The model 603 Electrometer Amplifier is a high gain amplifier and voltmeter for the frequency range of dc to 50 kilocycles. Its outstanding characteristics are an input impedance of greater than lO¹⁴ ohms shunted by 10 micromicrofarads, a grid current of less than 5 x 10⁻¹⁴ amperes, a maximum full scale sensitivity of 2.5 millivolts, differential input, low drift and a remote probe containing the first stage electrometer tubes. The remote probe allows the input grids to be located as far as 24 feet from the main amplifier. By employing this feature the input capacitance may be kept to a minimum so that it is possible to achieve fast voltage and current measurements in high impedance circuits., Current measurements, either differential or single-ended are made by inserting high megohm resistors in the place provided in the remote probe. The output capability of the Model 603 is 10 volts single ended or 20 volts pushpull at a maximum current of 10 milliamperes. The output is therefore suitable for driving milliampere recorders