Production Year 1961 $59.95 The Hallicrafters HA-4 T.T.O. keyer employs digital circuitry to form perfect code characters and mark-space ratios at CW sending speeds of between 8 and 50 WPM(Words Per Minute). The HA-4 employs 8 transistors and 10 diodes in its construction.and it is often referred to as the transistorized version of the Hallicrafters HA-1. The HA-4 keyer is packed with features that many operators will come to admire. The experienced CW operators will greatly appreciate the stability and precision of operation of the HA-4, while the novice operators will discover a whole new command of CW that will lead them to proficiency and unsuspected enjoyment. Some of the features of the keyer include a pleasant sounding sidetone signal generator with volume control. This feature is useful for practice, instruction and for the monitoring of CW signals. Any type of CW paddle is suitable for use with this keyer. The loudspeaker faces out towards the front of the unit and is of the permanent magnet moving coil design. Sounds exit through a perforated section on the front of the unit. The entire keyer is housed in a sturdy metal cabinet. The front panel layout is as follows, on the left is a CW speed control knob, followed by a Volume control knob in the middle, and on the right is a four position rotary control knob with the following functions, Power On/Off, Auto, Semi, and a Hold position that is used for tuning. The rear of the unit has several additional connections and controls. At the left is a 3 terminal strip that is used to connect the keyer to the transmitter. On this strip, the screw terminal at the right is used to ground the keyer to the transmitter. The 3 terminal strip in the center of the back panel is the CW paddle connection. The screw terminal at the left is for dashes, the one in the center is for the ground, while the one at the right is for the dots. Located at the right on the rear panel is two operator controls. The control on the left is a screwdriver slotted shaft for the Weight control which sets the time relationship of a dot(or mark) to its following space. Then at the far right is a switch to select between the High and Low settings. The physical dimensions of the HA-4 is 2 1/2 inches high, by 7 1/2 inches wide, by 5 13/16 inches deep. The keyer requires a power source of 125 volts AC at 50 to 60 cycles and consumes 1.5 watts. The mark-space terminology that is used above refers to the relative duration of the dot and space. This is known as the mark-space ratio and is usually adjusted for a 1 to 1 match. A dash is formed by bridging the space between two dots. The spaces between the dots and dashes in a letter are uniform. A standard word is equivalent to 24 dots and spaces. A speed of 10 WPM is therefore 240 dots per minute, or 4 dots per second. The photograph on the left is of the front of the keyer, while the right photograph is of the back. The keyer that is featured on this web page is in the same condition as it was received. As can be seen in the above picture of the back of the unit, a former owner has added some type of identification number to the back panel. This is not the serial number of the unit, but rather a number so that a former owner or the authorities could identify should the item become lost or stolen. | 
