Avominor (Universal) movement/s notes

[The Philpott]

As i have not yet had to adjust the play in pivots yet, i confine myself to comments on:

1- The balance of the movement
2- The adjustment of the magnetic shunt due to ageing.

The subject of the photo is a Model 2, which is more time-consuming to service due to the extra resistor board fixed behind the movement. This meter does not have a compartment for leads due to the extra components within.

For some reason this meter tends to suffer with the tail-weight being too heavy, one can only guess as to why this is, although if you are dealing with a needle that has lost it's red 'fly speck' then this would throw it tail-heavy.

Best acronym i could find in my spares box for balancing a movement is ZITS-

Zero (internal >>) Tail, Side.

The medium used in the photo for compensating the tail-heaviness is an acrylic car touch-up pen (with a cocktail stick.) The drying time is not too short, and as the solvents evaporate the 'bead' can be added in more than one stage- add, allow to dry, check, add, allow to dry, check etc. The position of this bead is critical as it is possible to foul the Z stirrup or the rotating magnetic shunt if you place the bead any lower down. I was able to make the bead very small as it is a long way up the needle.

This meter was showing 18% deflection in the 'check' position before tail balancing and 3% afterwards, which is (almost) as good as you are going to get. This job should be a little easier with a less sensitive Model 1, but these meters do not seem to go out of balance very much anyway.

The magnetic shunt is a very fine tuning device and if you need to try for much more than 3 or 3.5% increase you are likely to foul the shunt on either the needle or on the rear resistor board. Needless to say ferrous spanner/s should not touch the magnet proper.

Even if the reference resistors are totally accurate there is an additional issue to bear in mind; this particular meter needle can be accurate at 80% FSD but lag behind slightly at, say, 30% FSD. If in doubt go for accuracy at higher readings of 70 or 80% as this is the best compromise. (in my opinion)

While you are inside an old unloved Model 2 it is very worthwhile to clean the 'Zero ohms' spindle and the bronze leaf which presses on it. You may regret it if you reassemble and neglect to do this; the ohms range won't work very well.

The arms at the extreme rear of the movement (where the hairspring attaches) may need to be gently tweaked around so that the Z peg is at the centre of it's adjustment range, with the needle sitting at a perfect 'zero'

Best of British!

Dave

[The Philpott]

On both cases where i did this job on a Model 2 i replaced the wires going to the resistor pack with slightly more flexible ones, as i had problems with fatigue of the single copper cores.

[Phil G4SPZ]

On the handful of occasions when I've had to rebalance a (full-size) Avo movement, I've used clear nail varnish. It dries pretty quickly.

[The Philpott]

On the first 'minor i used araldite- which dried TOO quickly for comfort!

On a full size movement where virtually all the weights had corroded away i had to use copper wire on the tail- with paint to secure it. Paint alone wasn't heavy enough.