AVO Model D
(
Testmeter Type D Ref 10/S 10610)

ser no 21272-845

The Admiralty and the Air Ministry procured many thousands of AVOmeters during WW2. These were substantially the same as the commercial instruments of the time, but modified to suit their particular requirements. The  model D was a variant of the model 40 which was introduced in 1939/40 except that that it did not contain the two 4.5 volt batteries used for the the highest resistance range and had diferent voltage and current ranges. The Q knob has been retained but is non functional and the divide by 2 button of the model 40 has been replaced with a switch K=1 K=2. This meter does not have the more usual AM and crown logo at the top of the scaleplate.

By 1965, the company had already created over one million AVOmeters. The firm also produced a range of smaller multimeters, the AVO Minor and later the AVO Multiminor as well as a number of special instruments such as the Heavy Duty model. Production of the iconic model 8 meter ceased in 2008. Though known for their Avometer general purpose multimeters, they made a wide range of test gear including valve testers, oscillators and light meters. You will find more information here about these instruments and other similar models. AVO also produced a range of smaller multimeters which are described here.

modelD

Avometer model D ser no 21272-845 in Bakelite case

This belonged to the late uncle of Imogen Radford. He was a collector and hoarder of all sorts of things, and while she was helping her aunt with clearing out her house she thought this might be of interest. It was in excellent condition and complete with cloth covered leads, prods and clips and a nice leather caase. She thought his national service in the Royal Air Force, might have prompted him to buy it. I made a donation to the charity she had been doing a sponsored swim for.

modelDmodel D

As with all avometers an abbreviated set of instructions can be found on the underside             

  
avo leads

The leads for early meters were cloth covered like these

Batteries The model D used a rectangular 1.5 volt cell with a brass terminal and a flying lead for the negative connection this can be replaced with a single cell size D with soldered connections.

How old is it? Many AVO meters can be dated from the last 3 or 4 digits of the serial number under the right hand end of the scale. These define the month and year of manufacture. For example this one was made in August 1945.

What is it worth? One in this condition with leads, probes and case is unusual so maybe 20. The model 8 being more sensitive is probably a better investment, you should be able to buy a model 8 MkII for 10- 20 which you will find equally as good as the later models though without leads and probes.