2nd RCA WT-110T update

Yes the Shunt is inside the case directly across the meter terminals. (Carbon 5%) So I may have to disconnect it, then test the meter. It could be a 50uA meter and compensated for the voltage the tester uses to move the pointer?

Using a reference of 1 volt

If it's a 1uA meter then the volts per ohm would be: 1v/.000001 = 1Mohms per volt
If it's a 10uA meter then the volts per ohm would be: 1v/.00001 = 100Kohms per volt
If it's a 50uA meter then the volts per ohm would be: 1v/.00005 = 20Kohms per volt
if it's a 100uA meter then the volts per ohm would be: 1v/.0001 = 10Kohms per volt.

If it's a 1mA meter then the volts per ohm would be: 1v/.001 = 1000ohms per volt
If it's a 10mA meter then the volts per ohm would be: 1v/.01 =   100ohms per volt
If it's a 100mA meter then the volts per ohm would be: 1v/.10 =  10ohms per volt

So using ohms law E/R = 1V / 50uA =  20Kohms x 50uA = so to be safe use a pot at least 2x 20K = 40 K in series
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If the meter itself is truly a 100uA it would be 10Kohms and paralleling the shunt of 10Kohms the current would equal 5Kohms.

1 volt at 5Kohms would give a F.S. current of .5amps or 500mA

So in essence a 500 mA meter movement.
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If it actually is a 50uA movement, but made to operate as a 100uA then more calculations are in order.

Rs=10K Mr= 20K   10k x 20k = 200,000 and Rs + Mr = 30000   so 200,000/30,000 = 6,666.6 ohms

Now at 1 volt the F.S. is  E/ I   1/6,666.6 = .00015 or 150 uA

I guess I will have to remove the shunt to determine what is what. Other than that I'm going to put it on the back burner till I can get roundtooit.

Anything I'm not thinking correctly?

I am thinking that adding a 20K Ohm shunt resistor to the meter you got from VE1ARN will make it read 100uA full scale. Question: was that "Internal Shunt of 10K Ohms" you mentioned mounted on the back of the meter terminals, or was it inside the meter case? Either way, it should be possible to work it out so you'll end up with what the tester wants to see.
Rod

I forgot to mention, the meter movement itself has corrosion on the wire bobbin, both white and green. So It may not last. I'll test the meter for resistance using a power source and a couple of POTs. And after I do that I will spray some vinegar in the movement to neutralize any corrosion (even the magnet and center tube that the movement swings around) has, rinse with water then use ISO- Alcohol to draw any moisture out and allow drying.

If I get the Tube tester Which also has a lot of crud and corrosion cleaned then try to install another meter if the 50microamp movement won't work I'll plan on getting a new 100microamp meter and install the shunt and make one final attempt to get it working. Of course replacing all bad components like caps and resistors.

If that doesn't solve the units issues I'll toss the bugger out. And I will attempt to disassemble the old meter and see if I have the skill to at least get the meter to move smoothly.

Yesterday I was watching a Video on repairing a tube tester and it completely got me motivated to tackle my meter issue. Around 6:30 pm I finally decided to see how far  I could go to fix it. I removed it from the front plate again and disassembled the meter in stages, Bessel, dial plate, rear housing to the point of just the magnet-coil assembly. This was done in stages as in each stage I tried meter adjustments.

Those were to make sure the dial pointer wasn't dragging or touching the face plate dial. I would blow on the pointer and it was working at first smoothly from end to end. I started using my Microscope just to make sure of the clearance. Then as I moved the meter it started to hang up, so I knew someone had been tampering with the meter movement. The evidence was clear, the mounting nuts on the main tube tester panel had scratch marks around each nut.

The zero adjustment lever was way off to one side instead of being close to bottom center and it was bent sideways and down for what it should have been.
I tried to realign it so the slot would engage the face bezel zero screw to no avail as far as being able to zero the pointer. It just wouldn't zero.

Next I looked at the front spring and it was and it had become a squirrel cage. I adjusted the spring back into position so it was now a flat spiral Very tedious and time-consuming to say the least.

Then I tried to adjust the concentric space between each loop to make them, so the spiral wouldn't touch any part of the whole spring.
That didn't work in at all. The pointer was still wasn't zeroing and would continue to stick at several points.

Then I noticed several little flakes and steel or iron filings or wire hairs between the inner cylinder and gaps in the coil movement area. I had a hard time removing them with tweezers, so I resorted to using Scotch tape and a very and I mean very tiny knitting needle (not much larger than the head of a pin on the tip)

I even moistened the tip of the needle which really helped a lot.

Then still no progress. I think because of the internal corrosion it was just to far gone to be salvageable. ve1arn (Bob) sent me another meter of the same size out of a VTVM but the sensitivity was more. My meter was 100microamps and his was 50microamps. Boy that one cost me a lot in just shipping across from Canada. But it might be worth it though.

I assembled my meter back to gather and remounted it in place. I must note that it had an internal shunt of 10Kohms. Strange it even has to have one.
I will now have to adapt the new meter, and change face plates. Do the Math and experiment till the cows come home first.

The entire inside of the tube tester was filled with grunge which I will have to remove. And start testing resistors and caps before installing the new meter.

I need some time before I proceed as I am burned out on this project for now, so it's going to be on the shelf for a while whilst I am cleaning and further organizing my workroom.