Andrew Holland - Business manager
Production has recently ceased of the very last model of analogue AVO meters, the Model 8 mk7. This was a true British icon that could trace its roots directly to one of the twentieth century’s most significant breakthroughs in instrument technology.
A brief history...
The first AVO was born out of the dissatisfaction of Post Office engineer Donald Macadie with having to carry many separate instruments with him as he went about his daily work. It occurred to him that he could ease this problem by integrating the functions of several instruments into one.
Macadie took his idea to the Automatic Coil Winder and Electrical Equipment Company, where it was translated into reality. The first AVO – so named because it could measure Amps, Volts and Ohms – was put on sale in 1923. This was a DConly instrument, but it’s a tribute to the foresight of its designers that many of its features remained unaltered right through to the last Model 8.
From this point on, the AVO meter went through many developments. In 1933, for example, the Universal model was introduced that added AC measurement capabilities, while 1936 saw the introduction of the Model 7 with its exceptional – for the time –1,000 ohm per volt DC sensitivity. The Model 7 incorporated not only a fuse, but also a new form of overload trip designed to protect the instrument if the pointer banged against the end stop of the scale.
One of the biggest developments came in 1952 with the launch of the very first AVO Model 8. Designed to meet the needs of the rapidly expanding electronics industry, this offered a sensitivity of 20,000 ohms per volt on DC ranges – a figure previously unheard of outside the laboratory. At last it made possible meaningful readings on the high impedance circuits that are so common in electronic apparatus.
The Model 8 was exceptionally successful and played a big role in allowing AVO, as it was by then known, to deliver its millionth multimeter in 1966. As the 1970s approached, however, it was time to move forward and October 1972 saw the launch, with much fanfare, of the AVO Model 8 Mk V. Outwardly very similar to the early versions of the Model 8, internally this was a completely different instrument.
Megger continued production until 2008, when it became impossible to purchase some of the components, and the product had to be withdrawn.
Megger will be offering repair and calibration services on the Mk 7 models for years to come.