Hallicrafters SX-42 Operating Instructions
Excerpted from SX-42 Owner's Manual, Copyright 1946 Hallicrafters Co.
The Model SX-42 is a 15 tube superheterodyne radio receiver designed to
provide amplitude modulated (a-m) reception over the frequency range 540 kc (kilocycles)
to 110 mc (megacycles) and high fidelity, frequency modulated (f-m) reception over the
frequency range 27 to 110 mc. Calibrated bandspread is provided for the 80, 40, 20, 10,
and 6 meter amateur bands. The general coverage dial and bandspread dial are operated from
one tuning control which consists of two independent knobs turning on concentric shafts. A
dial lock is provided to lock the unused dial while tuning the receiver. This exclusive
Hallicrafters feature insures accurate tuning and logging.
||Type of reception
Adequate overlap is provided at ends of all bands. The receiver as normally supplied is
designed to operate from a 105 to 125 volts 50/60 cycle, single phase source of a-c power.
These operating instructions also cover Universal Models which operate from a 105 to 250
volts, 25/60 cycle single phase a-c source.
2. AC OPERATION
Be sure line voltage is 105 to 125 volts and frequency is 50 to 60
cycles before inserting power cord plug into power outlet. Be sure all tubes are securely
inserted in their proper sockets before receiver power is turned on. The chart below lists
the current and voltage data.
During a-c operation, the shorting plug supplied with the receiver must
be in the octal socket on the rear apron of the chassis.
3. D-C OPERATION
The receiver may be operated from a 6 volt d-c source, generally a
storage battery, and a 270 volt d-c supply in the form of "B" batteries or
vibrator type power pack. Consult the chart on power requirements at the end of this
paragraph and provide battery or power pack facilities capable of supplying these demands.
The receiver is connected to the--d-c supply as follows:
1. Remove the octal shorting plug for a-c operation from the socket SO-1 located on the
rear apron of the receiver chassis.
2. Wire an octal plug, as shown in Fig. 10, and plug it into socket SO-l. Use #19 (AWG)
wire leads for the 270 volt "B" supply connections to pins #3 and #5, and #'12
(AWG) wire leads for the 6 volt battery connections to pins #1, #7, and #8. CAUTION:
Check the wiring carefully before connecting to the battery supply. The chart below lists
the current voltage data.
Total battery drain when operating from a 6-volt vibrator power supply
is approximately 16 amperes.
4. OUTPUT CONNECTIONS
Output connections for the speaker are provided for on the rear apron of the chassis.
Two output impedances are available. Either the 500/600 or the 5000 ohm speaker connection
may be used according to the output impedance desired. This arrangement of dual output
impedances will accommodate most requirements. The Hallicrafters Model PM-23 speaker
requires 5000 ohms impedance; the Hallicrafters Model R-42, R-44, R-75, or R-80 requires
500/600 ohms. However, any standard type, permanent magnet dynamic speaker with output
transformer may be connected to the output terminals. If the permanent magnet dynamic
speaker impedance is unknown, try the 5000 ohm and then the 500/600 ohm impedance, and use
the one which gives the better tone quality and: volume.
5. PHONO INPUT CONNECTION
A receptacle is provided on the rear apron of the chassis for connecting a phonograph
record player to the receiver. This receptacle is designed to accommodate a Cinch, type
M-93, pin connector plug.
6. ANTENNA AND GROUND CONNECTIONS
The Model SX-42 is designed for a 300 ohm antenna impedance. The
antenna impedance is not critical and excellent reception can be obtained from an antenna
of from 50 to 600 ohm impedance. For maximum performance, the best possible antenna should
The antenna terminals on the Model SX-42 are arranged for any type of
antenna from those requiring a ground to those using a transmission line. The transmission
type of antenna connects to the A-1 and A-2 terminals whereas a single wire antenna
utilizes terminal A-1 for the antenna lead. A-2 and GND terminals must be connected
together and connected to a good ground.
7. DETAILED OPERATIONS
a. Controls and Their Functions. In order to obtain the desired
results from the receiver, it is recommended that you become familiar with the function of
each control, Red indicators on the controls for broadcast reception and green for f-m
reception are there to simplify operation. Controls and their functions are as follows:
(1) BAND SELECTOR. The BAND SELECTOR knob
operates the bandswitch to select the desired band of frequencies. The frequency range
covered by each band is read directly on the BAND SELECTOR knob.
(2) General Coverage Tuning and Bandspread Tuning Control.
The larger of the two concentric knobs tunes the receiver to the desired frequency.
The smaller knob provides bandspread action or fine tuning as indicated on the bandspread
scale. The winged knob in the center alternately locks the general coverage and the
bandspread dials so that one remains fixed while the other one is being tuned. The knob
should be rotated in a clockwise direction only, locking first one dial and then the other
as it is turned through one complete revolution. Note that the locked dial knob is free to
turn, but that the dial itself is locked in position.
(a) General Coverage Dial. The general coverage dial has six
calibrated scales and a logging scale. All six scales are calibrated in mc. The calibrated
metal skirt of the general coverage dial knob acts as the vernier calibration for the
logging scale. The outer logging scale (on the general coverage dial) isdivided into 21
divisions, each division representing one revolution of the vernier dial which also
carries a logging scale divided into 100 divisions, thus providing 2100 divisions for
logging use. The dial settings for the various amateur bands are indicated on the main
tuning dial by black dots and the abbreviations 80M, 40M, etc. directly below the dot.
When tuning the amateur bands with the calibrated bandspread dial, the general coverage
dial must be set and locked at the setting corresponding to the amateur band desired.
For a reference when tuning in foreign broadcast stations, the word
FOREIGN has been placed at the appropriate positions along the dial scales. The f-m
channel 88 to 108 mc has been divided into 100 divisions by the scale above it marked 0,
10, 20, 30, etc. in green numbers which correspond with the frequency modulated channel
assignments. Since the general coverage and bandspread tuning systems are electrically
related, it is necessary to set the bandspread dial at "0" when tuning
the receiver with the genera1 coverage dial control to obtain correct receiver frequency
readings on the general coverage dial.
(b) Bandspread Dial. The bandspread dial has
five scales calibrated for the amateur bands and a 100 division logging scale. The five
scales are calibrated to read receiver frequency directly in mc when the general coverage
dial has been set to the corresponding indexing dot and locked in position.
(3) AVC-OFF Switch. This switch when set at AVC,
provides a relatively constant volume level at the speaker for reasonable variations in
signal strength at the antenna by automatically controlling the sensitivity of the
receiver. Best results are obtained when the SENSITIVITY control is set at maximum
sensitivity. The AVC switch MUST be set at OFF for c-w code reception.
(4) NOISE-LIMITER-ON Switch. This switch
opens or closes the noise limiter circuit and is to be set at ON when the operator wishes
to limit excessive noise resulting from automobile ignition and other forms of noise
The noise limiter circuit "clips" the intermittent noise
peaks down to the level of the desired signal where they tend to become unnoticeable.
(5) RECEIVER-STANDBY Switch. When set at
STANDBY, this switch renders the receiver inoperative, while transmitting or for any other
purpose, although the tube heaters remain hot and ready for instant use.
(6) CRYSTAL PHASING Control. This control
permits the discrimination of code signals whose frequencies are very nearly the same. The
SELECTIVITY control must be set at one of its three crystal selectivity positions when
using the phasing control.
It is extremely simple to attain single signal c-w reception with the
SX-42. First. set the RECEPTION switch at CW and the SELECTIVITY control at CRYSTAL SHARP.
Pick a good solid c-w signal, preferably a commercial station because a commercial is
likely to stay on long enough for you to complete the phasing adjustment for single signal
You will find on tuning across this signal that it has two amplitudes.
Tune first to the weaker of these two amplitudes. Next, turn the CRYSTAL PHASING control
until the weaker of the two amplitudes is reduced to a minimum. Then, tune to the stronger
of the two amplitudes and adjust the PITCH control to a tone most pleasing to you. This
adjustment for single signal selectivity will hold with no further adjustment unless you
change the phasing control.
(7) SELECTIVITY Control. This control
determines the sharpness of the response. Six degrees of selectivity are provided, ranging
from CRYSTAL SHARP for c-w code reception under difficult receiving conditions to NORMAL
BROAD response for high fidelity reception.
1. BROAD I-F (for high fidelity reception)
2. MEDium I-F (more selectivity, less bass)
3. SHARP I-F (reduces adjacent channel interferences and gives less highs)
4. CRYSTAL BROAD (similar to sharp i-f but sharper cutting on sidebands)
5. CRYSTAL MEDIUM (greatly increased sideband cutting very little highs present)
6. CRYSTAL SHARP (position of extreme selectivity - practically no sideband content)
(8) TONE Control. This control selects the tone
qualities desired by the operator. The four types of response available are LOW, MED, HI
FI, and BASS.
(a) LOW. The bass and high audio frequencies are
attenuated to provide a minimum response for voice reception when the background noise
level is objectionably high.
(b) MED. The bass and high frequencies are attenuated somewhat less than
for the LOW position providing a response for more than the ordinary voice
frequencies. This position is preferred for voice communication when the signal to noise
ratio will permit.
(c) HI FI (High Fidelity). The bass and high
frequencies are passed at the same level as the mid-frequency range thereby providing as
near a true reproduction of the original signal as possible. The response is essentially
flat between 50 and 15,000 cycles per second for high fidelity reception.
(d) BASS. The response in the high frequency end
of the audio range remains uniform as for the HI FI position; however, the level of the
lower frequencies is boosted above the level of the medium and high frequency ranges.
(9) CW PITCH Control. This control varies the
frequency of the beat frequency oscillator thus varying the pitch of the c-w code signal
(10) SENSITIVITY Control. This control adjusts
the sensitivity by varying the resistance in the cathodes of the r-f and i-f amplifiers.
Turning the control to the right increases the sensitivity. This control must be set at
maximum sensitivity when using the carrier level meter. At any other setting of this
control, readings of the carrier meter are meaningless.
8. "S" METER ADJUSTMENT
Adjustment of the "S" meter control is performed by varying
the knurled knob located on the rear apron of the receiver chassis. This control enables
you to properly set the "S" meter to zero. In order to make the adjustment
correctly, advance the SENSITIVITY control to 10 (red dot). Set the AVC switch at ON
position. Short the two antenna terminals to the ground terminal and tune receiver off
station. Then adjust the "S" meter control until the pointer rests on left hand
zero. Remove the short from the antenna terminals and the meter will indicate the relative
carrier strength of each incoming signal as various signals are tuned in.