Radio Broadcast (May 1928-Apr 1929)

our readers suggest Reducing Static A SIMPLE and effective way to reduce heavy static crashes and other interference such as howls from radiating receivers to the signal level has been tried out by the writer on a number of receivers with gratifying results. A neon glow lamp, such as is sold by electrical-supply houses for use as pilot lights on 110-volt lines, is the "magic lamp" which effectively reduces static to ineffectual "plunks," and cuts the ear-splitting howl of radiating receivers to a less offensive squeal that does not rise in volume above that of the incoming signal. The neon glow lamp, known as T14 and rated at watt, costs 60 cents. It has a screw base, containing a resistance compound which prevents excessive current flow when used on standard light circuits. Carefully cut this screw base off with tin snips and remove the resistance compound, being cautious not to break the delicate bulb or the fine lead-in wire. Solder No. 30 copper wires to the leads. Bend a piece of light metal around the glass bulb so as to form a mold for a base. Drop in hot sealing wax or rosin. This will harden into a base which will protect the tube and the delicate terminals. The " static-spill er " is now ready to be connected in shunt with the loud speaker as suggested in Fig. 1. The signal volume shoidd be adjusted to suit the average requirements. At this volume setting the neon tube will not light at all, or only at rare intervals. When static is received if the surge is equal or smaller in amplitude than the incoming signals it will pass through unaffected by the neon tube, but it will be fairly innocuous. The crashing static that makes radio reception impossible is greater in volume than the received signal and therefore "spills over" through the shunting neon tube. When bad static is being received the crashes are visible each time they occur, the tube flashing brightly. When the squeal of a blooper comes through the tube lights, holding the squeal down to the level of the received signal. R. F. Starzl, Le Mars, la. STAFF COMMENT Mr. Starzl's idea should be reasonably effective in many cases. It is not a static eliminator. It is merely a device that has a limiting effect on volume. If the device is set to operate above a certain arbitrary signal level, the effect of any disturbance above this limit will be reduced. It will be desirable to adjust the neon-lamp circuit so that it spills over at the correct To Set Neon Tube Resistor. ^ Lx This department of Radio Broadcast is utilized each month for the presentation of miscellaneous short radio articles which are received from readers. These abbreviated manuscripts describe "kinks," radio short cuts, and economies that the experimenter runs across from time to time and that can be made clear in a concise exposition. Although some of these notes have been submitted by engineers and professional writers, the editors particularly solicit contributions from the average reader. All material accepted, including photographs, will be paid for on publication at our usual rates with extra consideration for particularly meritorious ideas — The Editor. intensity. If it spills over at too low a volume a variable resistor, such as a universal range Clarostat, should be placed in series with it. R.F.Amp. Fig. 1 — A neon tube connected as shown above is an effective static reducer Equivalent Circuit Fig. 2 — The vacuum-tube circuit shown above is an excellent variablerange high resistor A Variable-Range High Resistor THE vacuum tube can be used as a variable high-range resistor for a variety of radio purposes, by taking advantage of the fact that its internal resistance varies with the filament emission. With plate and grid elements of the tube connected together, either filament leg may be used as one terminal of the resistor, and the common grid-plate connection as the other. The filament is controlled by a rheostat, which, in turn, varies the resistance of the plate-filament circuit. Using a 199-type tube a resistance range of from about 3000 ohms to infinity can be secured. The actual lower limit will vary with the voltage applied across the device. The principal advantage of this arrangement is that it provides a silent, velvet variation in resistance. It may be used most successfully as a regeneration or oscillation control in receiving circuits, as suggested in Fig. 2. The use of a 199-type tube is recommended because, in many instances, it will be necessary to use a separate filament-lighting source. The resistor, of course, is operable only in d.c. circuits (such as the plate circuit of a receiver), and the plus side of the line must be connected to the plate-grid terminal. Ralph Van Keuren, Beloit, Michigan. A Good Coil Cement AN EXCELLENT dope for coating solenoid coils, and for giving the necessary rigidity to spiderwebs and other self-supporting coils, may be made by dissolving one ounce of parrafin in one pint of high-test gasoline. This solution may also be used as a substitute for boiling in parrafin in almost any radio impregnation job. S. W. Oldershaw, Waterbury, Conn. Ghostly At Least I HAVE found that my radio set can be enjoyed by everyone in the house by means of a very simple device. I attached a long cord to my loud speaker, and passed it through the same hole that I use to bring my battery wires up from the cellar. Then I place my loud speaker directly in front of the opening where cold air is taken into the hot-air furnace. When I turn on my radio set, the pipes from the furnace serve as carriers, transmitting the music into all rooms of the house. Oftentimes a guest is quite mystified to hear this perfectly transmitted music coming out of the register. Jacque Longaker, Buffalo, N. Y. STAFF COMMENT The idea is novel — useful to an extent, and replete with humorous possibilities. But we should hesitate to second our contributor's characterization of the reproduction as "perfectly transmitted." Hot-air heating pipes hardly have the acoustic properties of an ideal loud speaker. An Economical Voltage Divider THE 2 candle-power 110-volt carbon lamps, purchasable at almost any five and ten cent store for ten cents, make excellent resistor units for radio purposes. Each lamp has a resistance of about 2000 ohms. I have found them particularly applicable to the requirements of a voltage divider in power-supply units. A power source having a maximum potential of 180 volts will require from six to eight lamps for a "bleeder" arrangement. These may be mounted easily by placing them in holes, one inch in diameter, drilled in thin wood or a bakelite strip. After the lamps have been mounted they are connected in series by soldering directly to the screw bases. Employing eight lamps, any voltages between 0 and 180 may be had in 22.5 volt steps. A typical arrangement is suggested in Fig. 3. As usual, each voltage tap should be bypassed to B negative. C. H. Galbraith, Boston, Mass. -| To Rectifier | + 0<5rt>OTC>^TCK> -2 C.P.Lamps ■ O 135 +180 Fig. 3 — A simple inexpensive voltage divider for a B power-supply unit. m march, 1929 page 324 •