Radio Broadcast - 1923, August - 86 Pages, 8.5 ... - VacuumTubeEra

326 Radio Broadcastinductance is variable by means of a tapswitch mounted on the back panel, whilethe secondary circuit is tuned by three condensers(two variable and one fixed). Theshaft of the variocoupler was lengthened toinclude the shaft of the three-plate verniercondenser which is thus made to rotate withthe coupling coil in such a manner that as thecoupling is increased, the vernier condensercapacity is decreased, thus tending to stabilizethe resonant point of the primary and secondarycircuits and helping to prevent detuningwhen the couplingischanged. In parallelwith this condenser is the main secondary condenserof thirteen plates which is in turnshunted by two .00015 mfd. condensers inseries. When the main secondary condenser isat full scale.set at o, the secondary wavelength is approximately80 meters and increases to 420 meters1If now one of the small mica condensersis cut out by the switch provided, thesecondary wavelength becomes 400 meters ato and increases to about 600 meters at fullscale. This arrangement givesa full verniereffect with a small variable condenser and stillprovides a large range of wavelengths.In case it is desired to use the tuning elementswithout the radio-frequency bank, ajack has been provided which enables a crystalor other detector to be plugged in. The tuningisaccomplished in the usual manner.In addition to the usual jack arrangementwhich enables the signals to be received oneither the detector or the first or second audioamplifiers, an additional jack has been providedso that an external detector can beplugged in on the audio-frequency bank. Thisjack in connection with the one associated withthe loop jack enables crystal reception, utilizingthe tuning elements with or without audiofrequencyamplification and makes an idealarrangement for local reception.A rather extensive system of voltage controlhas been provided and has proved to be anabsolute necessity. A o-io D. C. voltmeteris connected through a two-pole, triple-throw,cam-key switch to three separate circuits, oneof which follows along on a buss under the filamentrheostats, to which is connected six doublepolesingle-throw push-button switches whichare in turn connected, one to each of the tubesocket terminals. With the key in the properposition, pressing any one of the push-buttonswitches shows the voltage on the terminalsof its associated tube. A second circuit fromthe key switch goes to the A battery terminalsRfDIAGRAM OF THE RADIO- AND-