In article .com,
"terryS" wrote:

Thanks Chris and others. Part of what I was wondering is a seemingly
'dud' RF ammeter. The movement might be OK and could be, say, 1 or 5
milliamp etc. fsd.


Ah, right. In that case:

The ex-RAF meters (marked A (crown) M for Air Ministry) have the resistance
wire soldered directly to the back of the terminals on the case. The
thermocouple is then spotwelded to the middle of the resistance wire,
and one lead goes to one side of the movement directly, the other goes
via a "coil spring" of nichrome resistance wire (length cut to get the
thermocouple calibration correct) to the other side of the movement.

If it's open circuit across the terminals, then the resistance element
has blown. The thermocouple and movement should still be perfectly OK.

(I've considered trying to replace the resistance wire but calibrating
it will be the difficult part.)

Somewhere I have a box of dead meters....

I may be some time.

Chris.

--
Most uses of "spider" have noninsect meanings. -- Christine Malcom-Dept.