June 1936 Radio-Craft
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
These 8 new schematics from a 1936 issue
of Radio-Craft magazine for vintage tube-type car radios brings the total to 210
posted on RF Cafe. Included are Motorola "Golden Voice" Model, RCA Victor Model H-6, Simplex Model TA, Automatic "Magic Eye" Model A1, Arvin Model 28, Philco Model 818, Fada Model 266 Motoset, Bosch Models 736, 737, 738.
The Motorla "golden Voice" model features a "magic eliminode" circuit which not only
filters out automobile engine noise, but balances the noise out of the antenna lead, so that suppressorless
operation is possible on almost all cars. A glance at the schematic shows that all that
magic is performed by a built-in L-C filter network for the power supply, and an antenna
tuning circuit. In those days, installation of a radio in a car usually required the
skills of an electronics technician in order to match the antenna and fine-tune the
receiver according to its environment.
Diagrams of the Newest Car-Radio Receivers
The friend of design of the new receivers can most readily by an examination of the actual
(1) Automatic "Magic Eye" Model A1.
A novelty of this set is its "magic eye" 6E5 tuning tube. The set may be had with or without
this feature. Operation is possible in most cases with only a generator condenser and a distributor
suppressor. The set is mounted directly below the dash, and no remote control is used. Alignment
of the set is done at 1,400 kc. Installation is made with 2 screws fastened to the dash and
a single heavy bolt at the rear, through the motor compartment bulkhead. For installation
in the Willys 77, a roof antenna of about 10 square ft. of copper screen should be used. Voltages:
Plate - V1, V2, 220; V3, 120; V4, 200. S.-G. - V1, V2, 95; V4, 220. Cath. - V1, 3; V2, 3.7;
V3, 1.3. Bias of V4, 14 V., drop across the "B" choke. (Photo on page. 712)
(2) Bosch Models 736, 737, 738. These
sets are the same except for the speaker equipment. The model 736 uses a self-contained speaker,
model, 737 is used with a header-type speaker, and 738 has a separately mounted dash speaker.
Various makes of cars will require different treatment for noise suppression, but complete
instructions are furnished with the set. The tubes used in this set are quick-heater types.
The tone control knob is located on the side of the receiver case. The antenna cable is cut
to a specific length and should not be shortened. Any excess may be coiled up out of the way.
An antenna loading is included in this cable. This set may be used with any type of car antenna.
The new grid-bias cell is used in this receiver and under normal use will not need replacement
during the life of the car. The 0Z4 rectifier tube is similar in action to the old BH rectifiers,
but is much improved. Voltages to be found in this set will vary rather widely according to
the condition of the battery and vibrator, but the normal high voltage is around 240 V. A
20 A. fuse is used forprotection of battery. (Photo on page 712)
(3) Simplex Model TA. This is one
of comparatively few using the synchronous type of vibrator, which eliminates the necessity
for a rectifier tube. If the car battery is grounded on the negative side, the vibrator must
he removed from its socket and tuned half-way around before inserting. It is normally shipped
for use with the ground on the positive side. An antenna trimmer is used to adjust the set
to the most accurate balance with the, particular antenna used. The trimmer is located at
the bottom of the cabinet under a small plug. It should be adjusted with. the set in the car,
and connected to the car antenna. Ordinarily, only a distributor suppressor is necessary with
this car, the battery input being well filtered.
(4) Fada Model 266 Motoset. This
set may be used with a self-contained speaker, a roof or other outside speaker, or it may
be used with dual speakers. The plug connections of the different types are shown at the bottom
of the diagram at right. The input "A" leads are very completely filtered, to keep out ignition
noise. The antenna input transformer is of the iron-core type, and this unit raises the sensitivity
of the set to a considerable degree. Two of the new metal tubes are used, including the 6Q7
double-diode triode, which is closely equivalent to the 75. Voltages at tube prongs are: Plate
- V1, 162; V2, 160; V3, 162; V4, 107; V5, 226. S.-G. - V1, 68; V2, 66; V5, 236. Plate current:
V1, 3; V2, 3.4; V3, 2.9; V4, 0.3; V5, 19; V6, (total) 37. These readings were taken with a
1,000 ohm-per-volt meter and are not indicative of effective voltages. The readings were taken
with a supply voltage, of 6.0, and the current was 5.6 A. The I.F. transformers are to be
aligned at 175 kc., while the gang trimmers are set at a reading of 1,500 kc. The oscillator
aeries trimmer must be aligned at a frequency of 600 kc. The "hot A" lead has a fused connector
for protection. (This is the circuit of the receiver shown at upper right, page 713.)
(5) Philco Model 818. When this set
is used in a car having a lop antenna, under-car antenna, spare-wheel antenna, or any other
having low relative capacity (50 mmf. to 450 mmf.), use connector plug in "A." For antennas
of high relative capacity, such as metal insert top antenna, insulated door, insulated trunk
cover (450 to 2,500 mmr.), use condenser plug in "B." Adjustment frequencies are: 1,550 kc.
and 580 kc., for R.F. and detector. The antenna adjustment should preferably be made with
the set in the car and attached to the car antenna. Iron-core I.F. transformers are used and
add greatly to the sensitivity of the receiver. All leads out of the receiver case are very
completely filtered. Continuously variable tone compensation is available. The input lead
from battery is fused. The manufacturers prefer not to give complete voltage data, since voltages
vary widely with different conditions, but with a fully-charged battery, the high voltage
is about 180 to 220 V. (Photo on page 712.)
6) RCA Victor Model H-6. A special
antenna circuit is used which contains a band-pass filter, affecting a sharp reduction of
frequencies out of the band of 540 to 1,660 kc. "Hot" spots of ignition interference on the
chassis have been carefully located and grounded. A single-position tone control is used.
There is a total of 7 tuned circuits in the R.F. section of the set. The reproducer is a separate
unit. Alignment frequencies are: 1,400 kc. for ant. and det. coils, and 600 and 1,400 kc.
for osc. coil. Undistorted output is 1.75 W. and maximum is 3.5 W. Battery current drain is
6.55 A. A control panel mounts directly in the dash of the car. Set size is 6 1/8 x 9 5/8
x 6 1/2 ins. high. Voltages : Plate - V1, 205; V2†, 205; V3, 205; V4, 90*; V5, 235.
S.-G. - V1, 82; V2, 82; V3, 82; V4, 20*; V5, 245. Cath. - V1, 2.5; V2, 2.5; V3, 3; V4, 0;
V5, 20. *Cannot be meas. with ordinary meter. †V2, osc. plate, 205.
(7) Motorola "Golden Voice" Model.
This set contains the "magic eliminode" circuit. which not only filters out motor noise, but
balances the noise out of the antenna lead, so that suppressorless operation is possible on
almost all cars. This unit also incorporates
an antenna tuning circuit to properly match and tune the set to any type of antenna. Besides
the tone control and the normal volume control, this set has a variable sensitivity control,
which is mounted on the front of the case. The input tuning coil of the R.F. stage is of the
iron-core type. The output stage is of the class AB type, with a separate bias rectifier system,
using a 6H6 with an independent filter. The bias from this source is used on both A.F. stages.
The circuit herewith published is the latest and supersedes all others. Delayed A. V.C. is
employed and is affected by the use of V4 in conjunction with V5. Do not connect any condenser
from the hot "A" lead to ground as this would nullify the action of the eliminode. All necessary
filtering is contained in the latter. Current drain from a fresh battery is 8A., producing
250 V. (Photo on page 712.)
(8) Arvin Model 28. This set may
be had with either enclosed or separate speaker. Also matching dash control panels may be
had, or the set may be equipped with a streamline steering-column control. A complete noise
filter is built-in. Special iron-core antenna tuning system consists of two couplers assuring
high gain on the smallest antenna. Full A.V.C. holds signal steady, while continuously-variable
tone control covers complete tonal range. The set must be balanced at 1,400 kc., and checked
for accuracy at 1,000 and 600 kc. Tubular fixed condensers are firmly fastened to chassis,
eliminating broken leads. Copper plated chassis and case with locking snap-on covers add to
stability and ease of servicing. Only one hole to drill to install chassis in any position,
back or side. Tuning condenser is rubber mounted and has an improved high-ratio vernier drive,
enabling the greatest possible ease of tuning. Voltages: Plate - V1, V2, V3, 235; V4, 120;
V5, 230. S.-G. - V1, V2, V3, 90; V5, 235. Cath. - V1, V2, 4; V3, 2.3; V4, 1.6; V5, 16. Osc.
plate, V2, 160.
Posted August 3, 2017