Radio mirror (Jan-Oct 1923)

RADIO DIGEST ILLUSTRATED How to Prevent Howling in a Set Condenser in the Grid and Filament Circuit All that is needed to make the tryout Is a .001 fixed condenser — a phone condenser of the right size will do. Attach leads to each end of the condenser and WORKSHOP KINKS? EARN A DOLLAR— THERE are many little kinks worked out at home that would aid your fellow Radio worker if he only knew about them. There are new hook-ups, new ways of making parts and various unique ways of operating sets that are discovered every day. Radio Digest is very much interested in securing such material. Send them in with full details, including stamped envelope so rejected copy may be returned. The work must be entirely original, not copied. RADIO KINKS DEPARTMENT, Radio Digest Illustrated, 123 West Madison St., Chicago, 111. HOOK-UP THAT REDUCES NOISE TICKLER. ■^ZZZ/l VOLTS 40 VOLTS 40 VOLTS connect one wire to the post marked "grid" on the amplifying transformer of the second step, the other to the negative of the tube socket of the first tube. A mica condenser is best for this purpose. Make sure the condenser has been tested and is not shorted. If more than two tubes are used, follow the same method. The diagram shows the connections. — Joe McCormack, Godsden, Alabama. Non-inductive Potentiometer The illustration shows a non-inductive potentiometer or rheostat which -can be made cheaply. The materials needed are «fi I SLIDER. SLIOER.ROO PENCIL LEAD BASE one slider, one rod, four Fahnestock clips and the lead out of an ordinary lead pencil. The Fahnestock clips serve as binding posts and holders for the lead by fastening two of them at each end of the lead and passing a wood screw through the holes in their ends and into the base. When both pairs are fastened on in this manner the lead is passed through the two under the rod and connections are made to the other two. When used as a potentiometer leads are taken off at both ends of the lead and at the slider rod. Connections are made at the slider rod and at one end of the lead when used as a rheostat. — Earl Litt, Cherryvale, Kansas. Aerial Construction One pound of No. 14 copper wire generally provides the correct span for the receiving antenna which picks up the broadcasting stations operating on 360 and 400 meter wave lengths. In comparison with this the aerial of the powerful navy Radio station at Annapolis, Md., consists of 10 miles of wire, weighing approximately seven tons. The great mass of wire is held aloft by six 600foot steel towers. The natural p«riod — that is the wave length of the aerial alone — is 4700 meters. The station operates on a wave length of 17,145 meters. Heavy accumulations of ice on the wires would cause great strain and break many A. B. C. LESSONS (Continued from page 11) maximum brilliancy. First adjust the switch S until the antenna circuit is tuned to the desired wave length. Next turn the rotor of the coupler until the desired degree of coupling is obtained between the antenna circuit and the closed oscillation circuit. Finally the set is thrown into resonance by adjusting the variable condenser C-l. The filament rheostat is another important factor to consider in tuning the set, for as stated before, the filament temperature as well as the plate potential must be of the correct value to secure most effective operation of the tube. Consequently, if the signals cannot be brought in very clear or loud by manipulation of the coupler and condenser, try adjusting the filament rheostat, and generally this will be found to do the trick. In fact, at times the rheostat adjustment is so critical that a vernier attachment is necessary in order to bring the tube into the proper operating condition. By a vernier attachment is meant merely an auxiliary resistance adjustment capable of making very fine changes in the current flow or filament temperature. Sometimes improved results can also be obtained by altering the plate potential a few volts. If it seems as though the tube were not functioning at its best, change the B battery contact from the 22% -volt tap to the 21 or 19%-volt tap, or even as low as the 18-volt tap. This will often bring about surprising results. Important Points to Remember In order that a receiving set can operate at maximum efficiency, the resistance of the interior circuits should be as low as possible. Therefore all interior wiring should be done with copper wire at least No. 18 in size, although No. 14 or 16 is better. All contacts should be well soldered so as to insure perfect electrical contact. It is a good idea to cover all wire with insulation tubing so as to prevent any possibility of a crossed or short circuit occurring. The various pieces of apparatus should be arranged so that all the necessary connecting wires will be as short as possible. Furthermore, to present a neat appearance, all wires should be run in straight lines and turn at right angles. Try to avoid running two or more wires parallel to each other for otherwise inductive interference between the several wires is likely to cause serious trouble. For the same reason all wires should be arranged to cross each other at right angles. Often a change in the value of the grid leak resistance will add greatly to the better operation of the set, for if the resistance of the leak is too low the negative charges will not accumulate sufficiently on the grid but leak off too quickly. This, of course, will not allow the plate circuit current to be affected with maximum intensity. On the other hand, if the grid resistance is too high, the negative charges will experience too great difficulty in escaping between wave trains. The result is that an excess negative charge will accumulate on the grid and choke the tube, thereby greatly interfering with the best functioning of the tube. Hence, since each tube has its own individual peculiarities as to the best filament temperature, plate potential and grid leak resistance, the operator will get best results by experimenting with these various factors until maximum intensity of signals will be received. After he has once determined these values, he can quickly set the adjustments to these values each time the set is set into operation. The essence of a vacuum tube is the filament, and the life of the filament depends upon the temperature at which it is operated. Consequently an important rule to observe in operating a set is never to burn the filament at a greater brilliancy than is -necessary to secure best results. If the filament can be burnt at a lower temperature, the life of the tube will be greatly prolonged; but if the filament is burned at too high a temperature, the tube life will be greatly decreased. Another important point to observe is never to connect the B battery across the tube filament or A battery terminals, for the high pressure of the B battery will cause such an excess current to flow that the filament will be burned out immediately. The same may happen if the interior wires are not insulated and should accidentally come in contact. If all the above suggestions and warnings are carefully observed and followed, successful operation of the outfit is bound to be secured. However, a little slip here or there may so seriously interfere with the functioning of the various parts, that many an evening's pleasure can quickly be spoiled. Chapter Eleven In the next chapter we will consider the second important function of the vacuum tube, namely its action as an amplifier. We will discuss the general subject of amplification, and show how additional vacuum tubes can be used to intensify the signals detected by the detector tube. It will be a most interesting and important article. of the wires, but this is guarded against by an electric heating circuit which melts the ice as fast as it collects. Signals from Annapolis have been heard in Australia. Homemade Battery Switch Procure two small strips of light copper sheeting and bend the ends of each as shown and drill the holes marked. Bend the edges of both pieces so that there will be a pocket for the plunger end. Procure a piece of copper wire, number 6 or 7, and thread one end to fit the nut or knob of a binding post. Bend the opposite end over to make it double and round off the end. This makes the plunger. When the plunger is pushed in the connection is made. — Daniel H. Mowat, Joliet, 111. VARIABLE CONDENSERS 43 Plate *<$}» $1.65 23 Plate *858i" $1.45 3-in. Dial, to fit, 25c Fully Guaranteed. Money Order or Check. Morganson Eng. Co. gB^"10!?. v.' GOV'T. RADIO STORAGE BATTERIES New Signal Con>s Batteries. Edison 3 cell type BB-4. $4.50; Edison single cells for W.D.-ll tubes, $1.50; Edison 60 A.H. for W.D.-ll tubes, $5.25; 6 Volts Edison, $7.75; "B" battery Edison single elements. 4o ea. ; double, 10c ea, PEANUT TUBES Wonderful det. and amplifier, smallest tube made; aeroplane style. 1 V„ y* Amp., %" dia. x 2^" long. Just a few at $9.50. Ack Quick if you want a real pocket set tube. FUUjY GUARANTEED. FLEWELLING .006 CONDENSERS & PARTS .006 Bakelite mounted Kuby Mica-Copper. N. P. binding posts, set (3), $2.90. Var. Grid Leaks (cleaver music, louder signals on any cir. ), 75c. Var. Grid Cond., .00025 or .0005 max., 45c Special Audio Trans.. $3.45. Spider coils. Easier tuned, clearer signals; green silk on Bakelite, $1.75 ea. REINARTZ LATEST COILS Double green silk wire on polished Bakelite spider, $1.95. Reinartz plate circuit chokes (triple adjustable*. $1.70. RADIO FREQUENCY IRON & PARTS .003 Iron for cores; special wire and forms to construct B.. F. Transf. of highest efficiency. Detailed plans, 50c. REFLEX CIRCUIT TRANSFORMERS Special Reflex Trans. & Dlag. that really works. $3.65. VERNIER FOR VARIABLE CONDENSER Works with any condenser. Requires no extra space, 95c. HI-POWER AMPLIFYING TRANSFORMER Best! Loudest! No burn-outs. $2.95 with spec diagram. 20 OHM RHEO. FOR 201-A OR WJX-11 tubes, $1.60. 8 ohm for new DeForest tubes, $1.55. Include Postage with order. Write for complete list QUALITY RADIO SHOP, RICHMOND, IND. Simple Construction of Variocouplers Rotors One of the simplest and easiest ways to make a variocoupler or variometer rotor is to use an old croquet ball as a base. Place the ball in the top of a standard Mason fruit jar and mark a ring on the ball. Saw it off, and then mark another ring on the opposite side of the ball, parallel with the first ring. Cut this portion off also and the rotor section will be the right size. In boring the shaft hole, wrap a slip of paper around the circumference of the rotor and mark the length on the paper. Divide the paper in half up to the mark and place the half on the ball. Make a mark at the ends and these will be the through the bearings, or a hollow shaft Bore two holes, % or 1 inch through the parallel faces to intersect the shaft hole. These are used for leading out the connections. The end^ of the winding can be soldered to the shafts and so taken out through the bearings, or a holllow shaft can be used, and the wires run through it. When starting the winding either tack a circular piece of cardboard on each parallel face so as to project about % inch all around, or put small brads around the edges of the rotor. These will hold the windings in place temporarily. When the winding is finished, paint it with water gla^s — sodium silicate. The water glass dries with a hard, glassy surface, which will hold the windings in place permanently. The brads or cardboard can then be removed. An oatmeal box or a salt box can be shellacked and used as the tube with this rotor. — G. F. Lamkin, Cincinnati, Ohio. A bulb that gives a weird, blue glow when in use indicates that an over-supply of current is coming from the B battery. IMPROVED RADIO DETECTOR TUBES IMPROVED RADIO AMPLIFIERS Sent on receipt of price, prepaid LUX MANUFACTURING CO. $2.75 $3.35 1045 No. Wells St. CHICAGO, ILL, Radio Distances Easily Read Use Cram's Detailed Radio Map covering the United States and Canada. Just one hundred miles to the inch. Map plate 30x20 inches, on sheet 34x28 inches. Latest call numbers at sides and bottom. Used by Radio Digest and other Radio Experts. Radio Districts and headquarters and time divisions. New edition now ready. ' Ideal for the purpose. POSTPAID Pocket Form $0.35 Heavy Paper in Tube 50 Wall Style Wooden Rollers.... 1.50 On Heavy Board for Tacks 6.75 Special quantity prices to trade and advertisers The George F. Cram Co. Ill N. MARKET STREET DEPT. RD CHICAGO, ILL. Delicate Soldering Both the manufacturers' and amateurs' problems on all fine work are readily solved by the instrument constructed for this particular purpose. THE POST SOLDERING IRON Platinum Heating Unit — Interchangeable Tips — Universal Current Large & Small 6Vy ONE-HALF ACTUAL SIZE Awarded Certificate of Excellency, N. Y. Evening Mail Radio Institute From your Dealer, or write POST ELECTRIC COMPANY (Dept. 509), 30 E. 42nd St., New York TOHj