Radio Digest (July 1924-Apr 1925)

Record Details:

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February 7 , 1925 RADIO D I G E S T— Illustrated Broadcast Listener's Reference Library Part I — The Crystal Set with Various Circuits By Edward Thomas Jones, A. I. R. E. THE crystal set will give results, within a radius of twenty-five miles of a powerful broadcasting station which are excelled by no other type of receiver insofar as quality is concerned. A loud speaker cannot be operated directly from the crystal set; however, by adding a two stage amplifier (vacuum tube type) it is possible to operate a loud speaker from nearby powerful transmitters. The most important part of a crystal set is the crystal detector. It is unwise to mount the crystal on the receiving set, it should be mounted on a separate stand so that it will not be jarred out of "ad Figure 1 justment" every time it becomes necessary to change the tuner position. This is especially true of the cat-whisker type of detector. Protection of the Crystal Too much stress cannot be placed on the proper protection of the crystal detector. You must remember that it is not possible (except under very favorable conditions) to receive from great distances with crystal receivers, and what little energy is picked up and made available to operate, the head phones must be taken care of so that reception will be possible. If the detector is not adjusted to its proper state of sensitiveness, the chances are that you will sit and sweat your collar off without hearing a single sound. Therefore, make the proper installation of the detector where it will be safe — and cannot be jarred out of position every time some Figure 2 one sneezes or every time a trolley car passes. This is not far-fetched, but simply covers the situation frankly and makes known facts that every crystal set owner should know. It is the answer to those who have not met with much success with crystal detector sets. WRAPAROUND EITHER AERIAL OR. GROUND WIRE OF RECEIVER. .INSULATED WIRE BUZZER. PUSH BUTTON DRY CELL AD JUSTHENT 5CREWl^_ Figure 3 Next in importance is the selecting of a good crystal. Of course you cannot look at a crystal and tell whether it is a good one or not, although some Radiophans will tell you so. You must try out the crystal and listen in before passing judgment. Why it is Better TUT ASTER of Every Note in the Orchestral Range" is the proven claim of the Federal No. 65 Audio Frequency Transformer! Volume without distortion is the basis for the beauty of Federal Tone. From its oversize locking nuts to its heavy brass mounting feet the Federal No. 65 Transformer incorporates the Boston New York Philadelphia Pittsburgh same engineering skill that has made Federal the recognized leader in electrical communication apparatus since 1890. Insist upon Federal parts for your "pet" hook-up. There are over 130 standard parts bearing the Federal iron-clad performance guarantee. Federal Telephone and Telegraph Go. Buffalo, N. Y. federal " StandardRADIOProducte Chicago San Francisco Bridgehurg Canada Crystals do not cost very much and it will pay you to purchase several specimens, and, after conducting your tests, use the one which gives best response in the headphones. How to Keep Crystal Clean Keep the surface of the crystal clean, especially if the detector is not of the enclosed type. This can be done by making use of an old toothbrush and some gasoline. Simply brush the surface of the crystal with the brush after it has been dipped in gasoline. Do not use soap. When a crystal has been in use for some time it becomes a hard matter to find a very sensitive spot. If, after cleaning the crystal as outlined, the crystal's sensitiveness is not increased, then it will be necessary to take a pen-knife and DETECTOR POTENTIOMETER. , DRY CELL Figure 4 scrape the surface of the crystal. An experimenter at one time suggested that the mineral be ground down by properly applying it to the face of a carborundum stone. To the writer's knowledge, quite a number of experimenters have been successful in restoring crystals in this way. Always be sure to connect the ground post to the tuner lever or swich. If this is not done, and you bring your hand to rest on the metal parts of the switch while tuning, you ground the signals through your body and decreased signal strength results. This is shown in figure 2. Since it is not possible to pick up signals without the detector in adjustment, then the only way to operate a crystal receiver is to provide a local sending sta tion which will permit the adjusting of the detector. Purchase from any electrical house a small "watch case" high frequency buzzer, CARBORUNDUM Figure 5 two dry cells, a small push button and sufficient wire to make the connections. Proper connections are shown in figure 3. Note that an extra wire is run from the contact post of the buzzer to either the aerial or ground connection of the receiver. Whenever you press the button the buzzer sends out minute electrical waves. If the detector is adjusted, you Figure 6 will hear a high pitched buzz in the head phones. By readjusting the detector you may find a "spot" where the "buzz" will come in louder — the crystal is then adjusted and you may then divert your attention to the tuning in of the broadcast (Continued on page 26) Si' pffm m WilMI v> r 3oo,ooo Tungars already in use / The new Tungar charges both radio A and B batteries, and auto batteries, too. Two ampere size (East of the Rockies) $18 The Tungar is also available in five ampere size (East of the Rockies) $28 10 cycles — 110 volts The new Tungar does all the old Tungar did — and more. It will charge both radio A and B batteries, with no change except slipping the wire from one terminal to another. It charges 2, 4 or 6 volt A batteries — 24 to 96 volt B batteries — and auto batteries, too. It is simpler than ever to use. Just two clips and a plug. No need to disconnect your battery from your set, or make any change in the wiring. The Tungar charges overnight while you sleep. And it makes no disturbing noise. It is more compact than ever. It has a new bulb, unchanged in principle, but more convenient in size and use. G-E research has made a good product better! Keep your batteries charged with a Tungar — and get the most out of radio. Tu nga r REG. U. S. «B^^ PAT. OFF. I BATTERY "cHARG ER| Tungar— a registered trademark — is found only on the genuine. Look for it on the name plate. Merchandise Department General Electric Company, Bridgeport, Conn. GENERAL ELECTRIC