n.4 o POPULAR MECHANICS

Flashing Lights 'I By Albert L. Daugherty

DESIGNED for t e ach ing the prlnclples of the vacuum tube,

and a one-tube receiver in radio and science classes, this visual demonstration unit is housed in a l a r g e brightly painted cab ine t . The wiring d i ag ram is made of copper, tubing and the various ele- ments have openings behind their diagrammatic r ep r e sen t a t i on through which lights shine in the same sequence as the electric im- pulses travel in a real receiver. The openings are covered with red, yellow and green Cellophane so that the cliirerent electric circuits are easily traced as a revolving switch moves from one set of con- tacts to another. When the "phone" lights go on a buzzer sounds to indicate that the program is coming in. Photos A and B show front and rear views.

KEY TO FIG. 1: I-panel; Z-cabinct : 3-Incoming ra - dio wave; 4-R.F. current: 5 and la-+oils: 6--port for liaht; ?-grid condenser and grid leak: &port: 9-vari- able condenser; 10-area painted to indicate triode tube: 11-fllarnent; 12-arid symbol: 13-translucent mirror for Plate; 14-area with green Cellophnnc; 15--slot for grid liaht: 16-area behind plate, yellow Cellophane: 17--cond~nser: IS-actunl phone caps with yellow lights in place of diaphragms: I!l-yellow for B battery: 26- red for A battery; 21-holes representing electrons pass- Ins from filamcnl; Z%t~oles In panel for electrons going lo plate; 25--cord for 115-v supply for lights and switch

APRIL, 1941 615

HOW TO SAVE MONEY ON I Miniature-Tube Flashlight Cell Receiver

EVERYTHING IN RADIO

New K i t s ! (;i,t :!,? t l l ~ i i l oi 15.000 Parts! '11161 I l izxest s t . 1 ~ ~ - lt!ti l<!i!w >m~ttr m v t l r z ' i i o ! I ) $ r ~ t , l ~ < t ~ o u of q!$:!li ls nilr l% i t , a i l r,sdiu. f v I s - I - 1 1 1 i I l k t I:ii,rs Iv;lti inx 111i8k<: - (~01111111~1~ t o s i c f t - i s I I - l l s t inxs ful. P i r r s ~.;ttiio hr~ii,i in!: s ign%: I.'ltl.:l: I'icl'ls 1.isrs nu re- it1111 se~.vic.it,n r c q t ? i r r ~ t ~ ~ ~ n l . t:vpl)-~ I - I i I I i Lhi l tx SOII 18rwl at SIIIII. t irt~el.ti l)s. r:tdio for c!?rY I l L ~ i I ~ l t ! ! ~ rv<luI~'c- l>ott ' t !miss th is 7 x ~ l ! l l l S l ? r l r ~ x I . I l l X I I r y k - :\I.I,I F:l) (';11;110p - llle rt.lj:tltlc, 1s l o furl ;111,I ~1.rlfirs nllel! J(IU rrls ( l<t i<ie 10 K ~ c r s t l > i t t c i n I l : ~ < l i o a1 un i\I,I.lF:I) to hc l l l xu"! ti le lotvc.;t pl.i<ws!

Radio Dict iansry. S o t h i n g I ~ k e i t ever irrf0rr.-rolnplrle, s l l t i l o r i - ti lt ivll. !l.nrll1 n l i l l l ~ l i ~ n e s t l lc n r i c r ! V n r n n l i ~ ~ ~ I I,? l?acIirlg I<;ulio :111111orili~1 ~l l l t l<,r ;\T,LII:l) strncr-

Bui lders ' Hantlbook. The n ~ s t ~ ) ~ l ) t , l i $ r and l i t l t , l ? S O I ~ 01 i l l1 1t;tclio n ! ~ l ~ l i ? ; t l i ~ ~ ! ~ ~ - ,\l.Llb;I)'s a\rn ralual j le b ~ ~ g i r l l l e r ' s hook oo 1t;~dio. TVIIP I1c11v to SelecL e i r - cttits, rc.?<I di;fi$rdnls. lmi lc i ~ ~ ~ 1 ~ . 1 . In t r l . r s t i ! l r .\lnatcur I l i l t l l r l wct inn. I.',~lly i l l u s I ~ ~ i ~ t ~ i i , l i i tsy l o ttn~Ier?t.~ncl. 3l : tk~s i t easy 1 0 learn l i ;~ , l i o Send roupon SO\,'! ............. 1 0 ~

I Sc,!~<l 1 ~ - sot~v l~'itlCi2 1!111 Spr ing ( 7 a t a l ~ ~ . " I 6mvlad. l n c fur 1l:gdio Diorionnry. O I cllelose I l l c fur I ldcl io I l l 8 i l~ lv r r ' ~l:ln~ll~ook.

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(Continued from page 617)

the 3-circuit-tuner type which has a ter- minal strip clearly marked for proper con- nections, greatly simplifying the circuit wiring for the novice. In addition, the coil has a movable "tickler coil" which makes the usual volume control or variable con- denser for controlling regeneration unnec- essary. Two small machine screws are used to bolt the coil assembly to the front panel. Finally mount the row of Fahnestock clips with machine screws and nuts, placing a round-hole soldering lug under each nut. One extra clip is mounted to connect in the negative-B lead so that when the loud- speaker stage is added it can be controlled

by the same "on-off" switch. The small round tuning dial plate is fastened to the front of the panel with china cement.

In assembling and wiring these units, follow the diagrams carefully, checking each wire as you put it in. Make all con- nections with rosin-core wire solder mak- ing sure that your iron is bright and we11 heated. Good mechanical and electrical connections are important in radio work. Although all parts for both receiver and audio amplifier arc i n e x p e n s i v e , they should be of good quality, and just as specified. A detailed list of the original parts used in both units, is available from Popular Mechanics radio department with- out charge.

After the receiver is wired, you are ready to solder the flashlight batteries to- gether. Scrape the ends with a sharp knife where they are to be soldered to insure a good connection. It will be noted that two of the cells are connected in parallel for the 1% volt "A" battery. Conl~rctcd in this manner the voltage remains at 1% volts but the amperage is increased to double the usable life of the cells. Use a good set

(Continued to p a p 136A)

134A POPULAR MECHANICS

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(Continued from page 134A)

of, preferably new, 2,000-ohm headphones; old phones usually lack sensitivity. To test the receiver, connect the antenna, and a good ground on a cold water pipe; throw switch No. 1 "on" and turn the "tickler coil" until it lines up with the large coil. Now rotate the variable condenser slowly. Whistles indicate stations. When one is heard, rotate the "tickler coil" until the whistle stops and the station comes in

clearly. To tune in short-wave stations, throw switch No. 2 and tune slowly and carefully as these stations tune very sharp. Best results on the short wave bands will be obtained a t night, especially the ama- teur and police stations. Some of the type IS4 tubes seem to operate more smoothly on 4% volts of B-battery. If the set "pops" noticeably as the coil is turned, or breaks into squeals, use three of the cells in the B-battery instead of the four shown.

Construction details for the amplifier unit are clearly shown in Fig. 3 and the battery connections for using both units in Fig. 3-A and photo B. It will be noted that a large No. 6 dry cell is used for the A-bat- tery and that a 4% volt "C" battery and a 45-voIt B - h a t t ~ l . ~ arc added: t h e No. 6 dry cell replacing the two-cell flashlight A- battery in order to operate both units more economically. Schematic circuit diagrams for both units appear in Fig. 4. The blue- print number of this article is R-289.

POPULAR MECHANICS

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APRIL, 1941