Fun with your Broadcast Radio Set

(continued)

The dolls, which are made of celluloid, are very light. Their feet are tipped, each with the blunt end of a common pin. The secret of the successful operation is that these pins must be aligned very carefully; for, if one is even a trifle short, the dolls will not dance.

The source of their motion is found in the vibration of the diaphragm in response to the second frequencies. The dolls, slightly jarred by the vibratory impulses, move to and fro most realistically, in exact time with the music.

“Home Broadcasting”

• STILL another phase of radio enjoyment is the use of a microphone with the amplifier in the radio set, for home “public address.” A microphone is a very useful source of entertainment at house parties, where mock auditions and programs are something new and different for the guests and a boon to the host or hostess looking for new sources of interest for their guests. It is specially interesting, because few people know the sound of their own voices.

Attaching the microphone, a microphone transformer, a small battery, and some wire, to a receiver will permit the enthusiast to use the amplifier in his radio to “broadcast” his own programs which is interesting for house parties, etc., as mentioned before. Parts designed specifically for the purpose are made by several manufacturers and can be purchased from many radio stores and supply houses, at very low prices.

The connections are quite simple. Fig. 6 shows how the parts are wired. The unit can be enclosed in a small box with terminals for the microphone and for connecting the unit to the set. One of the latter terminals is connected to the ground and the other to the grid of the “first audio tube.”

The contact to this tube can be made by removing it from its socket and twisting the wire around the grid prong. To be more explicit, first determine which tube is the one in question, by referring to the instruction booklet accompanying the set, or by asking your dealer; and then remove it from its socket. If it is a tube of the '27 type with five prongs, the grid prong is the one with wider spacing than the others. This (shown at the right of Fig. 4) represents the base of the tube looking up from the bottom. If the tube is of the '01A or other four-prong type, the grid prong is as shown at the left.

The other connection to the set is made to the ground terminal; this completes the circuit through the grid of the tube. By this method, the microphone transformer is connected, across the regular audio transformer in the set. However, it has been found that the results are practically the same, whether the latter transformer is left in the circuit or not, if the detector tube is removed from its socket'while the microphone is being used. The instruction booklet will also tell which is the detector.

There are many other uses than the one described for this unit, that will suggest themselves to the experimenter. As the full amplification of the set is available, the arrangement may be employed for club meetings and other gatherings of people; mother can use it to call “Willie” when he is too far away for her voice to carry, etc. With a good microphone and transformer, the quality can be made equal to the quality of broadcast reception.

Radio-Phonograph Duet

• MANY sets have a pair of terminals for connecting a phonograph pick-up, for reproducing records through the receiver. For a set not equipped with this convenience, adapters can be obtained to connect one of these units.

A very novel scheme was suggested some time ago, for playing the radio and the phonograph simultaneously, with a record as the source of music. Anyone having a phonograph and a radio can perform this stunt without difficulty, and it is very amusing.

Fig. 7 shows the turntable of the phonograph with the usual tone-arm in place on the record. In addition, the electrical pick-up is mounted exactly opposite. When the record starts to rotate, music will be heard coming from the phonograph as well as from the radio. The music from the two sources will be slightly out of time, because the two needles are not at the same point on the record; even though they are placed in the same groove.

This produces the effect of an echo and may be made to increase the “realism” of the music, by careful adjustment of the two needle positions. When they are set the right distance apart on the record, it appears as if one instrument is accompanying the other; and, of course, a still further displacement causes the two to conflict with each other.

It will be found quite intriguing for the fan who appreciates the new large phonograph records, with their operas and classical concerts; as it permits him to adjust the tone of the music to suit his taste, and makes use of the greater quality and volume furnished by the radio set amplifier and speaker.

End

The article following was taken from POPULAR SCIENCE MONTHLY for February, 1917

An Airtight Quenched Spark-Gap

Whether or not qucnched spark-gaps should be made completely airtight has often been a subject of dispute. The Telefunken gaps are usually fitted with plain mica separating-rings, and no great pains are taken to exclude air from the space between the sparking surfaces. In spite of this, the Telefunken transmitters as a rule operate efficiently and with uniform, clear spark-tones. The effectiveness with which a quenched-gap prevents “backfiring” depends to a large extent upon the condition of the parallel sparking-surfaces. If these are perfectly smooth and very slightly oxidized, the operation of the apparatus is usually most satisfactory. How long the plates will remain in good condition depends upon the material from which the sparking-surfaces are made, and also upon the freedom with which air is admitted to the gap. Copper plates which are not provided with airtight gaskets soon become so thickly covered with oxides or compounds including nitrogen that gap action grows irregular; it is therefore desirable to exclude air from such instruments. When silver surfaces are used, the oxidization is not so rapid, and it is not necessary to take such precautions.

The drawing, which is taken from 1916 patent No. 1,171,598, issued to L. DeForest, shows a method which has been found very useful for making quenched-gaps airtight. The structure comprises the usual plates 4, piled upon each other and clamped by means of screw 16 into containing frame 13. Electrical connection is made through the wires 18 which are connected to the clamping-heads 15. The novelty claimed for the present patent consists in the use, between the individual plates of the quenched-gap, of washers consisting of soft compressible varnished or impregnated fabric. When this material is clamped between the plates it effectually prevents the entrance of air, and so limits the formation of oxides upon the surfaces of the plates. Further airtightness may be secured by filling the space between the peripheral rims of the plates with a compound such as paraffin or beeswax, as shown at 10.

In building quenched-gaps of airtight construction, care must be taken that the normal cooling of the gap is not greatly reduced by prevention of ventilation. Also, in using compressible gaskets, the screw 16 must be carefully adjusted in order that the plates be not forced into accidental contact. If the necessary precautions are taken to insure permanence of separation of the plates, an airtight gap is likely to require cleaning much less frequently than one in which oxidization is permitted to progress freely.

Such an airtight quenched spark gap is especially useful on ships at sea and at any land stations which would be effected by the rapid action of salt air upon the material of the gap where it is heated by the spark.

In such a case a gap of this type will not only work more efficiently but will wear considerably longer.