Radio City Products 665 VTVM
Overview
The Radio City Products 665 is a mid-1940s combined vacuum-tube voltmeter, ohmmeter, capacity meter, and insulation tester (megohmmeter) — the oldest instrument in the collection, advertised in *Service* magazine in October 1944. It earns its bench slot in 2026 because it still works and does things a modern DMM does not: an ~11 MΩ-class input that doesn't load high-Z tube-radio grid circuits, and an in-probe-tip RF rectifier topology that keeps RF off the meter lead. Migrated here from the Scanners bench-instrument volume (2026-06-15).
Context
Radio City Products Company of New York operated from the early 1930s to ~1970, building the full radio-service-shop instrument line. The 665 was marketed as an insulation tester (its headline megohmmeter function, up to 500 V / 10,000 MΩ) with VTVM, ohmmeter, and capacity-meter functions alongside. Documentation in 2026 lives almost entirely on Radiomuseum.org. Exact revision, tube complement, and battery state are bench-verification TBDs carried inline in the volumes.
