Hallicrafters HA-1, Operating And Service Instructions

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3-4-3. GROUNDING POST
The ground post, provided at the rear of the keyer, should be utilized to
establish a ground for this unit.
IMPORTANT
It is recommended that the unit permanently connected to the
station grounding system so as to prevent the possibility of a
shock hazard developing as a result of component failure.
3-5. RELAY CONTACT PROTECTION NETWORK
Except for very light loads (under 2 mA and 50 V), the relay must be
provided with a contact protection network consisting of a capacitor and resistor
in series. This network is shown in the lower right-hand corner of the chassis in
figure 4. The network prevents possible arcing which would eventually destroy
the contacts. The voltage and current requirements of the circuit to be keyed
should be determined, and the relay contacts provided with an appropriate
protection network prior to the connection into the circuit.
The chart (figure 5) affords a convenient means of determining the necessary
contact protection.
Hallicrafters Model HT-30, HT-32, HT-32A, HT-32B, HT-37, HT-44, SR-150
and SR-160 Transmitters require no protection network when used with this
keyer.
For the most effective protection, the network, as determined from the chart,
should be installed as close to the relay contacts as is possible. It is desirable to
install the network internally, directly at the relay socket; however, adequate
protection will be provided by installing the network at the network at the control
outlet.
To determine the proper protection network required for loads exceeding 2
mA or 50 volts, proceed as follows:
(1) Measure load current of circuit to be keyed with a suitable ammeter.
(2) Measure open circuit load voltage at the keying points.
(3) To find C, read directly up from the value of load current on the
horizontal scale to its intersection with the sloping capacity line; the
value of C is determined from the right hand scale.
To find R, read directly up from the load current value to its
intersection with the appropriate load voltage line; the value of R is
read from the left-hand scale.