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The Grid
QUESTIONS AND ANSWERS
The Grid is a Question and Answer Department maintained especially for the radio amateurs. Full answers will be given wherever possible. In answering questions, those of a like nature will be grouped together and answered by one article. Every effort will be made to keep the answers simple and direct, yet fully self-explanatory. Questions should be addressed to Editor, " The Grid," Radio Broadcast, Garden City, N. Y.
How to Connect Jacks
/ enclose a diagram of a two-stage amplifier. I believe the circuit is correct, but I do not wish to use the amplifier at all times, and so should appreciate your showing me how I can cut out both one stage and the complete amplifier by means of telephone jacks and a plug. Also, please show me how I can do the same thing with the Grimes circuit.
R. U. R., Wilmington, Del.
TO + OF D6T.T BAT.
FIG. I
The circuit submitted to The Grid
will be better understood if their functioning in a circuit, or just what they accomplish, is first made clear. There are only two kinds of jacks that, for the sake of efficiency and reliability, the Grid recommends to its readers. These are the "open circuit" and the "closed circuit" types. The first two jacks in Fig. 2 are of the closed circuit design, while that in the plate circuit of the third tube is an open circuit jack.
The open circuit jack is used to make a simple connection. When the plug is in, whatever instruments are led to the plug, are in series with the wires leading to the jack. When the plug is out, the instruments are disconnected and the circuit is "open."
The closed circuit jack, which is the more used, is employed where it is desired to disconnect automatically one instrument (say an amplifying transformer) while another instrument (telephone receivers for instance) is plugged in its place. Taking jack two, in Fig. 2, as an illustration: When the plug is removed, as it is in the drawing, the outside prongs close down and make contact with the inside prongs. Thus the transformer is in series with the plate circuit of the first amplifying tube, just as it is in Fig. 1. However, when the phones are plugged in, the plug forces the outer prongs farther apart, until they fail to make connection with the inner ones, and, instead, scrape contact with the plug. The phones are now in exactly the same position as was the transformer primary before the plug was inserted.
Whenever it is desired to cut out amplification by plug
THIS problem (if it presents sufficient difficulties to be so termed) like many other radio puzzles is merely a matter of a principle involved, and when this is understood, the solution may be applied to many circuits and uses. Jacks are connected in the Grimes circuit in identically the same manner as they are in a straight amplifier. The majority of broadcast enthusiasts complicate radio circuits, and their resulting radio troubles, by insisting on vast differences between circuits, when fundamentally there exists little or no difference. Almost everything the experimenter may learn through the operation of a Grimes or another receiver, can be applied equally well to experiments with a super-heterodyne, etc.
The arbitrary connections for jacks
TO+OF DET'B" BAT
FIG. 2
The circuit of Fig. 1 with jacks added