Description
Simpson 311 Vacuum Tube Volt-Ohmmeter VTVM AC DC Ohms 1.5-1500V 22 Megohm Analog
The Simpson 311 is a classic vacuum tube volt-ohmmeter (VTVM) manufactured by Simpson Electric Company of Chicago, Illinois. Unlike a conventional multi-meter (VOM), the 311 uses a vacuum tube amplifier circuit to present an exceptionally high input impedance to the circuit under test — 22 megohms on DC — which allows accurate voltage measurements in high-impedance circuits without loading them down. It measures AC voltage, both positive and negative DC voltage, and resistance across a wide range of scales.
Specifications & What's Included
- Make: Simpson Electric Co., Chicago, Illinois — Model 311
- Type: Vacuum Tube Volt-Ohmmeter (VTVM)
- DC Input Resistance: 22 Megohms
- AC Input Impedance: 10 Megohms at 60 Hz
- Voltage Ranges: 1.5V, 5V, 15V, 50V, 150V, 500V, 1500V
- Resistance Ranges: Rx1, Rx10, Rx100, Rx1K, Rx10K, Rx100K, Rx1M
- Function Selector: +DC, -DC, AC, Ohms, RF Probe position
- Controls: Zero Adjust knob (left), Ohms Adjust knob (right), range selector, function selector
- Display: Large multi-scale analog meter movement with mirrored arc
- Portable carry handle on top of metal case
- Power: AC line powered (standard 120V AC)
- Country of Manufacture: USA
- Includes: Test leads (see condition note — lead insulation is severely damaged and leads require replacement)
Applications
The vacuum tube voltmeter was the standard high-impedance measuring instrument for electronics service work from the late 1940s through the 1970s. Its 22-megohm input impedance made it the go-to tool for servicing vacuum tube radio and television receivers, where probe loading could cause false readings with a conventional VOM. The Simpson 311 was widely used by radio and TV technicians, ham radio operators, and electronics hobbyists throughout this era. Simpson Electric was one of the most respected names in American test instrument manufacturing, and the 311 was among their most popular VTVM models. Today these instruments are sought by vintage electronics restorers, tube radio collectors, and those who service and maintain period equipment where a high-impedance meter is still the correct tool. The VTVM was eventually supplanted by solid-state FET-input DVMs in the 1970s and 1980s, but many technicians working on vintage equipment still prefer the analog needle for intuitive readings during alignment and troubleshooting.
This Simpson 311 Vacuum Tube Volt-Ohmmeter (VTVM) has been visually inspected and photographed. The unit itself shows age-appropriate wear consistent with vintage test equipment of this era — the metal case has paint wear and general aging throughout. The test leads included with this unit are in poor condition: the insulation is heavily cracked and deteriorated along the length of the leads, with the inner conductor exposed at a break point (clearly visible in our photos). The leads should be considered non-serviceable and will need to be replaced before the meter can be safely used. The meter movement and controls appear intact. This unit has not been powered up or tested at our facility. Please review all photos carefully and contact us with any questions before purchasing.
Warranty Information
Additional Information
Brand: |
Simpson Electric |
Model: |
311 |
MPN: |
311 |
Type: |
Vacuum Tube Volt-Ohmmeter (VTVM) |
SKU: |
28886 |
Country/Region of Manufacture: |
United States |
Form Factor: |
Portable / Benchtop |
Measurement Type: |
AC Voltage, DC Voltage, Resistance (Ohms) |
DC Input Resistance: |
22 Megohms |
AC Input Impedance: |
10 Megohms at 60 Hz |
Voltage Range: |
1.5V, 5V, 15V, 50V, 150V, 500V, 1500V |
Resistance Range: |
Rx1, Rx10, Rx100, Rx1K, Rx10K, Rx100K, Rx1M |
Function: |
AC, +DC, -DC, Ohms, RF Probe |
Display Type: |
Analog Meter Movement |
Power Requirements: |
AC Line Power (120V AC) |
Seller Notes: |
Includes test leads (test lead insulation is cracked and damaged — see photos) |
Compatible With: |
General electronics service, radio/TV repair, vintage test bench |
Condition Notes: |
This Simpson 311 VTVM has been visually inspected. The metal case shows age-related wear. Included test leads have severely cracked insulation and an exposed conductor — they need replacement. Unit not powered or tested at our facility. |
California Prop 65 Warning: |
WARNING: This product can expose you to chemicals including lead and lead compounds, and DEHP (a phthalate), which are known to the State of California to cause cancer and birth defects or other reproductive harm. Go to P65Warnings.ca.gov |