1864

The GR Type 1864 Megohmmeter was introduced in Catalog U (1970). It is still available from IET Labs as of 2024.

Specifications

• Test Voltage: 10 V to 109 V in 1 V steps, 100 V to 1090 V in 10 V steps; 5 mA limit
• Resistance Range: 50 kΩ 20 200 TΩ in 8 ranges

Links

• The Model 1863 is similar but with a 20 TΩ top range, and a choice of only five test voltages (50, 100, 100, 250, or 500 V).

Internals

The 1864 is solid-state except for the test voltage supply pass element, a 6AB4 (EC92) vacuum tube.

Current through the unknown is converted to a voltage using decade reference resistors from 2 kΩ to 2 GΩ. In the highest range (10 TΩ multiplier), feedback is used to multiply the effective reference resistance by a factor of 10.

A four-stage, FET-input amplifier drives an analog meter.

Photos

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  GR-1864 schematic