Overview
The Trio SP311 is a vacuum tube voltmeter engineered for precision AC voltage measurement in the 0–3 volt range. Trio Laboratories designed miniature panel-mounting AC vacuum tube voltmeters for applications where high sensitivity and reliability were critical. The SP311 delivers accurate analog readout for low-voltage AC measurements in laboratory, industrial test, and maintenance settings.
Key Features
- 0–3 volt AC measurement range with sensitive scale
- Vacuum tube circuit design for stable, drift-free operation
- Analog needle meter display for intuitive readings
- Compact panel-mount or benchtop configuration
- High input impedance typical of tube voltmeters
- Precision measurement capability for low-voltage AC circuits
Technical Specifications
| Measurement Type | AC Voltage |
| Voltage Range | 0–3 volts AC |
| Display Type | Analog Meter (Needle) |
| Circuit Technology | Vacuum Tube |
| Manufacturer | Trio Laboratories, Inc. |
| Model Number | SP311 |
Typical Applications
- Laboratory AC voltage measurements in low-voltage circuits
- Audio frequency testing and analysis
- Vintage electronics repair and restoration
- Precision measurement in research environments
- Field testing and troubleshooting of AC power sources
- Instrument calibration and verification
Compatibility & Replacements
Compatible With
- Standard laboratory benchtop power supplies (AC output)
- Function generators with AC output capability
- General-purpose AC measurement systems
- Vintage electronic equipment testing setups
Replaces / Drop-In Replacement For
- Other Trio Laboratories vacuum tube voltmeters in the 0–3 volt range
- Equivalent precision AC voltmeters with similar sensitivity
- Note: Verify compatibility with your specific application before ordering
Works With
- AC power sources (50–60 Hz or wider frequency range depending on tube design)
- Impedance-sensitive measurement circuits
- Legacy laboratory and test equipment ecosystems
- Stand-alone measurements or integration into test racks
