Abstract
A kind of Vacuum Tube Potentiometer for determining pH or Eh of soil and other substances using ordinary Radio tubes (KX 12F and UZ 6C6) and a hady Spiring Ammeter is devised. A slight change on the grid voltage due to potential difference desired affects a considerable change of plate current by socalled A-class amplification. This change on the plate currcent canelled by a compensating potential difference. This compensating potential difference is read directly by a Voltmeter, the foregiven Ammeter being used. Usages and notices are given.
