Show by CHESTER CHARLTON in radio world the one hour bet Is not one that simply lasts an hour but one that it takes only one hour to make it will last for many years and will render ex cellena service the radio side of the circuit consists of the justly famous three clr cult tuner the audio channel corn arises two stages of transformer coupled amplification fience the three tubes all three sockets are a part of the detector amplifier unit only the radio side need be wired the only change I 1 made was to cut the one inch lead that comes from the F posts of the two audio transformers to insert a 0 battery as shown in diagram coll information any of the commercial three circuit tuning colls may be used in this clr cult the one shown tunes with a mad variable condenser it has 6 pancake tickler however some other sort of tickler will do as well for instance it you wind your own coll you may use a 3 inch diameter tubing tor the stator 4 inches high placing 10 turns of ho 24 double silk covered wire near the top LI ter malnate leave inch space and wind 5 turns of wire in the same direction for the secondary la 12 the tickler would consist of as many turns of the bame kind of wire as you can put on any tubing that will rotate inside the secondary remember that a shaft has to pass through the secondary hence wind the tickler coll so as to leave anchorage room thereon tor the shaft where it must be joined to the tickler form A capacity tuning con denser was semi r plates the fact that the coddens er has an insulation end plate does not mean that the condenser Is not low loss it Is to make the tuning more standard type of tuned radio frequency outfit the growing tendency to use high voltages in audio frequency amplifiers often results in the application of the same voltages to the radio tre quincy tubes due to the fact that separate binding posts for the radio frequency and audio frequency B post alve taps are not provided for in many sets the accompanying illustration shows a convenient end practical method of varying the voltage on the radio fre quency tubes by the use of a high resistance the circuit shown Is not new but Is a standard type of tuned radio frequency outfit illustrated to show where the high resistance should be method of varying voltage en cadlo frequency connected in such a set the same idea la explicable to intermediate stages of a or to other forms of radio frequency ration whre the amplification voltage Is bet sen 00 and the resistance may be TOO ohms maximum although much cowf values usually will give the desired results the principal point to n considered in choosing such a re Is its ability to go down to low values of resistance etota that the variable resistance Is asa convenient on the lower waves and yet avoid crowding on any part ol 01 the dial a converted dial was used the parts needed you need get oni a 7 by 18 inch panel a mad variable condenser a dial vernier it you use frequency con den sers or a converter a 7 by 17 inch baseboard a grid leak and a knob the layout of the parts Is very alm pie As the condenser Is the only real tuning element it alone has a dial the tickler coll Is turned by means ol 01 a knob even a rheostat knob or if desirable si a 2 inch dial may be used here the rheostats jack and even the fixed condensers including the grid con denser are part of the detector ancill fier unit the wiring precautions include these connect the rotor plates of the variable condenser to the grid return side of the coll 12 the 45 turn coll if you make your own this Is the con made to A plus connect the aerial coll BO that the ground and A plus connections adjoin this accounts for two terminals one each of primary and secondary and the other connect of these windings go to aerial and grid condenser respectively the tickler or movable coll may be joined to the plate of the detector tube in either manner that Is either terminal to plate actual time 57 minutes the set shown in the photographs wag completed in 57 minutes but wo will call it an hour this included the drilling of the panel and the mounting of the dial two items that require a little care and hence took a good fraction of the time there are only about a dozen connections to make i the leads are brought opt to binding posts on the unit and a marked battery cable should be used for convenience in establishing con facts at the batteries connected in series with the supply to the radio frequency tubes only the 00 volt tap in the illustration connect ing to the audio frequency tubes dl recal any variable rosl stence of suitable value may be used in this manner to control voltage on R P tubes the 11 shows the Centra lab resistance si the Bradley ohm and the are others which should serve satisfactorily cleveland news why your radio tubes need filament light the tact that a radio bulb does emit light Is entirely an incidental feature of its operation what Is desired in a tube Is a flow of little particles of electricity called electrons and the easiest way to obtain it Is to burn certain kinds of wires in glass bulb from which the air has been ex hausted the temperature must be quite hagn in order to make the flow copious and most wires must be heated white hot by the current from the A battery tor proper operation of course the in candescent wire or filament as it Is correctly called emits considerable light but this phenomenon has absolutely no connection with the bunc of the tube from the radio standpoint it Is quite possible to obtain a stream of the minute electrons in a tube by the use of certain substances known as radioactive materials but their expense and rarity make their practical application extremely limited radium and radium compounds are foremost in this radioactive group so the cost of tubes equipped with filaments of this precious element can easily be imagined no A battery incidentally would be re quiren for beuch tubes as the flow of electrons from radioactive compounds Is automatic and continuous certain less expensive chemical compounds of high electron emitting properties have been successfully employed ip radio tubes the wire which ordinarily must be burned at white heat la coated with a layer of one of these compounds and the tub Is then operated at a dull cher ry red heat in many of the modem tubes of both the coated and uncoated vart atles little or no light Is visible through the glass because of the in ner coating of mercury which alnea the bulbs the heaviness of coating varies considerably as will therefore the amount of light thai penetrates through it so no cance can be attached to the bri bance of the illumination |