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General Radio 1230-A
Electrometer and DC amplifier
General Radio 1230-A Electrometer and DC Amplifier

Available from 1956 to 1968

Catalog History
 Document Year Page
Catalog O 1956 2
Catalog P 1959 130
Catalog Q 1961 128
Catalog R 1963 140
Catalog S 1965 174
Catalog T 1968 239
(All manuals in PDF format unless noted otherwise)

The General Radio 1230-A Electrometer and DC Amplifier was introduced in Catalog O (1956) and remained available through Catalog T (1968).

The Type 1230-A is laboratory instrument designed for the measurement of extremely small voltages or currents and conversely extremely large resistances. It achieves this with the 5886 electrometer vacuum tube used in the first stage of amplification. The combined gain of the three stages result in a transconductance in the millions of μS. The output of the amplifier is read from the panel meter, or an optional recorder connection at the rear panel. The recorder terminals are in series with the meter, so a resistor is required without a recorder connected.


  • Voltage: ±30, 100, and 300 mV, ±1, 3, and 10 V DC full scale
  • Current: ±1 mA DC full scale, to ±0.3 pA full scale; Measured in terms of voltage
  • Resistance: direct reading from 300  kΩ to 10 TΩ full scale in 16 ranges, two per decade. Voltage across the unknown resistance is 9.1 V
  • Voltage: ±2% of full scale on the five highest ranges, ±4% of full scale on the 30 mV range
  • Current: ±3% of full scale from 1 mA to 1 nA, ±10% of full scale from 300 pA to 0.3 pA
  • Resistance: ±3% from 300 kΩ to 10 MΩ at full scale (low-resistance end), ±8% from 3 MΩ to 10 TΩ