Description
Simpson Electric 21-B DC Milliammeter Panel Mount -150 to 150 mA W.U. Tel.
The Simpson Electric 21-B is a round, panel-mount DC milliammeter with a center-zero scale ranging from -150 to +150 milliamps. This example bears the "W.U. Tel. Co." designation on its dial face, indicating it was calibrated and supplied for Western Union Telephone Company service use. It uses a classic D'Arsonval moving-coil movement to display DC current with a deflecting needle across the printed analog scale.
Specifications & What's Included
- Manufacturer: Simpson Electric Co., Chicago, IL, USA
- Model: 21-B
- Meter Type: DC Milliammeter
- Scale Range: -150 to 0 to +150 mA (center-zero)
- Movement: D'Arsonval analog needle movement
- Mount Type: Round panel mount with flange and mounting holes
- Dial Marking: "W.U. Tel. Co." (Western Union Telephone Co.)
- Scale Label: "MILAMMETER" / "DIRECT CURRENT"
- Terminals: Three rear brass binding post terminals
- Housing: Round black bakelite/metal case
- Front panel: Mechanical zero-adjust screw at bottom
- Included: Meter only — no mounting hardware or cables
Applications
Simpson Electric was one of the most prominent American meter manufacturers throughout the mid-20th century, and the Model 21 series panel meters were widely used in telecommunications, industrial control panels, and laboratory settings. The center-zero (-150 to +150 mA) scale is characteristic of meters designed to measure current flowing in either direction, making them well suited for battery charging/discharging monitoring, bridge-circuit null detection, and telecom line current measurement. This particular unit was sourced for or calibrated by Western Union Telephone Co., reflecting the broad use of panel meters in central office and field telephone equipment of the era — roughly mid-20th century. Today, vintage Simpson panel meters are sought by collectors of antique test equipment, by restorers of period electrical and telecom gear, and by hobbyists needing reliable analog current indication in custom panel builds.
This Simpson Electric 21-B DC Milliammeter has been inspected and is in good used condition. The meter face is clean and fully legible, with the needle and scale intact. The round black housing shows light wear consistent with age and prior panel service. The rear binding post terminals show some patina and oxidation, as visible in the photos. The unit was not powered up or tested at our facility, but shows no obvious physical damage. Please review all photos and contact us with any questions.
Warranty Information
Additional Information
Brand: |
Simpson Electric |
Model: |
21-B |
MPN: |
21-B |
Type: |
DC Milliammeter |
SKU: |
47558 |
Measurement Type: |
DC Current |
Measurement Range: |
-150 to 150 mA |
Scale: |
Center-zero, -150 to 150 mA |
Display Type: |
Analog Needle / Pointer |
Mount Type: |
Panel Mount |
Movement Type: |
D'Arsonval / Galvanometer |
Meter Face Label: |
W.U. Tel. Co. (Western Union Telephone Co.) |
Country/Region of Manufacture: |
United States |
Form Factor: |
Round Panel Mount |
Seller Notes: |
Meter only — no mounting hardware or cables included. |
Condition Notes: |
This Simpson Electric 21-B DC Milliammeter has been inspected and is in good used condition. Face is clean and legible; housing shows light wear. Rear terminals show patina. Not powered at our facility. Please contact us with any questions. |
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 |
