Note
The HR-20 and HX-20 are matching rigs designed primarily for mobile use and represent a general refinement of the MR-1 Comanche and the MT-1 Cheyenne, which they replaced.
The HR-20 receiver is an SSB/CW 8-tube design covering 80-10 meters. No PC boards are used—all wiring is point to point. It uses a hermetically sealed crystal filter and has a 3000 kHz first IF. Sensitivity was advertised as better than 1.0 µV on all bands. Selectivity is 3 kHz at 6 dB down, 10 kHz at 60 dB down. It can be used as a mobile or fixed-station radio with the appropriate power supply.
The HR-20 is stabilized with extensive temperature compensation, plate voltage regulation using an OA2, and regulation of the filament voltage of the RF amp and mixer/oscillator with a transistor/zener diode combination.
A product detector is used for SSB and CW signals. The BFO is crystal controlled and provides for USB and LSB tuning. Features include lighted dial and meter windows, a built-in series ANL, front panel selection of fast and slow AVC action, and outputs for an 8Ω speaker and 500Ω headphones. There is no built-in speaker.
Front panel controls include USB/LSB selector, RF gain, AF gain/power on/off, noise limiter, AVC selector, main tuning, band switch, antenna trimmer, and SSB-CW-AM selector.
Rear panel connections include an SO-239 for a 50Ω antenna and connectors for operating and control voltages, antenna relay, speaker, and headphones.
The dial mechanism has a 30:1 tuning ratio and incorporates a rotating drum. The drum is fragile and may crack easily. The condition of this drum (and the integrity of the band switching mechanism) should be checked by rotating the band switch through all positions. The band switching mechanism is a complicated scheme of springs, gears, and pulleys; beware. Note that the matching HX-20 transmitter does not use a rotating drum. The HR-20 is fitted with polished metal knobs and has a light green front panel with dark green cabinet.
Note: The HR-20 can be used only in vehicles with negative ground. There is no internal power supply. The rig must be used with either the MP-1, HP-10 or HP-13 series (for mobile use) or the UT-1, HP-20, or HP-23 series (for 120 VAC use).
References:
Review. 73 Amateur Radio. Dec 1962, p. 36.
Review. QST. Mar 1964, p. 58.
Improvements. 73 Amateur Radio. Mar 1966, p. 74.
Dial pointer improvement. QST. Jun 1966, p. 74.
Frequency coverage: 80, 40, 20, 15 and 10 meters
IF: 3.0 MHz
IF crystal filter:
mid-frequency: 3000 kHz
bandwidth @ – 6 db: 3.0 kHz
bandwidth @ –60 db: 10.0 kHz
Sensitivity: 1.0 µV or better, at least 10 db signal-to-noise ratio
Power requirements:
filaments: 12 volts @ 2.5 amps, and 6 volts @ 5 amps, AC or DC
high voltage: 275 to 350 VDC @ 85 to 125 mA,
total power: 63.5 watts
Tubes: I (2) 6BZ6, (2) 6EA8, (1) 6BE6, (1) 6BJ7, (1) 6EB8, (1) 0A2
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
