Note
The HX-10 was Heath’s first self-contained sideband transmitter and was not a replacement for the TX-1 Apache—the two rigs were sold side by side for about three years.
The HX-10 uses 21 tubes and 9 diodes and covers 80 through 10 meters. It runs 180 watts input on CW and FSK, 180 watts PEP on SSB (upper or lower), and about 75 watts input on AM using a pair of 6146 tubes in the PA cage.
Features include filter-type SSB operation, a multi-section, hermetically sealed band-pass filter, a dual conversion crystal-controlled heterodyne oscillator, ALC, and a fan-cooled final amp. In addition the operator can choose manual, PTT, or VOX control (VOX was built in). The HX-10 also features VOX controlled break-in CW operation and a built-in sidetone for monitoring CW transmission.
To improve stability, VFO plate and screen voltages are regulated and the filaments in the VFO remain lighted, even when the main power is off.
The main tuning mechanism is a worm gear type assembly featuring spring-loaded gears to minimize backlash. The dial uses a heavy flywheel and has a 165:1 turning ratio yielding about 10 kHz per revolution. Like all tuning linkages of this kind, repair may be complicated.
There is a provision for one crystal-controlled frequency. Crystals used are in the 4900 to 5500 kHz range and any given crystal will produce 7 frequencies—one for each band. See crystal formula calculations below.
All power supplies are built-in, and the bias supply is solid-state.
There is a plastic cover window protecting the illuminated slide-rule dial, but it is sometimes found to be missing in units picked up at flea markets. Care must be taken not to damage the dial markings or the pointer.
Every control needed for normal operation is available on the front panel. These controls include the mode switch, audio gain, driver tune, band selector, main tuning (note that the main tuning knob has a 0-100 scale on it), frequency control (VFO or XTAL), drive level, spot level, meter function, final load, final tune, and controls for VOX operation. The front panel also has a mic connector and a key jack.
There is a control on the rear apron of the HX-10 for adjustment of the scope monitor level. Rear panel connectors include an SO-239 for a 50-75Ω antenna, an RCA jack for spotting signal output, an RCA jack for phone patch input, a quarter inch jack for FSK keyboard input, a 120 VAC power receptacle (switched, 200 watts maximum), a ground post, and an octal accessory socket. This socket provides connections for receiver muting, external amplifier cutoff bias, connections to receiver audio, and power for a 120 VAC external relay. There is also a RCA jack for monitoring the RF with an oscilloscope.
Two-tone green finish with polished chrome knobs. This was the last rig Heath made in the “big/heavy” style.
CRYSTAL FREQUENCY CALCULATIONS
To find the crystal frequency, subtract desired operating frequency from the heterodyne mixing frequency for the correct band:
80 meters – subtract 9.0 MHz
40 meters – subtract 12.4 MHz
20 meters – subtract 19.4 MHz
15 meters – subtract 26.4 MHz
10A – subtract 33.4 MHz
10B – subtract 34.0 MHz
10C – subtract 34.6 MHz
Crystal frequencies can be tweaked with the trimmer (C129) on the VFO enclosure.
References:
Review. QST. Oct 1962, p. 55.
Normal grid current. CQ. Sep 1962, p. 68.
FSK for. CQ. May 1963, p. 71.
Key click filter. CQ. May 1963, p. 94.
Transceive with SB-300/301. QST. May 1973, p. 30.
Spurious radiation from misaligned traps. QST. May 1980, p. 41.
Restoring. Electric Radio. Sep 2007.
Emission types: CW, AM, USB, LSB, FSK
Power input: 180 watts CW, and FSK; 180 watts PEP SSB; 75 watts AM
Power output: 100 watts nominal into 50Ω, CW, FSK, SSB; 25 watts AM
Output impedance: 50 to 75Ω with not more than approximately 2:1 SWR
Frequency range:
3.5 to 4.2 MHz
6.9 to 7.5 MHz
13.9 TO 14.5 MHz
20.9 to 21.5 MHz
27.9 to 28.5 MHz
28.5 to 29.1 MHz
29.1 to 29.7 MHz
Frequency stability: 100 Hz after warmup
Tuning knob ratio: approximately 10 kHz per turn
Carrier suppression: 50 db below peak output
Unwanted sideband suppression: 55 db below peak output
Keying: grid block for full break-in CW provided by operating VOX from keyed tone
Audio input: high impedance microphone or phone patch
Audio frequency response: 400 to 3000 Hz ±3 db
ALC: control voltage applied to IF amplifier stage
Power requirements: 120 VAC, 50/60 Hz
off: 4 watts
standby: 200 watts
key down: 400 watts
Tubes: (1) 5U4GB, (1) 6AU6, (2) 12AT7, (1) 12AU7, (1) 6AL5, (3) 0B3, (1) 0A2, (1) 6CL6, (3) 6CB6, (2) 6146, (1) 5R4GY, (1) 6AW8, (3) 6EA8
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
