It's not what it sounds like, and "Yes" I did plug it in.
I'm trying to build some calibration devices for . . . oddly enough, a Vacuum tube tester. (Yes. Vacuum tubes are still in use.)
The first problem is that the tester uses about 20 D'Arsonval meters. Not easy to find or get data sheets for. Some of these meters are 50 years old, so we don't want to blow them up, but they do need to be calibrated, daily. Unfortunately, that means that we need a variable current source that works between 100 pA and 500 mA. I know that you have all heard that you shouldn't test a D'Arsonval with a DMM. There's a good reason for that.
What I decided to do was buy some very expensive IC current limiters. But what do I do if they don't work as intended? I've been looking at low current transistors, of several types, but I haven't found any schematics that show something that appears to be worth pursuing. Sure, I could design a circuit to make a transistor that would do the job, but there are stability concerns. I don't understand the design parameters of stability circuitry that well.
Second problem is that I need a 0.5 VDC reference. Hmmm. Isn't that lower than the Vbeo? Yep. So where do I start looking? And voltage dividers are not the answer.
Do any of you work in this voltage/current range, or know someone else who does?
I've only been working on this for a month. A lot of that time was spent on Google. I haven't been able to even find a lead. It's frustrating.
In situations like this, in the past, it seems like the major problem was that I was barking up the wrong tree, but it's the only tree I can see.
I need new input.
BTW, I got perma-banned from another electronics forum for pursuing this search. Hope that doesn't happen here.
I'm trying to build some calibration devices for . . . oddly enough, a Vacuum tube tester. (Yes. Vacuum tubes are still in use.)
The first problem is that the tester uses about 20 D'Arsonval meters. Not easy to find or get data sheets for. Some of these meters are 50 years old, so we don't want to blow them up, but they do need to be calibrated, daily. Unfortunately, that means that we need a variable current source that works between 100 pA and 500 mA. I know that you have all heard that you shouldn't test a D'Arsonval with a DMM. There's a good reason for that.
What I decided to do was buy some very expensive IC current limiters. But what do I do if they don't work as intended? I've been looking at low current transistors, of several types, but I haven't found any schematics that show something that appears to be worth pursuing. Sure, I could design a circuit to make a transistor that would do the job, but there are stability concerns. I don't understand the design parameters of stability circuitry that well.
Second problem is that I need a 0.5 VDC reference. Hmmm. Isn't that lower than the Vbeo? Yep. So where do I start looking? And voltage dividers are not the answer.
Do any of you work in this voltage/current range, or know someone else who does?
I've only been working on this for a month. A lot of that time was spent on Google. I haven't been able to even find a lead. It's frustrating.
In situations like this, in the past, it seems like the major problem was that I was barking up the wrong tree, but it's the only tree I can see.
I need new input.
BTW, I got perma-banned from another electronics forum for pursuing this search. Hope that doesn't happen here.