Note
The RX-1 was Heath’s first ham band only receiver, and was one of the very first kit-form communications receivers on the market.
The receiver is designed as a companion to the TX-1 “Apache" transmitter, and at first glance the two units are almost indistinguishable from each other. These two rigs were the first Heathkits to wear the famous green colors—a color scheme that became a de facto trademark, and one the company would continue to use more than 20 years.
The RX-1 is typical of equipment designed in the 1950s: it is built on a heavy gauge steel chassis and has a heavy aluminum front panel and a heavy steel enclosure. The operative word here is “heavy.” The RX-1 weighs 52 pounds on the bench. The unit is designed around 15 tubes and will receive upper and lower sideband as well as AM and CW. It covers from 160 through 10 meters (including 11 meters) and has a separate band position (marked “CONV”) and dial markings for 6 and 2 meter coverage with the optional XC-6 and XC-2 converters.
Features include a built-in power supply, 5 switchable selectivity settings, a tunable notch filter, a illuminated S-meter, and a 100 kHz crystal calibrator.
The receiver is a double conversion superheterodyne type with a first IF of 1682 kHz and a second IF of 50 kHz. The front end section, which includes the band switching, RF and HF oscillators, and mixer stages, was pre-assembled, tested, and aligned at the factory. This sub-chassis is simply attached to the main chassis with a few screws and connected by a couple of plug-in cables. The pre-assembled front-end greatly simplified construction and tune-up. In fact, the tune-up can be done with nothing more than the RX-1’s S-meter and crystal calibrator. Other wiring is simplified by a wiring harness.
Sensitivity is better than 1 µV. Selectivity can be adjusted in five steps—5, 3, 2, 1, and 0.5 kHz. The notch filter has a depth of 50 dB. Stability was never specified by Heath, but experientially has been found to be as good or better than most rigs of the genre.
The front panel provides controls for RF, IF and AF gain (with power switch), notch tuning, notch depth, ANL, AVC, BFO, and the band switch. Additionally there are controls for main tuning, calibrator set, calibrator on/off, antenna trimmer, receive/standby, mode, and selectivity. There is also a standard quarter-inch headphone jack on the front panel.
The rear panel has an SO-239 connector for a 50-75Ω antenna and screw terminals for 50-75Ω or 150-300Ω antenna. There are also screw terminals for 8 ohm and 500Ω audio output. Caution: Do not operate the receiver without a speaker or headphones connected.
A rear panel octal accessory socket provides access to B+, 6.3 VAC, AVC, and receiver muting. In addition there is a rear panel switched 120 VAC receptacle and a 1.5 amp cartridge fuse.
The dial mechanism is another of Heath’s gear and pulley assemblies and uses a rotating drum with markings for each band. This drum is illuminated and rotates as the band switch is turned. The drum is plastic and can crack with rough handling. Be sure to check it.
As designed, the RX-1 suffered from a variety of deficiencies. These include poor AGC, distortion of AM and SSB signals, ineffective ANL, an inaccurate S-meter, generally poor audio fidelity, and excessive drift, among others. All of these can be fixed with some effort. Thomas Bonomo, K6AD, has done extensive research into the RX-1 and has published a series in Electric Radio magazine and an online treatise titled Making a Heathkit Mohawk RX-1 Useable. Also see Another Look at the Bonomo Mohawk Mods, a three part series in Electric Radio magazine (see references below), by John Treichler, KJ6SAV.
The unit has a two-tone green front panel with darker green copper clad cabinet. Early RX-1s were shipped with satin finish aluminum knobs, while later versions used polished knobs. In 1963 the RX-1 was replaced by the sleek SB-300—patterned after the Collins S line. Heath continued to sell the RX-1 until supplies ran out early in 1964.
CALIBRATOR OPERATION
The crystal calibrator is activated with a red pushbutton, and a small knob provides fine adjustment of the receiver oscillator. The receiver should be set to a 100 kHz point near the intended operating frequency (7.100, 14.200, 21.300 or 28.500 MHz, for example). Press the red button and use the calibrator control to zero the signal from the calibrator. Caution: On the high bands it is possible to zero the wrong harmonic.
The front end has been pre-aligned with the calibrator capacitor half meshed. Consequently, calibration for any band will be close to this position.
References:
Review. QST. Dec 1958, p. 41.
Review. Radio News, Dec 1958, p. 64.
10 kHz markers for. CQ. Dec 1960, p. 53.
Fuse blowing problems. CQ. Dec 1964, p. 101.
Improvements. 73 Amateur Radio. Oct. 1965, p. 68
Amplified AGC for. QST. Apr 1969, p. 38.
The Bonomo Modifications Pt. 1. Electric Radio Nov 1997.
The Bonomo Modifications Pt. 2. Electric Radio Dec 1997.
The Bonomo Modifications Pt. 3. Electric Radio Jan 1998.
Improved AGC. Electric Radio. Sep 2014.
Another Look at the Bonomo Mohawk Mods Pt 1, Electric Radio. Nov 2017.
Another Look at the Bonomo Mohawk Mods Pt 2, Electric Radio. Dec 2017.
Modifications to the Heathkit RX-1 Mohawk Pt 3, Electric Radio. Jan 2018.
Frequency coverage (MHz): 1.8 to 2.0, 3.5 to 4.0, 7.0 to 7.3, 14.0 to 14.35, 21.0 to 21.45, 26.96 to 27.23, 28.0 to 29.7, 50 to 54 (with XC-6 converter), 144 to 148 (with XC-2 converter)
First IF: 1682 kHZ
Second IF: 50 kHz
Selectivity (switchable): 0.5, 1.0, 2.0, 3.0 and 5.0 kHz
Notch filter: 50 db rejection
Signal to noise ratio: 10 db or less at 1.0 µV
Audio output: 8 or 500 Ω, 2 watts
Power requirements: 120 VAC, 50/60 Hz, 75 watts
Tubes: (1) 0A2, (1) 5V4GA, (1) 6AQ5, (4) 6BA6, (1) 6BJ7, (1) 6BZ6, (3) 6CS6, (3) 12AT7
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
