taut band meter movement repair

[Andyb1234]

Hi ALL,
I have a AWA G231 audio osc with a faulty meter . I think it is a taut band meter movement as the movement is suspended by a thin wire between two points. I have fixed it once but the wire has broken again and now is too short.

Has anyone any information on sourcing about 5cm of this wire or a possible substitute.
Cheers Andy

[Kleinstein]

From the looks the meter movement is driven by some amplifier and likely with a series resistor to convert a voltage to current. So it would not be that bad when the sensitivity would change. Sensitive movements may have a thin ribbon instead of the wire (gives better ratio of  tensile strength to torsional spring constant). I don't expect this here.
The restoring force goes up quite fast ( AFAIK 3rd power of the diameter or width times thichness squared for a ribbon) and the replacement should thus not be much thicker. Flattening the wire would be a last resort.

So one could get away with a different, easy to solder and hard (to avoid drift of the zero) and ideally non magnetic thin wire.  The main alloys in mind would be brass and bronce (e.g. manganin).
Pure copper is a bit soft and likely not working (can cause drift of the zero) - maybe flattened to a ribbon or a pealed off PCB trace for more cross section.

[Andyb1234]

Hi Kleinstein
Thanks , you are correct it is a flat ribbon soldered at each end

[robert.rozee]

you could perhaps try the hairspring from an old mechanical clock or watch?


cheers,
rob   :-)

[floobydust]

I find vintage mention of Westinghouse taut-band wire 0.005"x0.005" for 1mA full scale deflection movements.
Then many meter manufacturers came up with their own special wire. I think you'd have to bridge the gap from an analog panel meter manufacturer and a wire manufacturer to find a source. Or get a same make/size meter as a parts donor.

The original panel meter is 100uA 2kΩ AWA 94771W52 Master Instruments and maybe ask them (if they still make panel meters i.e. Linesman's test set looks like they do) for a piece of wire, or look for other surplus equipment that uses the same style meter.