Note
In the fall of 1976, Heath announced two new products: the HR-1680 receiver, and a companion transmitter, the HX-1675 transmitter, which, the ad said, would be “coming soon." Both were designed to be fully solid-state replacements for the venerable but aging tube-type DX-60B and HR-10B novice pair.
Heath had no trouble getting the 1680 receiver working and delivered on schedule, but the 1675 transmitter gave engineers a lot of headaches, mostly related to the driver and final amplifier transistors, which burned up frequently—often for no discernible reason. Adding to engineers' frustration was the distraction of Heath’s problem-plagued HW-2026.
It turned out that “coming soon” was almost two years. It wasn’t until the summer of 1979 that the transmitter was finally released, by which time it had been redesigned to use tubes in the driver and final amplifier, and renamed to HX-1681.
The HX-1681 is a CW only transmitter covering 500 kHz segments of the 80-15 meter bands and the 28.0 to 28.5 MHz segment of the 10 meter band. There are no provisions for WARC band coverage. It is not fully solid state. It uses a 12BY7 driver and a pair of 6146s in the final amp. Power output is rated at 100 watts minimum on 80-15 and 75 watts minimum on 10.
Features include full break-in CW (QSK), a built-in VFO, solid state T/R switching, and an adjustable sidetone level. As in the matching receiver, the transmitter is built around several plug-in PC boards. The card edge connectors on these boards are subject to oxidation over time and may need periodic cleaning.
Front panel controls include sidetone level, CW level, band switch, tuning, meter function switch, and mode switch. A bias adjust control is located on the right side of the chassis, behind the cabinet shell. HFO and VFO level adjustments are located inside.
Rear panel connections include an SO-239 antenna connector, an 11-pin power connector and RCA jacks for a 50Ω receiver antenna, receiver muting, amplifier keying and sidetone. A “linear” mode is provided for use with an external amp. In this mode, the receiver is muted continuously during transmit with a selectable amount of delay time being chosen by the operator.
The original units had a lot of trouble with key clicks. Eventually, Heath offered a free modification to owners and incorporated the fix into new units. An excellent modification to solve the key click problem is described in the March 1981 issue of QST magazine.
Note: The HX-1681 requires an external power supply such as the HP-23 series.
The HX-1861 was a good rig but was not as successful as its companion receiver and was pulled from production a year earlier than the HR-1680. It would probably have been more popular had it been fully solid state and included an internal power supply.
Oddly, connecting the HX-1861 with its HR-1680 companion receiver requires a small modification of the receiver in order to mitigate sidetone overloading and distortion. See HR-1680 for details.
Light green front panel with red plastic dial window (illuminated) and a dark green cabinet.
POWER CONNECTOR PINOUTS
Pin 1 — –130 V Pin 7 — GND
Pin 2 — Filament common Pin 8 — NC
Pin 3 — +250 V Pin 9 — Power switch
Pin 4 — +800 V Pin 10 — Power switch
Pin 5 — GND Pin 11 — NC
Pin 6 — 12.6 V filament
References:
Review. QST. Mar 1981, p. 48.
Review (more on). QST. Apr 1981 p. 53.
Alignment. QST. Dec 1985, p. 50.
RF output power (nominal): 100 watts, 80 to 15 meters, 75 watts on 10 meters
Output impedance: 50Ω, less than 2:1 SWR
Frequency coverage (MHz): 3.5 to 4.0, 7.0 to 7.5, 14.0 to 14.5, 21.0 to 21.5, 28.0 to 28.5
Dial accuracy: with 2 kHz after calibration to the nearest 100 kHz marker
Tuning backlash: 50 Hz or less
Tuning rate: approximately 15 kHz to revolution
Harmonic radiation: at least 50 db down at rated power output
Spurious radiation: at least 60 db down at rated power output
Mode of operation: CW only
Keying: break-in with automatic antenna switching an muting of HR-1680
Power requirements:
700-850 VDC at 250 ma (1.0% ripple max)
250 VDC at 50 ma (0.05% ripple max)
–130 VDC at 10 ma (0.5% ripple max)
12.6 volts AC or DC at 2.5 amps
Tubes: (1) 12BY7, (2) 6146A
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
