Simpson's 311-2 is the bench VTVM counterpart to the [B&K 375](../B%26K%20Dynamic%20375%20VTVM/CLAUDE.md). Same role: ~11 MΩ DC input for tube-circuit measurements where a 20 kΩ/V VOM would load the circuit. Voltage ranges DCV ±1500 V (extendable with HV probe), ACV 1500 V, ohms from 0.1 Ω to ~1000 MΩ. Most copies of this unit in the wild still use the original 12AU7 / 12AX7 input cathode-follower and 6AL5 bridge — fully tube. Some late-production units swap to FET-input solid-state front ends while retaining the same panel layout.
The [B&K 375](../B%26K%20Dynamic%20375%20VTVM/CLAUDE.md) and Simpson 311-2 are kept side-by-side on the bench as a deliberate redundancy — two independent VTVMs let cross-checks catch a drifting calibration. The Simpson's specific advantage is the linearity of its custom-wound meter movement; the B&K wins on range count and the RF probe's frequency response. Common service issues: the input tubes (12AU7 etc.) drift over time and rezero is needed every couple of months; the carbon comp resistors in the divider chain go up in value; the internal battery holder corrodes.
A multi-volume deep dive on this instrument is in planning. When the first volume lands in the source project's 02-inputs/volume_sources/, this page upgrades automatically — no website code change required.