Note
The HD-10 was Heath’s first keyer and the first keyer kit on the market. It sold well but used a relatively complicated mechanism. It lacked adjustability once assembled, had a poor dot/dash weighting scheme, will not accommodate iambic keying.
The basic problem is this: The keyer uses a pair of microswitches on either side of the paddle arm. Moving the paddle back and forth clicks the switches and operates the appropriate keying circuits. While the spacing between the switches can be adjusted, the switches themselves are not adjustable and have a minimum travel distance required to operate correctly. The result is excessive paddle travel. Enough that operation above about 15 words per minute (WPM) becomes problematic. A workaround would be to connect an external paddle.
The HD-10 employs a pair of microswitches on either side of the paddle arm. Moving the paddle back and forth clicks the switches and operates the appropriate keying circuits. The unit uses 11 socketed transistors and has a built-in transformer operated solid-state power supply.
It features a built-in sidetone speaker and has controls for sidetone volume, speed, and weighting. There is also a “hold” switch for tuning.
During assembly, the builder could choose one of two speed ranges—10 to 20 WPM or 15 to 60 WPM. Changing the speed range involves changing the value of two resistors (R13 and R22) on the main circuit board. Both are 10kΩ for high range, 68kΩ for low range.
The keyer can be configured in a variety of ways: normal or reversed right or left hand operation, or semiautomatic operation, and for use with a straight key or external paddles.It can also be battery powered. Reverse operation requires rewiring of the paddle switches. Dots and dashes are self-completing.
The HD-10 is for use only with transmitters using grid-block keying. Keying output: keyed line to ground. Polarity: negative to ground only. Maximum open circuit or spike voltage: 105 volts. Key-closed current: 35 ma maximum. Connections on rear panel include the keyed line, receiver audio, 45 volts battery input, 22.5 volts battery input, and external key/paddle input.
The unit is finished in two-tone green wrinkle paint. Replaced by the HD-1410 in 1975.
Caution: Do not exceed keying voltage and current parameters as defined in the specifications below.
Setting Dot-Space Ratio with a VTVM
( ) Set speed control to the 9 o’clock position
( ) Connect the DC test leads from the VTVM between the GND and KEYED LINE screws of the 8-screw terminal board. Set the VTVM to the +15 volt range. A meter reading of approximately 3 volts should be obtained with the paddle in the neutral position.
( ) Hold the key in the DOT position. The meter should read about 50% of the previous reading. If not, hold the SPEED control and adjust the screwdriver adjust control for the proper meter reading. It may be necessary to place some object against the paddle to keep it in the DOT position while making this adjustment.
References:
Review. 73 Amateur Radio. Mar. 1966, p. 50
Review. QST. Jan 1967, p. 45.
Improved performance. QST. Feb 1968, p. 56.
Protecting transistor switch. QST. Feb 1968, p. 58.
Use with external paddle. QST. Sep 1968, p. 51.
Protecting from RF. QST. Jun 1969, p. 50.
Better paddle action / cathode keying. QST. Aug 1969, p. 34.
QSK mod for SB-series. CQ. Jan 1971, p. 18.
Speaker change. QST. Aug 1972, p. 52.
Modification. QST. Feb 1974, p. 41.
Positive key line. QST. Jul 1978, p. 34.
Squeeze paddle. QST. Aug 1978, p. 31.
Positive lead keying. Ham Radio. Nov 1978, p. 88.
Use with solid state rigs. QST. Apr 1983, p. 38.
Speed: 10 to 20 WPM, or 15 to 60 WPM
Keying output: keyed line to ground
Voltage polarity: negative to ground only
Maximum open circuit of spike voltage: 105 volts
Key-closed voltage: 0.2 volts, maximum
Key-closed current: 35 mA, maximum
Audio: internal speker or high impedance headphones
Power requirements: 120 VAC, 50/60 Hz
Battery power: 45 volts with 22.5 volt tap (or two 22.5 volt batteries), 14 mA
Solid State: (7) 2N407, (3) 2N2712, (1) 2N398A
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
