Re: Simpson 260 repair

bitrex <user@example.net> wrote:

On 4/4/2025 12:56 PM, Joe Gwinn wrote:

On Fri, 4 Apr 2025 11:36:40 -0400, bitrex <user@example.net> 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

 
Leave this alone - it's normal for such meters.  The 260 may need to
be calibrated.
 
Joe

 
Right. I've calibrated the DC voltage as best I can with what I have;
get the meter as close to full scale at 50 uA into it as I can with the
parallel pot, then set voltage across the meter movement and its series
pot to 250 mV. On the higher voltage ranges (which is what I'd tend to
use it for anyway) it definitely seems good enough for rock & roll.
 
Anything further with analog meters I believe require specialized tools
which I ain't got.

Sometimes there is a magnetic shunt which is used to set the sensitivity
of the basic movement.  If the magnet has aged, the shunt may need
adjusting.


--
~ Liz Tuddenham ~
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