# Coils values

Discussion in 'General Electronics Chat' started by Gdrumm, Feb 25, 2014.

1. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
Yet another old meter, a General ElectriC Model 8AP9VASA1, this one has a stamp inside that says US Navy , and a piece of paper with typeing that says November 13, 1945 Standard Meter 600 volts / 595 volts.

It didn't work, and when I took it apart, I found 8 coils, wired in series.
Each coil appears to have a number written on the top. (several are illegible). When I added the numbers together, my best guess is that their combined value is around 25,000.

Three of them tested bad, and one (of the original 9) was missing.

I took one of the bad ones out of the circuit, and with some drilling of a rivet, was able to get it disassembled on one end.

One of the small wires had broken off, and I can't find the loose end that is still attached to the coil. They all appear to be wound by hand.

Is there a way I can use modern off the shelf coils in series to recreate what was originally done?

If not, how can I more accurately measure the value of each coil, and guess the values of the unknowns?

It's a nice looking old meter, and I would like to get it working if possiible.

I've never wound a coil before, but looks very time consuming.

Any insights are greatly appreciated.

Thanks,
Gary

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Last edited: Feb 25, 2014
2. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
I bypassed the known bad coils, and measured the remaining 6 in series,
It added up to 31,39 K. If divided by 6, and multiplied by 9, then 54 K would have (could have) been the original. Does that sound plausable?

When I applied 110v, the needle did move slightly, and since the meter face goes from 0- to -600v, I would say the needle moved significantly, but not 110v worth.

So apparently the missing coils do make a difference.

My question is how to get it working properly.

I can experiment (I have numerous coils I've salvaged) but thought it best to ask you guys first.

Does anyone know of an adhesive that will work on Bakelite?

Thanks,
Gary

Last edited: Feb 25, 2014
3. ### jmoffat Member

Jul 18, 2012
41
1
Those coils are likely to be precision resistors. Look at the face of the meter. At the bottom in fine print it should say something like 20,000$\Omega$/volt. This is a clue to the meter sensitivity. With this info you can calculate the resistance values needed to make your meter work properly. My guess is that your meter has a 50 microamp movement.

4. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
jmoffat,
Thanks for the reply.

The fine print says Resis of 600 volt circuit 102210 oms 600 volts cycles 25-125.

Can I replace the missing coils with resistors to bring it up to that value?

I have measurements for each of the good coils, and many resistors of various values.

Thanks

5. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
Any other ideas?
Thanks

6. ### Gdrumm Thread Starter Distinguished Member

Aug 29, 2008
684
36
Well,
Since I can only measure up to 110 at my house, I decided to put two resistors in line, to bring the overall ohms up to 109K,

I'm guessing that at higher voltages, heat might be a problem, but I doubt I'll ever use it.

I did attach a note (taped inside the flip up cover that exposes the dial) in the event someone in the future wants to deal with it.

Thanks for looking, and thanks jmoffat.

Gary

Last edited: Feb 26, 2014