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Jacks and How to Use Them
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in radio sets to-day is to change the head set or loud speaker from one stage of amplification to another. To accomplish this efficiently, one or two additional springs are needed on the jack. Figs. 6 and 7 illustrate the schematic connections.
An improvement on the more simple arrangement shown herewith is a connection in which all filaments are extinguished except those that are in actual use. That is, when it is desired to use less than the entire number of stages of amplification only the filaments of the tubes used are connected to the circuit, thus saving both tubes and batteries. To do this complicates the wiring somewhat, especially when there are more than two stages of amplification, but if less than the maximum number of stages are used frequently, the extra complication is well worth while on account of the economy involved. Furthermore, with the more uniform tubes that are now being produced, the tendency is toward the use of fewer filament rheostats, and as the filament rheostat on most sets is the only means of control, the filament control jack is becoming more and more desirable from the standpoint of economy.
Two methods of automatically controlling the filaments are shown in Figs. 8 and 9. ' By following these two circuits out it will be seen that only the filaments of the tubes in use are operated. The circuit shown in Fig. 8 requires jacks with three extra springs for the detector
and for all stages except the last, where two additional springs are needed. The circuit shown in Fig. 9 requires a different type of jack for each position.
At times, it is desired to use the amplifying part of a complete two-stage amplifier, detector, and tuning set with another set in which no amplifier is provided. This is particularly true in the case of very complete amateur stations where a number of different sets are used to get different wavelength ranges. It is desirable in such cases to provide the amplifying set with means to facilitate these connections.
A suitable wiring diagram that provides for great flexibility in this direction is shown in Fig. 10. The terminals marked "External A battery" are for connecting to the A battery terminals of the detector tube set. It is intended that the terminals of the non-amplifying set that are normally connected to the telephone headset shall be connected to a plug and that the plug shall be inserted into the jack marked " External Detector." With the connections shown, the filament control feature is retained and only the tubes in actual use will have their filaments connected to the battery.
It may be well here to say a word to the uninitiated on the use of sets using filament control jacks. The filament of a vacuum tube draws an appreciable amount of current and therefore the voltage drop in all of the filament
FIG. IO
By this arrangement, the signals from any receiver may be amplified by using the amplifying part of this complete receiver. In this case, the tuning elements are automatically cut out and those in the external set are used