October 1954 Popular Electronics
[Table of Contents]
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Popular
Electronics was published from October 1954 through April 1985. All copyrights are hereby acknowledged. See all articles from
in the year 2011, there are still plenty of receivers around that
need to be manually aligned for peak performance. They are not necessarily
all old equipment, either. Super sensitive receivers for radars,
radio astronomy, and security systems are some examples. Of course
there are plenty of amateur radio receivers and vintage AM, FM,
and shortwave radios out there that are still in service by hobbyists
and collectors. Those people probably already know how to tune their
radios, but there are always new people just entering into the realm
that need a helping hand. This article will be a big help to them.
See all articles from
How to Align Receivers
Modern superheterodyne receivers have a number of tuned circuit
adjustments which must be set properly if top performance is to
be obtained. This is as true of small table model receivers as it-is
of large AM-FM-short-wave consoles. The more complex sets simply
have more adjustments and, where FM or TV is provided, may require
slightly different techniques for adjustment. The entire adjustment
procedure, whether applied to a table model receiver or a large
console, is called receiver alignment.
While the beginner
should steer clear of FM and TV sets and the more complex consoles,
there is no reason why he shouldn't undertake the alignment of table
model AM broadcast-band receivers, if he has or can borrow the necessary
test equipment - a multitester (not absolutely essential), an insulated
alignment tool, and an r.f. signal generator.
Fig. 1. Basic receiver adjustments (dotted
boxes) that a layman can make. See text.
adjustments made in a table model receiver during the alignment
procedure are shown within the dotted line boxes in the Simplified
diagram of Fig. 1.
No attempt should be made to align a
receiver unless it performs poorly and preliminary tests indicate
that the set is out of alignment. Alignment is not a magic "cure-all"
that will correct hum, noise, distortion, weak operation, and other
complaints, irrespective of the actual cause.
make the mistake of trying to align sets to correct defects which
they are unable to find because they lack the necessary training
and experience. The fact is, the average receiver seldom requires
realignment unless it has been mistreated.
Here are the symptoms which may indicate the need for alignment:
(1) If the set is weak, but all tubes test good and d.c.
voltages in the receiver are normal (check these against the voltage
values listed in the service manual for the receiver).
If the receiver does not "track" its dial (that is, if the dial
readings do not correspond to the frequency or wavelength values
for the station tuned in) but make sure that it isn't just a case
of the dial pointer slipping.
(3) If the receiver squeals
or oscillates, but tubes are goad and all d.c. voltages seem normal,
and bypass and filter capacitors are in good condition or, if the
oscillation occurs only at one end of the band (generally the low
Above all, take care not to confuse other
tuning circuit troubles with the need for alignment. For example,
a common complaint is that the receiver picks up one station over
the entire tuning range. This is not generally due to misalignment;
rather, it is usually the result of a defective local oscillator,
The operation of a local oscillator may be checked by using
a d.c. voltmeter to check for d.c. voltage across the oscillator
grid resistor (identify the grid pin connection by referring to
a tube manual). If there is a reasonable d.c. voltage here, generally
5 volts or more, the oscillator is probably OK. If not, check plate
and screen grid voltages in this stage and, if these are normal,
try a replacement tube, no matter how the original tube checks in
a tube tester. Make sure the oscillator section of the tuning capacitor
is not shorted (we'll discuss the identification of this section
later) and, as a final step, replace the oscillator coil.
For alignment work you'll need an r.f. signal generator and
an insulated alignment tool, In addition, you'll need an output
indicator of same sort. A d.c. vacuum-tube voltmeter is the preferred
instrument for this job, but you can get by with an ordinary multitester,
or, in a pinch, by using the loudspeaker of the set as an output
indicator. A typical set-up for receiver alignment is shown in Fig.
The output meter may be connected to the receiver in
one of several ways. Three good methods are shown in Fig. 3. If
a d.c. vacuum-tube voltmeter is available, connect its common lead
to chassis ground and the negative d.c. lead to measure receiver
a.v.c. (automatic volume control) voltage, as shown in Fig. 3B.
In many sets". this connection will be to the "hot" side of the
If a multitester is to be used as an output
indicator, set it up for use as an a.c. voltmeter. The meter may
be connected between chassis ground and the plate pin of the audio
output tube through a .5 μfd., 600 volt capacitor, as shown in Fig.
3A. If preferred, the meter may be connected directly across the
loudspeaker voice coil terminals, as shown in Fig. 3C. A typical
connection is shown in Fig. 4.
Fiq. 2. A typical set up for making receiver
alignments as described in the article.
the loudspeaker is to be used as an output indicator, you'll listen
for changes in the loudness of a tone.
The outer shield
of the signal generator lead should be connected to chassis ground
and the "hot" center lead should be connected through a .001 μfd.
paper capacitor (600 volt) to the control grid terminal of the mixer
tube for i.f. transformer alignment. (Identify the proper pin connection
by using a tube manual. Typical mixer tubes are the 6K8, 6A8, 6A7,
6SA7, 6BE6, 12SA7, 12BE6, etc.) For "front end" alignment, the hot
lead of the signal generator may be simply clipped to the loop antenna,
as shown in Fig. 2. No direct electrical connection is made to the
Fig. 3. Three methods of connecting receiver
and the test meter. (A) Meter connected through a capacitor. (B)
With a v.t.v.m. (C) Meter connected across voice coil.
Finally, plug in the test equipment and the receiver, turn
on all units, and allow a few minutes warm-up time before starting
The i.f. transformers are generally located
in rectangular metal cans on top of the receiver chassis, as shown
in Fig. 5. Two adjustments are usually provided in each transformer.
These may both be on the top or .sides of the can, or one may be
on the top and the other on the bottom (below chassis).
Most modern receivers use a two-gang tuning capacitor. Either of
the two types own in Fig. 6 may be used. Trimmer capacitors for
the two sections are frequently mounted on one side of the stator
plates (the stationary plates ... the movable plate section is called
the rotor), but, in some cases, these adjustments may be on the
bottom of the tuning capacitor frame.
Fiq. 4. How a multitester can be connected across the loudspeaker
voice coil terminals.
Fiq. 5. Receiver adjustment points on top of the chassis. See
text for full details.
Fig. 6. Two types of radio tuning capacitors. The one on the
left is found in broadcast-only receivers while the one on the
right will be more often encountered in combination short-wave
and broadcast type sets.
Fiq. 7. Adjusting the local oscillator trimmer.
If the tuning capacitor is like the one shown to the left, the smaller
rotor plates belong to the local oscillator section. If the capacitor
is like the one shown to the right, you'll have to identify the
oscillator and r.f. sections before alignment.
If you are
able to pick up a station with the receiver, bring one finger close
to one set of stator plates, then close to the second set. As you
approach the r.f. stator section, you may find that the signal becomes
weaker, but will not disappear; as you bring your finger close to
the oscillator section, however, the station may disappear entirely,
and you may even find that a different station is picked up.
Should the receiver be so far out of alignment that it is impossible
to tune in a station, you can identify the oscillator section either
by tracing out the circuit or by referring to a service manual.
Referring back to Fig. 1, the i.f. transformer adjustments
correspond to trimmer capacitors C6
. In some receivers, i.f. tuning "slugs" (movable
iron cores) may be used instead of trimmer capacitors. This is usually
the case where adjustments are provided on both the top and the
bottom of the i.f, can.
The r.f. trimmer capacitor (on the
side of the tuning capacitor) corresponds to C3
the local oscillator trimmer capacitor corresponds to C4.
In many receivers, a low-frequency adjustment for the local
oscillator will be provided. This may be either an adjustable local
oscillator coil, using a movable powdered iron core, or a small
"padder" in series with the tuning capacitor (C5
1). Where especially cut plates are employed on the tuning capacitor,
like the one shown to the left in Fig. 6, the chances are that no
low-frequency adjustment is provided. In any case, if a low-frequency
adjustment is available, you should be able to identify it by checking
the connections to the oscillator coil.
With the signal
generator connected to the grid of the mixer tube, as previously
outlined, set the instrument controls to deliver a modulated r.f.
signal at the i.f. value for the set. For most receivers this will
be either 455 or 456 kc. Set the output level controls (the coarse
and fine attenuators) to the minimum signal required to obtain an
indication on the output meter used (or so that a faint tone can
be heard in the loudspeaker, the receiver volume control should
be turned up full. Turn the tuning control of the receiver until
the tuning capacitor plates are full meshed.
Short out the
local oscillator temporarily. Do this by connecting a short piece
of wire between the lug for the stator plates of the local oscillator
section of the tuning capacitor and ground.
Now, using an
insulated screwdriver or alignment tool, adjust the i.f, transformers
for maximum output indication on the output meter (or maximum sound
from the loudspeaker). The proper technique to use is shown in Fig
5. The output meter and signal generator are not shown in this photo.
Go through the adjustment steps at least twice, for the
setting of one i.f. transformer may affect the adjustment of the
The mixer stage and local oscillator are generally
called the "front end" of the receiver. This section is aligned
after the i.f. transformers are properly adjusted.
the outer shield of the signal generator lead still connected to
chassis ground, remove the .001 µfd. capacitor used when adjusting
the i.f. transformers, and clip the "hot" lead to the loop antenna
of the receiver, as shown in Fig. 2. A direct electrical connection
is not usually necessary. Remove the temporary shorting wire used
on the local oscillator in the previous steps.
the signal generator to 1550 or 1600 kc. and tune the receiver to
the same frequency, as indicated by the dial setting. Adjust the
local oscillator trimmer (C4
in Fig. 1) for maximum output.
The proper technique to use is shown in Fig. 7.
signal generator and the receiver tuning to 1400 kc. and adjust
the r.f. trimmer (C3
in Fig. 1) for maximum output.
Finally, if a "padder" (C5
in Fig. 1) or an adjustable
local oscillator coil is provided in the receiver, tune both the
signal generator and the receiver to 600 kc. Make the low-frequency
adjustment (coil or padder) for maximum output while rocking the
tuning capacitor plates back and forth (by adjusting the tuning
knob). Use the adjustment and dial setting that gives maximum output,
irrespective of the actual reading of the receiver dial.
Finally, go back to the high-frequency settings of the signal
generator and receiver and repeat the adjustments of the local oscillator
and r.f. trimmers. You may then wish to repeat the adjustment at
the low-frequency end of the dial, for, if best receiver performance
is to be obtained, the alignment procedure should be carried out
as a back-and-forth process. One adjustment affects the other, so
you have to make slight changes in both to get the best possible
setting of all trimmers.