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Radio Record, Volume I, Issue 21, 9 December 1927, Page 13

= =| For crystal amplifiers employing an oidinary valve in the first stage, a grid bias of 14 volts will often be all that is necessary to improve the tone. This means that one dry cell which may be flashlight size is all that is required. To install this, find the secondary terminal of audio transformer connected to negative A and disconnect this wire, connecting it- instead to the positive of the 1}-volt cell. The negative side of the cell is then connected to the transformer terminal. It must be clearly understood that this connection is not to be made on the side of the transformer secondary that is connected directly to the grid of the valve. The higher the impedance of a valve, the lower the grid bias required. (End of Construction Section.)