The origin of these three
meters is not known. "Philip Harris Ltd", (whom I'm
reliably informed, by Peter Raven, was a Birmingham-based supplier
of scientific instruments and apparatus to schools and laboratories
up to at least the mid 50s) is stamped on the base and "British
Make" is printed on the faces of the two on the wooden plinths,
whilst "British Made" is printed on the smaller test
meter. All meters are finished in bright nickel plating and all
three are completely undamped and are of the "Moving Iron"
type which are inefficient but can measure AC as well as DC without
the need for a rectifier.
I don't think the wooden stands
and the meters started life together as, if you look carefully,
you can see a shadow of a larger meter around the peripheries.
There are also screw holes in the wood for slightly larger meters.
The two meters with the side connections look 1925 or earlier
whilst the one with the cord looks typical of the meters used
by constructors of radios in the 20s and 30s. Between 1925 and
1934 valve heaters were lit by 2 volts DC or 4 volts AC, thus
the meter would be just right for this purpose. Later 6.3 volts
was used and this would clearly be too high for the meter. Earlier
you would have not encountered many filament voltages higher