July 1938 Radio-Craft
People old and young enjoy waxing nostalgic about and learning some of the history of early electronics.
Radio-Craft was published from 1929 through 1953. All copyrights are hereby acknowledged. See all articles
you do a search for "acoustinator," you get a certain model of acoustic
guitar speaker manufactured by the UK-based company,
Eminence. That, however, is not the same as the "Acoustinator"
developed by Motorola for their "Golden Voice" series of car radios.
It was essentially what we refer today to as a tone control, or
as an equalizer. Not satisfied with creating just one futuristic
sounding techno-term, Motorola also came up with the 'wobbulator'
for use in tuning the receiver IF response. From what I gather in
the Radio Service Data Sheet instructions, a wobbulator is a sweep
frequency generator for testing a filter response shape. In
case there never was a trademark associated with or a current trademark
or trade name assigned to 'wobbulator,' (or alternately 'wobulator')
let it be known that I hereby formally and legally serve notice
of claiming the term. Now if you use it, you'll have to pay me a
Motorola Model 8-80 (Golden Voice) Car-Radio Set Radio Service
Superhet.; pushbutton tuning; spot tuning; "Acoustinator" control;
A.V.C.; Output (max.) 13W.; Battery drain 8.5 (See Data Sheet No.
299 for schematic and other diagrams)
Push-Button Tuner Adjustment
To set the stations, proceed as follows: (1.) Turn the set on
and let it play for not less Than 10 minutes, to assure all electrical
circuits reaching a constant operating temperature. (2.) Select
6 stations to be "set" and arrange the 6 magnets to the approximate
station frequencies as indicated on the scale, locking them in position.
Do not "set" weak stations. (Fig. 1.) (3.) Press the first button.
The motor will bring the mechanism to the first magnet. Loosen the
lock nut. (4.) Tune manually to the exact peak of the station, using
the tuning knob in the control head. (5.) Press the first button
half-way in (far enough to energize the magnet, but not far enough
to start the motor or mute the set.) (6.) Slide the magnet in the
direction of error until a "click" indicates that the latch bar
has engaged in the stop. (7.) Tighten the lock nut. (8.) Proceed
to "set" the other 5 stations.
Spot Tuner Adjustment
(1.) Slip the spot tuner housing up the flexible control shaft
far enough to expose the spot tuner mechanism, which consists of
a small ball bearing, a brass raceway in which it moves, and a slotted
retainer clip which acts as its guide. (2.) Tune in the desired
station as accurately as possible. A tuning meter is recommended,
except for Model 8-40, which has no Acoustinator receptacle. (3.)
With a pair of slip jaw pliers, one jaw of which rests firmly on
the small ball bearing, the other jaw of which rests on the bottom
of the unit, apply enough pressure on the ball to force an indentation
in the brass raceway in which it moves. (Fig. 2.) Proceed to set
other favorite stations in the same manner. The raceway has a double
track. Therefore, should you desire to reset the spot tuner to a
new series of stations, it can be done by moving the ball bearing
over to the second track. To do this, turn the condenser gang to
full mesh (ball bearing at extreme end of raceway) and with a pointed
instrument, force the ball bearing into the adjoining groove. A
third setting can be made only by installing a new raceway. Order
part No. 1X4487.
Plug in the Acoustinator, if the set undergoing alignment is
thus equipped. Set Acoustinator at "Country" and "Voice" positions.
Connect the speaker to the chassis and plug the "A" lead into its
receptacle. Turn the volume control to maximum and leave it in that
position throughout the alignment, reducing the signal generator
output if necessary.
The trimmer labeled 600 kc. in the R.F. coil can must not be
adjusted in the field. It is the key point in the entire R.F. alignment
and was carefully set in the factory by means of an accurate capacity
bridge to its correct capacity (840 mmf.). Before shipment, this
trimmer was covered by a strip of black Scotch Tape, which should
be left in position to eliminate any possibility of shifting its
capacity through error.
(1.) Connect signal generator to control grid of the Osc.-Mod.
tube (6A7 or 6A8G) through a 0.1-mf. condenser, having first removed
the grid cap from the top of the tube. (See Fig. 3.) Connect a 500,000
ohm resistor from the grid of the tube to the grid cap on the lead
just removed from this tube. Turn condenser gang completely out
of mesh. Connect output meter across speaker voice coil. (2.) Set
signal generator at 262 kc. and carefully adjust the trimmers in
the diode coil can to the point showing highest reading on the output
meter. (3.) Adjust the trimmers in the I.F. coil can to the point
showing highest reading on the output meter. (4.) Go over I.F. and
diode adjustment several times to secure maximum accuracy.
Setting the Range
(1.) Connect signal generator to the control grid of the R.F.
tube (78 or 6K7G) through a 0.1-mf. condenser, having first removed
the grip cap from the top of the tube. Connect a 0.5-meg. resistor
from the grid of the tube to the grid cap on the lead just removed
from this tube. (See Fig. 3.) (2.) Set signal generator at 1,560
kc. and, with condenser gang completely out of mesh, adjust for
maximum deflection on the output meter the trimmer in the oscillator
coil can labeled 1,400 kc. (3.) Set signal generator at 535 kc.
Turn condenser plates completely in mesh and adjust for maximum
deflection on output meter, the trimmer in the oscillator coil can
marked 600 kc.
NOTE: The adjustments above set the range so the receiver will
track with the calibrations in the control head.
R.F. And Antenna Alignment
(1.) Connect the signal generator to the antenna lead through
a 0.00015-mf. condenser and to chassis ground. Set signal generator
at 600 kc. and turn condenser gang until signal is heard. Adjust
trimmer on the antenna coil can labeled 600 kc. for maximum deflection
of output meter. (2.) Set signal generator at 1,400 kc. Turn condenser
gang until signal is heard. Adjust for maximum deflection of output
meter, the trimmer in the antenna coil can marked 1,400 kc. (3.)
Adjust for maximum deflection of output meter, the trimmer in the
R.F. coil can marked 1,400 kc. (4.) Recheck steps 1, 2, and 3, for
Use of Oscilloscope in Aligning I.F.'s
Equipment Required: Cathode-ray oscilloscope and a frequency-modulated
signal generator. (Note: if your signal generator is unmodulated,
a frequency modulator will be required to adapt it for use with
(1.) Align I.F. and diode trimmers in the regular manner as outlined
in preceding paragraphs. (2.) Connect "wobbulator" to control-grid
of Osc.-Mod. tube (6A7 or 6A8G) through a a.1-mf. condenser, having
first removed the grid cap from the top of the tube. Connect a 0.5-meg.
resistor from the grid of the tube to the grid cap on the lead just
removed from this tube. (Fig. 3.) (3.) Connect oscilloscope to the
top or high side of the diode load resistor, which, in this case,
is the volume control. (4.) Adjust the "wobbulator" frequency to
262 kc. and observe the picture of the I.F. resonance curve as shown
on the oscilloscope "screen." Correct alignment will result in a
flat top curve, as shown in Fig. 4A. (5.) Should the curve appear
sharp at the "nose" with a shelf on either side of the peak, as
shown in Fig. 4B, adjust the plate trimmer of the I.F. transformer
slightly, until the curve approaches the condition shown in Fig.
4A. If the regular I.F. alignment has been properly carried out,
it will be necessary only in rare instances to adjust other than
the I.F. Plate trimmer.
"X" indicates socket terminals used as dummy tie points.
(Acoustinator, lower-left, is not mounted on set.)
All readings except recto plates are from chassis ground to socket
terminal indicated. Measurements made with 1,000 ohms/volt meter.
Voltage at Battery - 6.3 V. Voltage at Receiver - 6.0 V.
Current Consumption - 8.5 amps. - Output (max.) 13 W.
*Note: The numerals heading the columns refer to socket terminals
(see schematic diagram, Fig. 5).
Automatic Service Notes
Motor Fails to Start
(1.) Motor Contacts in Acoustinator Not Closing. Open the Acoustinator
and inspect the motor contacts. If the gap is too great, contact
will not be made when the button is pressed. Adjust by bending carefully.
(2.) Poor Contact at Acoustinator Plug. Inspect the contacts
between the Acoustinator plug and the receptacle on the chassis.
(3.) Defective Reversing Switch. A defective switch would prevent
the voltage from reaching the motor winding.
(4.) Open-Circuit in Motor. Check all connections to motor and
check motor winding for continuity.
(5.) Motor Brushes Not Making Contact. Check contact between
brushes and commutator.
(6.) Low Battery Voltage. A weak or defective battery in the
car would not deliver sufficient voltage to start the motor.
(7.) Flexible Tuning Shaft Binds. Binding in the flexible tuning
shaft places an additional load on the motor. If this load is too
great, it will prevent the motor from turning the mechanism.
(S.) Magnet Fails to Release. If the magnet which has previously
been energized, fails to release the latch bar for any reason, the
motor cannot turn the mechanism.
Fails to Stop at Magnet
(1.) Open Magnet Winding. Check for continuity and replace if
(2.) Magnet Contact in Acoustinator Not Closing. Open Acoustinator
and inspect contacts. Adjust or clean if necessary.
(3.) Rounded Head On Magnet Core. The head of the magnet should
have sharp corners. Rounded corners may cause the latch bar to slip
going in one direction, although it will usually catch in the reverse
(4.) Latch Bar Defective. Inspect latch bar to make sure that
it has not been damaged. Replace latch bar and gear assembly, if
(5.) Poor Contact at Acoustinator Plug. A poor contact here means
a voltage drop which reduces the pulling power of the magnet.
(6.) Improper Spacing of Latch Bar. Check the spacing between
the latch bar and the magnet. It should be somewhere between 0.01-
and 0.02-inch. If the spacing is greater the pulling power of the
magnet is reduced.
Posted April 28, 2015