(Early) Avometer rotary selector detents

[The Philpott]

As a lot of Avometer problems relate to moving parts i thought i would revisit mushy rotary selectors on a Model D dating from 1945. It turned out that the DC selector spring had a free height insufficient to engage with the knob detents- it was around 6mm (and needed to be of the order of 7 or 7.3mm) but bearing in mind the variance in (and hand-finished nature of) the meters these measurements cannot be relied upon- so here's the photographs which should get you closer to where the spring needs to sit-

1- too low
2- spot on- just marginally below the facia.

Note that the phosphor bronze ball will make a bid for freedom at the earliest opportunity during dismantlement..

Also note that on the Model D getting to the DC assy. means that the high voltage shunts have to be removed, then the small resistance reference board underneath.

(On the AC selector the mushyness was not as bad- and was simply down to a mixture of grease and dirt gunging up the action.)

Some of the locking pins which secure the knob/shaft assy. to the die cast rotor lacked a chamfer on the ends- this can make them very difficult to reinsert. When this happens i swap it for a chamfered spare, or spin the offending pin in a drill and dress the ends. Note also the pins are ferrous and can get sucked onto the magnet.

This meter arrived a few years ago minus all 8 casing screws and with an light internal coating of dust- and due to it's feeble readings was the subject of my first experiment with a Neodymium booster magnet- the improved readings have held up to this day to within two-thirds of 1% of FSD (ie one 'notch' or less on the outer scale) - so i am leaving it alone!

The pencil markings inside indicate this meter survived two factory interventions in 1951 and 1957- which may or may not explain why a rogue detent spring was used.

Dave