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AVOMeter 8 MKV

December 29, 2013

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WIKIpedia has this to say about AVO multimeters:
“AVO multimeters were almost ubiquitous in British manufacturing and service industry, research and development and higher and further education. They were also widely used by utilities, government agencies and the British armed forces. A number of special versions were produced to British Admiralty and Air Ministry specifications and for other customers. The Model 8 Marks V, 6 & 7 were designed to meet a NATO specification and were standard issue to NATO services. Many commercial and military service manuals specified that values for measurements of current or voltage had been made with a Model 7 or Model 8 Avometer. Advertisements of the late 1930s compared the utility of the Avometer to the slide rule. Even nowadays it can still be found in regular use.”

SPECIFICATION
The manual states:
After repair the instrument should meet the following accuracies under reference conditions outlined in BS 89 1977 and IEC 51:
D.C. Voltage and Current Ranges: +/- 1% of f.s.d
A.C. Voltage and Current Ranges: +/- 2% of f.s.d. (50Hz)
Frequency Response: Variation from reading at 50Hz on ac current ranges or ac voltage ranges up to 300V not greater than +/- 3% between 15Hz and 15kHz.
Temeprature Effect” Variation due to temperature change not greater than 0.15%/C.

This polystyrene cased unit is a pale reflection of the older bakelite units I remember from my youth, especially the metal cased “Panclimatic” units that were made for tropical service. These had (as I remember) a brown bakelite top panel and a gorgeous brown hammer finish on the case. By this time, AVO was acquired by Thorn who (in my biased view) were the culprits in the demise of the quality of much of the British electronics industry. It also has plastic film wiring that must have reduced costs.
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I encountered two problems with it, one the meter was stuck and two there was an intermittent fault that I eventually traced to a cold solder joint. The stuck meter was due to the central magnet being loose and it had shifted, jamming the coil. I carefully re-centered it and used a little dab of varnish in suitable locations to fix it in place. I did not attempt to investigate exactly why it was loose.
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Here it is in the solid black leather case with the superb quality AVO test prods:
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3 Comments
  1. Lars Heineken permalink

    Thank you very much for the ineterresting read.
    It surprises me that the tropical units were equipped with metal cases. Unless they are rust proof, plastic would sounds like a better choice, at first .. Is there some background known about that that decision?

    • Hi Lars.
      The tropicalised units were intended for military service and I surmise that the metal cases were for toughness. They did not have polyxxx back then and bakelite while attractive, was brittle. The finish on the metal cases was superb and I doubt if rust would have been an issue. The British auto industry could have learnt something from that!

      • Lars Heineken permalink

        Thanks for the update. It’s probably easy to judge with the unit at hand.

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