Triplett 631 VTVM-VOM Analog Vacuum Tube Voltmeter Volt Ohm Meter 11 Meg

Triplett 631 VTVM-VOM Analog Vacuum Tube Voltmeter Volt Ohm Meter 11 Meg

The Triplett Model 631 is a combination vacuum tube voltmeter and volt-ohm-milliammeter (VTVM-VOM) in a single portable instrument. Produced by Triplett Electric Instrument Co. of Bluffton, Ohio, the 631 combines the high input impedance of a vacuum tube voltmeter — 11 megohms in VTVM mode — with the flexibility of a conventional VOM for resistance, current, and lower-impedance voltage measurements. The meter face carries the Triplett Red Dot Lifetime Guarantee badge and features multiple arc scales covering DC voltage, AC voltage, resistance, dB, and milliamps.

Specifications & What's Included

• Manufacturer: Triplett Electric Instrument Co., Bluffton, Ohio — Made in USA
• Model: 631 VTVM-VOM
• DC Voltage Ranges: 0–3, 0–12, 0–60, 0–300, 0–1200V
• AC Voltage Ranges: 0–3, 0–12, 0–60, 0–300, 0–1200V
• VTVM Input Impedance: 11 Meg
• VOM Ohms Per Volt: DC 20,000 / AC 5,000
• Resistance (Ohms) measurement via dedicated Ω ranges
• Current (mA) ranges visible on selector
• dB scale on meter face
• Front panel controls: ZERO ADJ, Ω ADJ (zero ohms), TEST B+ jack
• Large rotary range selector knob with DCV, ACV, ohms, and mA positions
• Input terminals: VTVM, COM, V-Ω-A (two sets for VTVM and VOM)
• Form factor: portable with leather carry handle and black bakelite case
• Meter only — no test leads, probes, or manual included

Applications

The Triplett 631 dates from the mid-20th century era when vacuum tube voltmeters were standard bench instruments in electronics service shops, radio and television repair, and laboratory work. A VTVM's high input impedance (typically 10–11 megohms) made it far less likely to load down the circuit under test compared to a conventional VOM, making it the preferred tool for measuring voltages in high-impedance vacuum tube circuits. The 631's combined VTVM-VOM design gave technicians both measurement modes in one instrument — useful for everything from aligning AM/FM receivers and television sets to servicing early test equipment and industrial electronics. Today these instruments are collected by vintage electronics enthusiasts, used by restorers of antique radios and tube amplifiers, and occasionally pressed back into service for period-correct repair work on vintage vacuum tube equipment.