Re: Simpson 260 repair

On 4/9/2025 7:42 PM, Cursitor Doom wrote:

On Fri, 04 Apr 2025 18:01:17 +0100, Cursitor Doom <cd@notformail.com>
wrote:
 

On Fri, 4 Apr 2025 11:43:22 -0400, bitrex <user@example.net> wrote:
>

On 4/4/2025 11:36 AM, 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

>
Oops, I meant to post this in sci.electronics.repair but here we are.

>
I did wonder! Simpsons are nice meters. Really nice and broadly the
equivalent of the UK AVO brand (still in business AFAIK). I really
like these old analogue meters. People say stuff like 'well, the
trouble with them is they load a circuit too much compared to modern
DVMS' but that *can* be desirable in many cases. Repairing vintage
radios you find that oftentimes the servicing instructions have
voltages printed on them which were read by meters with 20k ohms/volt
or less, so at high impedance parts of the circuit a modern DVM will
give completely wrong readings. Also I find it's much easier to peak
signals with a moving coil meter than a DVM. And another thing - you
want to monitor a voltage constantly over days and weeks (or a
current) you can do this with an analogue meter without having to
worry about the battery draining. And when reading high currents,
there's no time limit like you find with modern DVMs. You can leave it
hooked up to 10 or 12 amps for as long as you like.
I could go on, but there's just a few of the reasons I like these old
beasts.

 Turned up trumps again today. Checking the DC tuning voltage to a VCO.
It was supposed to ramp up from 2.5V to 10V reset and repeat over a 3
second cycle continuously. A DVM failed to reveal this control voltage
was misbehaving badly, but it was  *immediately* apparent with an
analog meter.
Sometimes, you just can't beat 'em.

Nice, I'm happy mine's working pretty well now.
I think I'll hold onto it to barter for a Cadillac with once Trump's finished turning dollars to toilet paper..