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Old 7th Mar 2008, 2:02 pm   #276
pmmunro
Octode
 
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,797
Default Re: AVO Multimeter survey

The PF sockets on your 1978 Model 40 are for connection to the optional Power Factor Unit described in the Model 40 manual (and very seldom used, I would guess).

You state that you have refixed the plastic window - surely it should be glass?

The trouble with a plastic window is that it can attract a static charge and that will affect the long knife-edge poiter of an Avometer - in effect a combination of moving coil instrument with electrostatic error source.

There was a thread a few weeks ago about refixing meter glasses - my own preference is for one of the modern specialist epoxy adhesives designed to fix glass as I assume that it accommodates differential thermal expansion amongst its merits. In default of a spare glass, it should not be too difficult to get a local glazier to cut you one to match a pattern - the plastic replacement of a stiff card.

Essentially this meter is a direct development of your 1937 meter using a block magnet movement instead of the horseshoe magnet type, a cut-out instead of the fuse, improved switch design and component resistors instead of wound coil resistors.

Of these features, most are improvements but the type of resistor is debatable. The wire coils are more stable but very delicate, as you have found, and expensive to produce. The component resistors do sometimes drift but are much easier to handle without damage.

PMM.
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