[Boatanchors] d'arsonval meter question

[Brian Clarke]

Hi Ed,

That meter must be over 30 years old if it's a day. Permanent magnets lose their 
magnetism over time. They also lose because of very high temperatures, strong 
alternating magnetic fields and high level shocks - but the temperature required 
would have melted the remainder of the meter case, the magnetic field would 
have required a large amount of power and the level of shock required would have 
rendered your power supply unrecognisable. So, I reckon it's old father time.

Manufacturers of good d'Arsonval meter movements knew that and started with a 
stronger magnet than was required but put a movable shunt across the poles so 
you could adjust for that loss of magnetism and hence the apparent loss of 
sensitivity. It is quite possible that you could adjust that shunt to get the 
sensitivity back. I've done it - it's not difficult.

73 de Brian, VK2GCE.