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How to Build a Two-Stage Radio-Frequency Amplifier
RADIO-FREQUENCY TRANSFORMER DESIGN
THE style of winding of a radio-frequency coupler offers an interesting field for study. Spiderweb and diamond weave styles have lately come to the forefront of radio design because of the mechanical and electrical advantage they present and the ease with which they may be made and mounted. The same value of inductance can be provided in a concentrated spiderweb or diamond weave form which, if constructed as an ordinary single-layer coil would require a much larger space. Also, with these new inductances, the distributed capacity of the coil has been materially lowered which increases the overall efficiency of the unit. When the winding is concentrated, the magnetic field set up by the currents travelling through the coil is similarly concentrated and does not feed over into adjacent coil units.
Engineers have made electrostatic coupling a special study. Full reports of their findings are not yet available. However, the few bare facts such as separation of parts, concentration of coil winding, and simplicity of wiring serve to guide us toward correct constructional design. The circuit of the radio-frequency amplifier described here is shown in Fig. 5. This amplifier may be used with any type of detector and audio-frequency amplifier now available. In a future number of Radio Broadcast we shall describe a detector and
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amplifier unit especially designed for use with this radio-frequency amplifier.
This circuit consists of three tuned circuits. The output of the last circuit connects to the input of the detector tube to be used. The antenna and ground are connected to the primary of the first circuit.
As may be seen by the several photographs accompanying this article, all the parts are mounted upon the panel and a baseboard is eliminated. As far as possible, the ideas brought out in this discussion have been incorporated in the amplifier unit described here.
CONSTRUCTION OF THE UNIT
TO MAKE the amplifier in accordance with these instructions, it is well to procure the parts as listed. Other parts of similar design and quality may he used with equally good results. The use of uv-201-A or dv-2 tubes is recommended but others such as if and 3 volt tubes may be satisfactorily employed.
The coils used were made up by the F. W. Sickles Co. of Springfield, Mass., from specifications supplied. For those who wish to wind their own, the coil data is included in the following pages.
THE PANEL
TN LOCATING the holes to be drilled in the * panel, it is well to lay off the dimensions on the rear of the panel. Otherwise the
6 V. A 45 V. B 45 V. B
FIG. 5
The schematic circuit diagram of the amplifier whose construction is described. The heavy line indicates the brass bus bar strip connections