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An Entirely New Idea in Portable Radio Set Operation

by R.D. Washburne, Radio-Craft, January 1932

Newest among the additions to the growing line of radio devices is a portable radio set designed to operate under widely varying conditions of location and current supply. This is the Radiette Autoverter and Model 30 Troubadour illustrated above, left and right respectively; automotive '36, '37 and '38 tubes are used.
    The receiver chassis is designed as a completely self-contained A.C. set, and is readily put into operation in a hotel room, at home, etc., merely by plugging into a 110 volt A.C. outlet the connection-cord with which the chassis is equipped; one end of this cord has 2-prong plug for the light-line connection, and the other has a 5-prong plug for connection to a receptacle in the chassis. The receiver chassis measures 12 x 15 x 6 inches deep and weighs only 17-1/2 lbs. "Parallel" pentodes are used in the output circuit, which feeds a midget dynamic reproducer

Rear view of the Radiette Model 30 "Troubadour."

    For automotive operation, or wherever the only power supply is a 6-volt storage battery, one additional unit will be required, an "autoverter." This is a mechanism for interrupting a circuit which includes a 6-volt supply and the primary of a special power transformer; the secondary of the latter supplies the necessary high potential which, rectified by the rectifier tube (a type '71A, with grid and plate connected together) in the receiver chassis, supplies the plate potential for the entire receiver chassis.
    When the storage battery is used as the power supply, it is necessary to use a special cable to inter-connect the autoverter and the receiver chassis. The cable has a 5-prong plug on one end, to fit the receptacle in the receiver chassis, and a 5-prong plug on the other to fit into the autoverter. The circuit thus made includes operation of the receiver tube filaments directly from the storage battery.

Principle of Operation

The "Autoverter" showing step-up transformer, filter, and motor-driven interrupter.

This method of obtaining 110 volts from a 6-volt supply was described in the July, 1930 issue of Radio-Craft in the article entitled, "Obtaining 'B' power from a Storage Battery." However, mechanical and electrical improvements have been incorporated in the Autoverter. For instance, a centrifugal switch, which may be clearly seen at the right of the photo above, operates to keep the transformer primary disconnected from the 6-volt supply until the rotating circuit-breaker has gained speed. An electrical refinement is the circuit arrangement which makes it unnecessary to take the filament current through this circuit-breaker and the power transformer. Two remaining units, the R.F. choke and the filter condenser, are shown at the left.
    By a slight modification of the connections it should be quite convenient to operate the Radiette on a current supply of 110 volts D.C. This would call for a limiting resistor (a 110 volt lamp of correct wattage ordinarily is used) which would pass sufficient current to operate the autoverter, just as though it was connected to a storage battery. Naturally, care would have to be taken to prevent grounds--as when the metal chassis touches a radiator--but this method of operation would increase the utility of the Radiette by opening up the big New York, Chicago, and other markets where a great many hotels and homes are equipped with D.C. power lines.

Schematic circuit of the Radiette "Troubadour" chassis. The autoverter consumes 6 A. at 6 V. (battery) and outputs 15 W. at 110 V., A.C. The filaments draw about 2 A.; they connect directly to the battery for D.C. operation and to a 6-volt secondary for A.C.

The Radiette installation may be recommended on several grounds: it is very efficient (tests were conducted by Radio-Craft Laboratories), it presents a fine appearance, it is light in weight, and well constructed, and its components are of high grade. The Troubadour unit, or receiver chassis, is supplied with tubes. (The receiver shipped to Radio-Craft included a type '37 screen-grid detector which became slightly microphonic at high volumes)--the frequency response was exceptionally satisfactory. A pilot light illuminates the recessed, transparent tuning drum.

Installation Data

When the Troubadour chassis is to be operated from a lighting circuit, only the antenna is connected to the receiver. In some instances, however, operation may be a bit noisy unless the chassis is grounded through a fixed condenser of about 0.5-mf. capacity.

The method of installation in a car of course will vary with the individual models. In general, most cars will require some form of interference suppression; a fixed condenser and a kit of special resistors are packed with the Radiette. (The use of these units has been discussed in numerous past issues of Radio-Craft.)

Although the use of supressors will not impair the efficiency of an efficient ignition system, it may be that, in some instances, due to poor condition of the ignition system, unsatisfactory engine performance may result at low speeds. This, of course, should be a warning to repair the ignition system.

The type of car antenna to be employed is a matter which should be settled by an automotive radio technician who is familiar with the signal pickup characteristics of the various makes and models of cars.

The autoverter assembly is mounted in the car by bolts; the holes through which they run are bushed with rubber. The unit must be mounted with the motor shaft horizontal and the oil-cups upward. In case it is not definitely known whether the car battery has a positive or negative post grounded, the polarity should be determined wither by a voltmeter of by inspection of the battery (the larger terminal is usually positive). For best results and long brush life the autoverter should be connected as indicated by the terminals,--red, positive, and green, negative. To these two terminals also are connected a black and a yellow lead; the former grounds to the pressed iron chassis, and the later connects to the grounded battery terminal. If the connections are correct there will be no voltage between the autoverter and the frame of the automobile.
    To compensate for the drain of the Radiette, the battery charging rate should be increased to 18 or 18 amperes.

Service Information

The autoverter portion of the Radiette is fused at 20 amperes. A potential of 270 volts should be read between the chassis and the filament of the rectifier (red lead); and to the "plus 'B'" (blue), 160 volts. Voltages at the respective sockets are as follows:

Plate potential, V1 to V6, 160 volts; screen-grid potential, V1, V2, V3, 90 volts; V5, V6, 160 volts. Cathode potential, V1, V2, V3, 2 volts; V4, 10 volts; V5, V6, 16 volts.


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