Re: Simpson 260 repair

On 4/4/25 16:36, bitrex wrote:

Picked up a Simpson 260 6M at the local thrift store, I was initially disappointed to find it had a sticking meter but some gentle rocking freed it.
 Unfortunately the movement resistance is a little high, about 1880 ohms vs the 1800 in the service manual. This causes the movement to not fully deflect when 50 uA (sourced from an HP 6177B, and monitored by a recently lab-calibrated 3478A) is run through it, it goes to more like 48.5 out of 50.
 Is it correct that recharging the meter movement is the only thing that can help in this situation? It seems a relative error of 3% is actually still barely within factory spec so probably best to just let it go and enjoy a meter that's nice enough for the 10 bucks I paid for it, lol

Some meters have a magnetic shunt to account for the magnet strength
loss over the years. Not sure about Avo, but the uk GEC Selectest,
does have that and can be used to calibrate the meter. Only aware of
it because I bought a Selectest a while back, reading around 5%
low on all ranges, but was able to recal that using the shunt. Always
thought Selectest a better better than the Avo 8, but ymmv.
Rebuilt a 260 a year or so ago. Dated Dec 1944 and bought by my father
in the 1950's. Movement still good, but all over the place error
wise. Have done all the dc ranges, replacing just about all with
metal oxide, sometimes two or 3 in series to get the right value. The
5000 v range was especially tricky, but made a string in series, then
inside heat shrink to finish. used a resistance box to get the values,
then measure with dvm ohms for accuracy. Within a needles thickness
on most ranges now, a family heirloom and not bad for an 80+ year old
instrument.
Chris