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Radio Record, Volume II, Issue 6, 24 August 1928, Page 9

WNERS of erystal sets who desire to add a stage of audio amplification cannot do better than employ a double grid valve. These fit standard bases, the auxiliary grid being connected by means of a terminal at

the side of the valve to the positive: terminal of the high tension battery. These valves give an amplification factor up to a hundred with consumption as low as .06 amperes at four volts, thus permitting an accumulator to be dispensed with.