16.07-4: Amprobe 1955 Clamp-On Ammeter and Voltmeter

HHCC Accession No. 2006.212HHCC Classification Code: 16.07-4

A portable, induction type, clamp-on, analogue ammeter and voltmeter in hansom, now well used, black leather case with spring clip. Reflecting a new generation of HVACR test equipment emerging in the 1950’s, it measured current on 6 scales from 6 to 300 amps, and voltage on three scales from 150 to 600 volts, Amprobe, circa 1955

Image Gallery (2 Images)

16.07 Electric Motors - Installation, Test and Repair




Pyramid Instrument\ Corp, New York



Serial No.:



4 x 9 x 2 inch h.

  1. 3 Lb.



Exhibit, education, and research quality, illustrating clamp-on, induction type, portable, analogue test and electrical measurement equipment used by HVACR mechanics starting in the last half of the 20th century

Patent Date/Number:

From York County (York Region) Ontario, once rich agricultural hinterlands, attracting early settlement in the last years of the 18th century. Located on the north slopes of the Oak Ridges Moraine, within 20 miles of Toronto, the County would also attract early ex-urban development, to become a wealthy market place for the emerging household and consumer technologies of the early and mid 20th century.

This artifact was discovered in the 1950’s in the used stock of T. H. Oliver, Refrigeration and Electric Sales and Service, Aurora, Ontario, an early worker in the field of agricultural, industrial and consumer technology.

Type and Design:

Clamp-on, analogue, indicating ammeter, with test cables for measurement of line voltage, iron-vane/electrodynamometer metering [See Reference 1]


Black Bakelite style, robust body with heavy, protective, black leather, fitted carry case

Special Features:
Performance Characteristics:
Control and Regulation:
Targeted Market Segment:
Consumer Acceptance:
Market Price:
Technological Significance:

This clamp-on, induction type, analogue meter tells many stories of its time: The increasing sophistication of test and measurement equipment used by HVACR field workers starting in the 1950’s, The transition from traditional, bench type, delicate electric test equipment [See 16.07-2] to more rugged portable equipment, more convenient and user friendly. The increasing sophistication and complexity of 20th century HVACR technology applications and the accompanying need for better indicating and recording instrumentation required for equipment installation, performance monitoring, trouble-shooting and diagnosis.

Industrial Significance:

In the early post W.W.II years, it became increasingly evident that the HVACR industry was seriously limited by the lack of rugged, affordable test and measurement equipment for field use in installation and after market service. The field was clearly dependent on manufacturers who would design, develop and bring such equipment to market, at a price the tradesmen could afford. Often the equipment that was commercially available was of the laboratory type, too sensitive and delicate, lacking the robust quality needed for life in the toolbox.
This induction, clamp-on meter, while it represented a truly remarkable advance in electrical load measurement required by HVACR field technicians, would at the same time mark the end of the generation of analogue instrumentation. For the era of the direct, digital read out instrument was at hand.

Socio-economic Significance:

It was the 1950’s and Canada’s was growing rapidly. The mechanical and electric trades were a major part of that new culture. The home service trades grew rapidly during this pre W.W.II period and on into the 1950’s, plumber, electrician, heating and refrigeration. They brought with them a new quite different breed of industrial worker, mobile, entrepreneurial, and skilled in the new consumer technologies, then available for the Canadian home.

Socio-cultural Significance:

G. Leslie Oliver, The T. H. Oliver HVACR Collection

HHCC Storage Location:
Bibliographic References:

The theory and practice of analogue electrical measurement, reflecting the technology of the early post world war years, was set out by Robert Ward Page ‘Introduction to Electrical Engineering’, Chapter V, Prentice Hall, 1947.


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