>The picture above is of a vintage Simpson Volt-Amp-Watt meter manufactured by Simpson Electric Company. This instrument provides an ac voltmeter, dc voltmeter, ac ampmeter, and ac wattmeter in one, compact convenient unit.
This instrument has a 3-inch meter of the dynamometer type that has a moving coil armature operating within two field coils. The meter scale has two arcs, one for Volts and Amperers, and one for Watts. The uniform wattmeter scale has equal divisions, permitting more accurate readings.
The instrument is supplied with a special break-in plug with four color-coded leads (shown in the picture above) for connection, permitting the appliance under test to be plugged in and reading taken under operating conditions without disturbing the circuit. The instrument terminals are arranged so that the instrument can be used test leads when the break-in plug is not used.
Below is a picture of the meter itself.
The available measurement ranges include:
| AC Voltage | 0-150V 0-300V |
| DC Voltage | 0-150V 0-300V |
| AC Amperes | 0-3A 0-15A |
| AC Watts | 0-300W @ 0150V line voltage 0-1500W @ 0-150V line voltage 0-600W @ 150-300V line voltage 0-3000W @ 150-300V line voltage |
The particular instrument I have incudes a leatherette-covered carrying case as shown below. The case includes three compartments, one for the instruction manual, one for the meter, and one for the break-in plug and leads.
Note that I have the original Operator's Manual (shown below) and break-in plug and leads (shown in the first picture above).
The instrument did not measure voltage correctly on the 150-V scale when I received it. Investigation revealed that a resistor was shorted to the 150-V terminal internal to the meter. Simply repositoning the shorted resistor away from the terminal fixed the problem. The pictures below show the meter reading correctly as compared to the voltage reading on my Fluke 87 DVM. The ac voltage reading is quite accurate. The meter reads exactly 100V when the DVM reads 100V; the meter reads 120V when the DVM reads 121.9V.
I connected a 100-Watt incadescent lamp to the test configuration above and the meter indicated 84W at 120VAC as shown below.
The current (Amps) indicated lower than expected as shown below. I suspect the meter is inaccurate as such a low reading.
Below is a section of a 1951 Simpson sales brochure describing the Model 390 Volt-Amp-Wattmeter. Note the dealer's net price for the instrument was $39.50 and the carrying case was $5.50 in 1951.
Below is a picture of the leatherette-covered carrying case.
