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Old 18th Oct 2006, 4:38 pm   #142
pmmunro
Octode
 
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,797
Default Re: AVO Multimeter survey

Your description does not quite match a 48A. These were all made before 1948 as far as I know and at that time all full-size Avometers had horseshoe magnet movements.

What you describe sounds like a later movement with a block magnet from a Model 40. If that's the case it would explain the lack of a serial number. It could well be a legitimate repair but Avo or one of their official agents would usually transfer the serial number to the new scale plate.

If your movement has a block magnet, the slotted item on top of the magnet assembly is a magnetic shunt used to set the basic sensitivity of the movement.

Failure to zero may be caused by:

Movement out of balance - the pointer position should be within 1% of the set value whether the movement is horizontal or vertical in any palne;

Tangled hairsprings - with very careful use of a needle or similar these can be untangled by tracing gently from the centre outwards;

Sticking movement due to dirt, contamination, distortion of the pivots or damaged bearing jewels;

Looseness of one or both of the bearing locknuts.

Please see other threads on Avometer faultfinding and repair for more detail and some repairers who may be able to help.

Admiralty Pattern Avometers, 47A and 48A, are not uncommon on eBay and not usually very expensive but please try to find a good use for any parts, or someone who can use them as no new parts are available.

Peter M. Munro
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