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Show USE POTENTIOMETER TO ADJUST BATTERIES 1 1 BY PAUL F. GODLEY. Atnerlca's Foremost Radio Authority. To all those who are using vacuum tubes In their radio work, tho use of the rhoostat for adjustment of filament fila-ment currents 13 well known. But i here seem to be many who do not understand un-derstand or appreciate the utility of tho device which Is known as the "A" battery poleniinmoter for adjustment of the "H" battery. For this work potent lometers of various va-rious types have been tried. In the main they have consisted of a high-resistance high-resistance unit, which was placed eli her in series with, or in shunt to, tho "B" battery. When in merles, much larger batteries thnn the normal j ones were necessary to overcome the added resistance of the unit When In shunt, due to the high volt i age employed in the plate circuits of; the tube, considerable energy was Woetefl in the potentiometer unit I This was particularly objectionable since the capacity of the battery com-' monly Called upon for this work was! very smail often of the flashlight bat-i tery size 6v H'I'tf T- HSMNMMWtisL C PoUrAiocwtar' T ( Connecting potentiometer for adjustment ad-justment of "B" battery. The "A" battery potentiometer Is; connected directly across the "A" orj filament lighting battery. This bat-; tery is usually six volts. If tho resistance re-sistance of the potentiometer unit is o00 ohms or more, the amount of current cur-rent flowing through it is entirely negligible. neg-ligible. It would require many weeks ( to completely discharge a storage bai-, tery through such a resistance. But the effect of tho potentiometer BS connected iu the accompanying circuit cir-cuit is all that can be desired. I It enables the addition to, or tho subtraction from the "B" battery of L.. the "A" battery voltage Mm For example, when the potentiometer poten-tiometer slider is at the extreme right, the circuit from the plate through the telephones to the filament includes the full 22tt-TQlt battery and the full six-volt battery. When the contact of r tho potentiometer is slid to the ex- i treme left on the negative terminal of i'io "A" battery, the potential ot the "A" battery, the potential of the "A" ( battery is opposed to that of the "B"' with a corresponding reduction of the total potential in the plate circuit. CONDENSER. The capacity, C, connected as shown, is essential for proper operation opera-tion Lacking it, there- will be considerable consid-erable resistance offered to the high-frequency high-frequency currents which flow in the plate circuit. Its value need not be greater than .0005 MF, although a I I much larger condenser may be used. For tho, operation of the sensitive ; ; "gassy" tubes usually used for detec- j! HI tor purposes, the potentiometer is of great value. H |