed over to the AM demodulator. A noise limiter mutes the audio signal during short signal peaks. The BFO signal is injected in the demodulator stage for CW and SSB reception. After an audio preamplifier, a push-pull final stage will pass on the audio signal to the speaker connectors, for low impedance speakers, You need a matching transformer integrated in the matching Hallicrafters speaker.

As my SX-42 is misaligned, I cannot give correct informations about the behaviour of an optimally aligned set. In the AM bands, the sensitivity is what You would expect from the single conversion design, selectivity with the LC filters activated is not sufficient to separate two channels with 5 kHz spacing. In CW operation, the crystal filters give good separation and You can "phase out" infering signals with careful use of the CRYSTAL PHASING control.
After a 30 - 60 min. warm-up stability is found good.
The logging scales will help You finding a station later again, but the coarse dial marks are not sufficient to read an unknown stations frequency right from the dial - and remember, the set has not digital frequency display. It has no integrated crystal calibrator, this option is only found in it's successor, the SX-62.
Audio quality in stations without adjacent channel interference is superior, You can enjoy what's coming out of the "high fidelity" final audio stage.

further reading:
d / e: Hallicrafters SX-42 at www.radiomuseum.org
e: the SX - 42 and SX - 62 - two Hallicrafters favourites, John Bryant, James Goodwin, fine tuning proceedings
e: Dachis, Chuck: Radios by Hallicrafters, Schiffer Publishing Ltd, Atglen, PA 19310, USA