[Test-Equipment] GR 1800A VTVM

[Dale H. Cook]

At 11:02 PM 12/17/2013, Richard Knoppow wrote:

>... which is threaded in the center for the outer shell of a type 874 coaxial connector.

The GR Type 1800-A predates the Type 874 connector series, whose center conductor is a four-part genderless design which is essentially a miniaturized version of its outer conductor.

The first option for the Type 1800-A probe is as a Type 274-M plug, which is a double banana plug.

The second option fits the probe as a Type 774 plug, which is essentially a shielded banana plug. The Type 774 was the standard RF connector on GR instruments of the '30s and '40s, including the Type 916-A and 916-AL Radio-Frequency Bridges, the Type 821-A Twin-T Impedance Measuring Circuit, and the Type 805-C Standard Signal Generator. After the Type 874 was introduced the later production of some instruments that originally used the Type 774 was converted to the Type 874. I have seen instruments that were manufactured with a Type 774 jack that had been field-converted to later RF connectors including SO-239 and BNC. Many years ago an article in one of the amateur radio mags (I think it was CQ) on the 821-A described how to home-brew a connector to mate with the Type 774s on the Twin-T.

Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcity/radios/radtop.html