July 1933 Radio-Craft[Table of Contents]
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 from Radio-Craft.
This Radio Service Data Sheet for the Motovox Models 10A All-Electric and 10E Battery-Operated "Moto-Tetradynes" 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.
The model 10A car-radio set is a superheterodyne; the model 10E receiver is a T.R.F. set incorporating a manual sensitivity control; both instruments include A.V.C.)
Latest in the car-radio line of receivers developed by Motormeter Gauge & Equipment Corp. are the Motovox All-Electric model 10A, and the Battery-Operated model 10E.
The model 10A 5·tube set installation includes the following items: chassis, remote tuning control, reproducer and harness, antenna lead-in, filter bypass condensers, suppressors "B" unit and harness; a superheterodyne circuit is utilized.
The model 10E 5-tube receiver includes the following equipment: chassis, remote tuning control, reproducer and harness, antenna lead-in, filter bypass condensers, suppressors; a T.R.F. circuit is used.
*Measured to ground·; **to cathode. Readings taken with a 1,000-ohms-per-volt meter; "no signal" setting of set. Total drain, 31 ma.
*Measured to ground; **measured to cathode. Use a high-resistance meter. Drain, 19 ma.
Sensitivity of models 10A and 10E, 3/4-microvolt-per-meter; power output, 2.25 w.
Since the intensity of signal strength delivered by the antenna to the receiver is directly proportional to the height and effective length and inversely proportional to the resistance of the antenna, it is necessary to use every precaution to obtain an effective auto-radio antenna installation. Thus, only a low-capacity shielded lead-in should be used; also, the antenna should not come closer than 3 ins. to any metal-work. A counterpoise antenna is used in an automobile since no actual ground is available. The height of the antenna is, therefore, equal to the distance between the flat plane of the antenna and the body of the car. Consequently, the most efficient aerial is one in which the capacity of lead-in and aerial matches the antenna stage of the receiver, covers the largest possible area and is as far removed as possible from the body of the car.
The following instructions pertain to the installation of the model 10A set. After mounting the power supply, run the separately shielded red lead, in the reproducer, to terminal No.3. Next, connect the red lead in the radio cable to the "B+" terminal in the supply and the yellow lead to the "B-" terminal, making certain that the shield of the cable is anchored by the mounting clamp provided in the power supply. Now connect the black, yellow-tracer lead of the tuning control along with the yellow lead from the power supply terminal No. 2 to the ungrounded or "hot" post of the battery. Connect the black lead from terminal No. 1 of the power supply to the grounded battery post. Make certain that the connecting to the battery are correct. Do not pull forward the switch underneath the tuning control until the receiver has been plugged into the harness, otherwise, the power unit win be operating without a load.
Installation instructions which apply to the model 10E receiver are as follows. Connect the yellow lead in the "B" harness to the negative tap of the 180 V. battery (four Burgess type 2308 batteries). Next, connect the maroon lead to the"+45" tap, and the red lead to the "+180" tap. In this line is a 1/4-A. fuse.
The sensitivity control on the model 10E set is located in the bottom of the receiver. After tuning the set to a no-signal position near 1,400 kc., turn the sensitivity control right, or clockwise, to "stop," then back it, counterclockwise, until the static level becomes very high. This is the point of maximum sensitivity. to exceed this will result in lack of sensitivity and A.V.C. It is recommended that this control be set just below maximum sensitivity to reduce engine interference.
Due to the current interest in automotive radio installations the following information concerning car antennas is furnished through courtesy of Motometer Gauge & Equipment Co. Although most of the late car models are equipped at the factory with an aerial of some type, earlier cars will usually require the services of a technician acquainted both with the technique of handling car upholstery and the demands of good antenna design.
It is recommended that No. 14 or No. 16 mesh copper or galvanized screen be used. Do not forget to clear the dome-light by 3 ins. In fastening the lead-in to the screen, a No. 18 insulated wire should be used and if the aerial is copper screen it should be soldered around two adjacent sides so that a good electrical connection is assured. The screen should then be securely tacked at all points possible, making certain that it is not grounded to any metal part of the top. Conceal the lead-in and replace the top, soldering the end of the No. 18 wire to the short shielded lead-in which is provided with most sets, making sure to insulate the soldered joint well; ground the shield to some part of the metal body. Keep the unshielded portion of the lead-in, that is, the No. 18 rubber covered wire, as short as possible so that the shielded lead-in actually enters, if possible, the metal corner post. eliminating the possibility of spark pick-up by the unshielded lead.
Top construction may be divided into the following general classifications:
Open and Convertible. Loosen the top slightly preliminary to putting it back and weave a No. 18 insulated wire around the border between the top and the flap, giving in all a total length of about 60 ft. of wire. Then bring down the lead-in in the manner described above, and re-tighten the top.
Screen Wire Tops. Clip a 3 in. border around the top. Lace the center screen to the edges, using raw-hide,
Standard Fabric Tops. This type of top will be found most frequently. Use a wire screen, as described, removing it 3 ins. from all metals.
Radio Service Data Sheets
These schematics, tuning instructions, and other data are reproduced from my collection of vintage radio and electronics magazines. As back in the era, similar schematic and service info was available for purchase from sources such as SAMS Photofacts, but these printings were a no-cost bonus for readers.
Posted August 7, 2015