Radio broadcast .. (1922-30)

5O2 Radio Broadcast transformers, etc. have been mounted. Likewise, all possible wiring should be put in place on the sub-base before it is finally screwed to the panel. If this is done, only a few leads will have to be run from the panel to the baseboard and the wiring will be found quite simple and easy. The wiring may be done with bus-bar, straightened, bent at angles and soldered to lugs fastened to the instrument binding posts, or it may be done with flexible n.agnet wire covered with spaghetti, as described in the October article. A C battery is used on the intermediate amplifier tubes as well as on the audio amplifier tubes. For uv-2Oi-A's this C battery will vary between 3 and 4^ volts. The same values will hold for uv-igg or ov-3 tubes, while the C battery value for WD-II'S, or wo-12's will range from if to 4^ volts. In each case the C battery is connected with its negative terminal to terminal 6 of the radiofrequency transformer unit and its positive lead to the center contact, or arm of the potentiometer. The audio amplifier C battery is connected with its negative lead to the F terminals of the audio transformers and with its positive lead to the minus side of the filament line. The C batteries may be located on the right hand corner of the base board inside the cabinet. If a high value of C battery is used on the intermediate amplifier, the potentiometer will have no effect on the volume of the set and a low enough voltage to permit of the potentiometer volume control should be used. It will be noticed in Fig. 3 that three bypass condensers are used, each of \ mfd. One is connected across the go-volt B battery, one across the 45-volt B battery section and one from terminal 6 of the radio-frequency transformer unit to the minus side of the filament. The cans of these condensers are soldered together, and with the cans of the audio transformers and the radio frequency transformer unit, are grounded to the negative side of the filament. This is very important; instability of the set may be due to the failure to ground all of these cans. If meters are to be used in the set, a voltmeter with a maximum scale reading of from 6 to 10 volts mav be connected directly across the A battr , terminals of the set to indicate the A battery voltage, or across the filament terminals of one of the tube sockets to read the filament operating voltage. This latter is the preferable position as it will permit operating the tubes at their best point, and resetting of the rheostat to the same value each time the set is used. A milliameter in the plate circuits of the tubes is of little value; a B battery voltmeter would be preferable. The B battery voltmeter may be connected directly across the B battery or it may have its negative terminal connected to the negative B terminal of the set and its positive post brought through the resistor to the center arm of a small single-pole doublethrow switch. If one contact of the switch is led to the 45-volt B post and the other contact to the go-volt B post it will be possible, by means of this switch, to throw the meter across either the 45 or go-volt battery sections at will. If a double range voltmeter is employed, a small switch can be used to throw it from the A to the B battery. The details of these circuits are given in Fig. 6. The advantage of bringing out the balancing condenser to the panel is that it permits maximum sensitivity to be obtained at every wavelength. If the balancing condenser is set at one fixed value, it will have to be at a point where the first detector tube will not oscillate at the shortest wavelength to be received. At the longer wavelengths the value of balancing condenser may be increased slightly with resultant strengthening of FIG. 5 The panel layout