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Hallicrafters Items

 

Production Year 1960 at $79.95

The Hallicrafters HA-1 T.O. Keyer employs a type of digital circuitry to form perfect code characters and mark ratios at CW sending speeds of between 10 to 65 WPM(Words Per Minute). It was designed by Jim Ricks, W9TO who is now a silent key. Jim was the founder of the high speed CW group known as the Chicken Fat Operators or CFO for short. The 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-1, while the novice operators will discover a whole new command of CW that will lead them to proficiency and unsuspected enjoyment. This keyer operates much in the same way as the old tape transmitter did, both the dash-dot and mark-space ratios remain constant over the speed range. The sending speed and the mark-space adjustments are completely independent of each other.

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. For transmitter keying, the HA-1 employs a silent, mercury wetted contact relay which is perfect for the older tube transmitters. This relay has virtually an unlimited lifespan but does require that the keyer be operated in a position no greater than a 30 degree angle from a horizontal plane. The keyer has complete immunity to line voltage fluctuations and RF(Radio Frequency) pickup. The 3.2 ohm 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 neon light which has two functions; it indicates that power is on and it serves as a visual keying monitor. The light will flash one time for each dit and two times for each dash. The large knob on the left is a four position rotary control knob with the following functions, Power On/Off, Low CW speed setting, Hold(used for tuning), and High CW speed setting. The knob on the right is the CW Speed control and is used in conjunction with the High and Low settings of the knob on the left. Then at the right is a plug for the CW key. The CW key base is connected to the chassis ground and the dot-dash contacts are operated at an extremely low negative potential which makes the CW key assembly completely free from shock hazards.

The rear of the unit has several additional plug sockets and controls. A 1/4 inch Headphone jack is found at the far left. The headphone jack disconnects the internal speaker when headphones are used. The output impedance of the headphone jack is 3.2 ohms, although it can be used with any type of medium or low impedance headphones. Moving to the right, the next control is a knurled shaft for the Sidetone control which adjusts the amplitude of the keyed monitor tone. Then we have a screwdriver slotted shaft for the Balance control which is used to differentially adjust the gain of tube V3 to compensate for tube section differences and general aging. This control is used to set the proper dot and dash ratio when the key lever is pressed. The Balance adjustment should remain fixed for long periods of time and need only be adjusted if service has been performed. At the right is a knurled shaft for the Weight control which sets the time relationship of a dot(or mark) to its following space. For most normal CW operating, this control is usually set for a ratio of 1 to 1. To the right of all of these controls is an 8 pin octal socket that is used to connect the keyer to the transmitter. On the far right edge is the AC power plug and directly above it is the ground connection.   

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 physical dimensions of the HA-1 is 5 5/8 inches high, by 7 inches wide, by 7 13/16 inches deep, and it weighs in at 7 1/2 pounds. The keyer requires a power source of 105 to 125 volts AC at 60 cycles and consumes 25 watts. The power supply consists of a transformer with silicon rectifiers. The photograph on the left is of the front of the keyer, while the right photograph is of the back. In later years the Hallicrafters company produced a transistorized keyer which is the model HA-4.   

These next two photographs show the Hallicrafters HA-1 keyer with the cabinet removed. The photograph on the left displays the tube compliment and some of the other major components that are found on the top of the chassis, while the picture on the right shows the smaller components that are found underneath.

In general, the keyer forms the dots and dashes by the use of digital circuitry and logical sequencing. Both the speed and the mark-space ratios are established by a keyed multi-vibrator that operates continuously as dots and dashes are keyed to form letters. Dashes are formed by adding the output of the time base dot generator with the output from a scale-of-two circuit. Once the dashes are formed, they are always at the correct speed and mark-space ratios. A much more in depth description of the HA-1 circuitry has been detailed below.

The 12AU7A tube(V1) is used as a free running astable multivibrator which is keyed by the series triode portion of tube V2A, which is a 12AU7A tube. The positive feedback from the plate of V1A is fed through resistor R16 which holds V2A conducting after a momentary contact of the CW key has been pressed to produce self-completing dots. The dots are uniform whether momentarily initiated or fully keyed, as in a series of dots. The speed is controlled by a positive grid bias adjustment from the R9 potentiometer. The speed range is determined by the selection of grid return resistors R1 and R6, or R2 and R7. The mark-space ratio is adjusted by a differential grid resistor R8, with no effect upon speed. Tube V3 which is a 12AU7A tube is triggered as a bistable multivibrator, or a scale-of-two circuit. When keyed by the series triode tube V2B(12AU7A), tube V3 may be triggered by a negative pulse formed at the start of a dot from the plate of tube V1B. When it is so triggered, the plate of V3B will flip and remain positive until another negative pulse is received. Operating in this manner, it forms half-speed dots which are added to the output of V1 and drive the relay tube V4A(12AU7A) to form the dashes.

The sidetone signal is produced by a neon-type relaxation audio oscillator which is amplified by V4B, and keyed by the relay. Frequency of the tone is determined by resistor R27 and capacitor C8. The sidetone level is controlled by potentiometer R28. The power supply incorporates an electrostatically shielded transformer to minimize any possible RF pickup and to provide complete isolation from the power line. Silicon rectifiers are used, and tubes V5(OA2) and V6(OB2) provide complete voltage regulation.

With some understanding of the basic circuitry under our belt, lets walk through how the self-completing dot is formed. When the CW key lever closes the contact momentarily to form the dot, the grid bias is removed from tube V2A and it starts to conduct. The multivibrator V1 goes into action and causes the plate portion of V1 which is known as V1A to flip positive which allows the electrons to move through resistor R16 and keep tube V2A conducting to form a self-completing dot. The output from the plate of V1A is now applied through resistor R15 and to the grid of triode V4A which conducts and energizes the relay and a dot is formed.

Now lets walk through how the self-completing dash is formed which is a touch more involved. When the CW key lever closes the contact momentarily to form a dash, tube V2B starts to conducts to "arm" V3 for triggering. At the same instance, diode CR1 conducts to start a self-completing DOT(not dash). Now the same procedure from above begins. The grid bias is removed from tube V2A and it starts to conduct. The multivibrator V1 goes into action and causes the plate portion of VI which is known as V1A to flip positive which allows the electrons to move through resistor R16 and keep tube V2A conducting to form a self-completing dot. The output from the plate of V1A is now applied through resistor R15 and to the grid of triode V4A which conducts and energizes the relay. The leading edge of the negative-going dot from the plate of V1B moves through the differentiator capacitor C3 and resistor R12 to form a negative pulse which triggers tube V3. The plate of tube V3B then flips positive and thus keying tube V1 through diode CR1, until the leading edge of the second dot provides another negative pulse to flip it back negative. The second dot which has already been initiated, goes through completion to end the dash cycle. At which point the plate voltage of tube V1A moves through resistor R15, and the plate voltage of tube V3B moves through resistor R14 to drive the grid of tube V4A positive. When the plate of tube V4A is in a positive state, it conducts and energizes the relay for a self-completing dash.

A couple of final notes on the HA-1 keyer that I would like to discuss has to do with the rating of the mercury-wetted relay contact. The relay is the heart of the keyer so this is an important consideration to keep in mind. The relay contact is rated at 5 amperes maximum, or 500 volts maximum. The product of these two ratings is not to exceed 250 volt amperes, otherwise the contacts on the relay may become damaged. For example, the maximum allowable voltage with a 5 ampere load is 50 volts(5A x 50v = 250 VA). The maximum allowable current with a 500 volt supply is 0.5 ampere(500 V x 0.5 A = 250 VA).

Another consideration is that except for very light loads under 2 MA and 50 volts, the relay must be provided with a contact protection network consisting of a capacitor and a resistor in series. When the keyer is used with most Hallicrafters transmitters and transceivers, no protection network is required.

 

A special thanks to Steve Fitzgerald(N4KQR) who personally hand delivered this item.

  

Resources:

Radios by Hallicrafters with Price Guide by Chuck Dachis

Hallicrafters owners manual  

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