July 1932 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
This Radio Service Data Sheet for the Clarion "Replacement"
Chassis, Model AC-160 A.V.C. Superhet is an example of the dozens
of similar schematic and alignment instruction sheets that have
been posted on RF Cafe over the years. Obtaining technical information
on most things, even readily available items, prior to the Internet
era was often very difficult - if not impossible. Service centers
had what was need provided by manufacturers and distributors,
but if you wanted to find a part number or service data on a
refrigerator, radio, lawn mower, garage door opener, etc., and
did not have the original paperwork, you were usually out of
luck. Nowadays a Web search will quite often get you what you
need thanks to people (like me)
who go to the trouble of making the information available. The
stuff doesn't just magically appear or get posted by benevolent
governmental entities. You're welcome.
Clarion "Replacement" Chassis, Model AC-160 A.V.C. Superheterodyne
Radio Service Data Sheet
(Push-Pull Pentodes, Variable-Mu Tubes, Tone Control and
Of the estimated 17 million radio sets now in use in the
United States, the chasses of approximately 11 million are now
obsolete, due to the rapid advance in receiver design. At the
same time, the cabinets in which these chasses are housed are
just as much in vogue as the day they were bought, and they
still represent a considerable portion of the cost of the ensemble.
To offset this discrepancy, a western manufacturer has brought
out a 10-tube super-heterodyne receiver chassis, complete in
every respect, and modern in design, which is to be used as
"replacement" for the older set models. The diagram of this
receiver, the model AC-160, is shown. The chassis is available
The electrical values of the components are as follows: Resistor
R1, volume control, 1,150 ohms; R2, tone control. 0.1-meg.;
R3, 8,000 ohms; R4, 0.1-meg.; R5, 2,000 ohms; R6, 400 ohms;
R7, 0.5-meg.; R8, 40,000 ohms: R9, R12, 10,000 ohms; R10, 30,000
ohms; R11, 0.2-meg.; R13, 300 ohms; R14, 700 ohms: R15, 175
ohms; R16, 2.900 ohms; R17, 4,300 ohms; R18, 3,800 ohms; R19,
R20. 1,000 ohms.
Condensers, C1 , C2, C3, are tuning units; C4, C18, 0.0008-mf.;
C5, C7, 0.02-mf.; C6, C12, C14, C21, C25, 0.1-mf.; C8 0.7-mf.;
C9, C10, C22, 0.05-mf.; C11, 0.00005-mf.; C13, 0.01-mf.; C16,
C23, 8 mf.; C19, C20, 0.35-mf.; C24, 1.0 mf.
Operating-voltage and current characteristics are taken with
the volume control set "full on," and the "supersensitive" switch
turned "to right."
Filament potential PARAGRAPH GRAPHIC HERE PLEASE NOTE ERROR
Do not connect the ground wire to the "Ant." post unless
a fixed condenser is connected in series, to prevent a burnout
of the antenna coil in the event that a ground may have occurred
in the power transformer.
A good ground is important to satisfactory operation: selectivity
and circuit stability depend upon this consideration. The ground
connection is conveniently tested by grounding one side of a
110-volt lamp, noting the brilliancy when each side of the light-line
is connected to the remaining lead of the lamp: a dim light
indicates a poor radio ground. An entire absence of light in
this test usually indicates a lack of ground at the main power
transformer; in this case the local power company should be
Switch SW.2 should not be thrown to the "Phono" position
unless a pickup is in the circuit; otherwise, noise and fluttering
Poor sensitivity may be due to mis-alignment of the tuning
condensers, but the trimmer's of these units should not be adjusted
except as a last resort.
Since this receiver has automatic volume control, poor tone
quality will result if the set is adjusted slightly off-tune.
Therefore, it is recommended that the volume first be reduced
to low audibility, the set tuned for a point mid-way between
the two extreme dial points of reception, and then the volume
brought up to normal.
Another method of checking tone quality at this point is
to substitute for the regular antenna, a very short piece of
wire, so that the volume control must be adjusted to the "full
on" position, when the A.V.C. feature no longer holds, tuning
being "peaked," as in the ordinary types of sets.
A poor tvpe '27 tube used as the second-detector V5, or A.V.C.
V9, will result in poor operation. Note that tubes unsuited
to use in these positions may test "okay" on a tube checker.
In "noisy" localities it may be well to shunt the power line
by a filter system of the usual type - two 0.1-mf. fixed condensers,
connected in series, the two free ends connecting to the two
line-leads, and the center-tap being grounded.
Due to tile high audio gain of this receiver, special precautions
in the design were taken to eliminate hum beyond the normal,
slight degree existing in practically all sets. Consequently,
should a complaint of hum arise. after eliminating the usual
possible causes check the position of A.F. transformer T1. The
angle of its mounting bracket has been carefully calculated
to eliminate hum and if for any reason T1 must be replaced,
be sure to retain the bracket and see that it is not accidentally
twisted out of its original angle.
The tuning condenser nearest the front-panel is C1, followed
by C2, and C3, (in this order); the trimmer for each of these
circuits is located on top of the respective tuning unit. Padding
condenser C4A is located on the front skirt of the chassis,
alongside unit R1-SW.2. Trimmers of the I.F. circuits are located
on the left-hand side of the respective I.F. transformers, the
top adjusting screw of the two being the grid-circuit tuning
control; I.F. transformer I.F.T. 1 is the one nearest the front-panel.
Connect the 175 kc. service oscillator to the control-grid
cap of V2, and to ground. Do not remove any of the tubes from
the sockets; also, it is unnecessary to disconnect the control-grid
cap connection from V2.
After adjusting the I.F. circuit, connect a broadcast-frequency
service oscillator to the input posts of the radio set, and
tune in its signal at 1400 kc. Now adjust the trimmers of C1
and C2, respectively, for maximum output.
To check the calibration of the receiver, whether it is high
or low, the trimmer in shunt to C3 should be adjusted until
a crystal-con trolled station of known high frequency is brought
in, at the correct dial marking, with peaked tuning and maximum
volume. If the broadcast-frequency service oscillator is accurately
calibrated, it might be used in place of the broadcast station's
signal which, however, is held within about 50 cycles by reason
of the crystal-control. In this adjustment a test frequency
of 1400 kc. should be used. Note that at this frequency the
setting of the trimmer of C3 will be exceedingly critical.
Now comes the problem of balancing the oscillator to the R.F.
and detector circuits so that perfect tracking will be obtained
over the entire tuning range.
Tune the external broadcast-frequency test oscillator and
the receiver both to 600 kc., then slowly increase or decrease
the capacity of C4A, at the same time continuously tuning back
and forth across the signal with the receiver tuning condenser
gang. The output meter needle will now be swinging up and down
in step with the variation in tuning. Watch the peak of this
swinging closely and readjust C4A until the swinging needle
reaches its highest peak.
Retune the receiver and broadcast-frequency service oscillator
to 1400 kc. and re-check the trimmer of C3 to make sure that
the adjustment of C4A has not thrown the receiver out of calibration.
Should this have occurred, readjust the trimmer of C3 until
the calibration is correct, and then check on the trimmers of
C2 and C1 to make sure that the adjustment of C4A has not reduced
Schematic circuit, Clarion "Replacement" Chassis, Model AC-160
A.V.C. Superheterodyne. Condenser C17 is 0.05-mf.
Posted September 15, 2015