accurate instruments model 257 tube tester dial value
 

I have a accurate instruments model 257 tube tester that has I dial that the needle and tension spring need replaced, I am planning on replacing the dial with one of identical electrical value, however I cannot seem to find the dial value on the schematic. Does anyone know the value of the dial/ how to replace the tension spring and the needle and where to find a needle and tension spring? Any help would be appreciated.

Good luck. If anything, while you have the tester still together, put a voltmeter across the meter and measure voltages in operation. Primarily when the instrument is going to have a known reading. Such as filament voltage, or line calibration.

If I had to guess, I'd say the meter is basically a DC voltmeter, but I'm only guessing.

Funny enough, my mother used to rebuild meter movements for the Simpson meter company. Of course that was ages ago. I honestly doubt you'll be able to find any meter parts now... hell you probably couldn't find them then.

Are you absolutely certain the meter is kaput? Maybe a drop of oil would fix it. Other than that, I can only assume this instrument has a lot of miles on it.

Why do you think you need to replace the needle and spring?
What is the basic problem?
If the meter is functional there are tests you can do to determine the meter characteristics.

The reason they need they need replaced is because the needle is snapped and the spring..... well you know what happens when Slinkys get all tangled? Imagen that but on a tension spring

Is the coil in the meter still functioning, and is there any damage to it of the bearing surfaces?

Is the plastic lens covering the meter intact?

The spring could be replaced from a meter of comparable size. It's anchored at the center pin and the other end connects to base of the meter usually through a wedge pin. On the face of the meter there's a spreader that the spring is fed through for meter adjustment.

The needle could be made out out of some very fine wire or brass shim stock and shaped.

I have repaired them before and it's a bit of trial and error getting them right, but it can be done.

One of comparable size in a Multimeter, VTVM or a old CRT tester might work.
Just check the resistance of the coil between the replacement and the original.


Is there any markings on the back of the meter like 50, 100, 200 uA?

Is the coil in the meter still functioning, and is there any damage to it of the bearing surfaces?
Yes, it works, Nothing other then the dial and spring are broken
Is the plastic lens covering the meter intact?
Cracked, small piece missing but otherwise fine
The spring could be replaced from a meter of comparable size. It's anchored at the center pin and the other end connects to base of the meter usually through a wedge pin. On the face of the meter there's a spreader that the spring is fed through for meter adjustment.
Oh ok, Thank you however I would likely need a diagram on how to thread it like with the spereader.
The needle could be made out out of some very fine wire or brass shim stock and shaped.
*Of note some things had to be deleted due to text size
One of comparable size in a Multimeter, VTVM or a old CRT tester might work.
Are there any markings on the back of the meter like 50, 100, 200 uA?
Not to my knowledge.

How would I find the spring?

Like possibly not from another meter

Yeah another meter is likely your best bet. It would have to be a fairly large meter to have a spring large enough bring the needle back to zero each time.

If the original spring is just bent up you could work the bends out with tweezers on either sides of the bends. They can be a bit bent and look like crap but still work fine as long as the spring isn't binding on anything or rubbing against itself.

Ok thanks

Yeah the old meters dial barely moves without the spring so it likely needs replaced. You test the ohmage then get a dial of similar value right? Also you test the ohm value by removing the coil from the circuit then testing the coils value right? Thank you for all the help you have given me so far.

Yeah just disconnect the leads and measure.

So the spring is totally gone frome the original meter?

yes, it could be re added but the meters movements are so bad that it is not worth it to try and repair it.