I will test something else: a full-wave rectifier and a 200µA meter.
It will work, with a bit of luck, but 4 Ge or schottky will be required, because two drops of ordinary diodes will not be tolerated.
It will work, with a bit of luck, but 4 Ge or schottky will be required, because two drops of ordinary diodes will not be tolerated.
I found another two VU meters, from an old tube reel recorder.
They are the same 200µA. However, when I drop the resistor to 47K ohms, I get a full scale deflection.
Now I will get some small Schottky diodes and a few caps...
They are the same 200µA. However, when I drop the resistor to 47K ohms, I get a full scale deflection.
Now I will get some small Schottky diodes and a few caps...
Don't forget that Ge "crystal" diodes are also suitable (and even better than most schottky's) and could be easier to salvage from old equipments.
They include many two-digits 1N types, like 1N34, 1N70, european types, OA90 to 95, AA119, 143, etc, plus japanese 1Sxx, soviet types, etc
They include many two-digits 1N types, like 1N34, 1N70, european types, OA90 to 95, AA119, 143, etc, plus japanese 1Sxx, soviet types, etc
"ALL" VU meters are 200uA. Unless they are very cheap 1mA units with a custom driver.
Needle-type VOMs come in $10 500uA and $50 50uA basic movement.
This one is 50uA for $33, and you don't even have to open it up.
https://www.amazon.com/Tekpower-TP7244L-7-Function-Multimeter-Protective/dp/B00MI6T0IW
(Oddly, it says 60uA on the switch?)
Another key clue is the fine print on the scale: "2K/V" is 500uA, "20K/V" is 50uA. If they don't actually expose a 50uA range on the switch, you can bust it open and connect direct to the movement.
This appears to also be a 50uA meter:
https://www.amazon.com/Tekpower-TP8250-Multimeter-Variation-Measurement/dp/B00SLVPJSI
Needle-type VOMs come in $10 500uA and $50 50uA basic movement.
This one is 50uA for $33, and you don't even have to open it up.
https://www.amazon.com/Tekpower-TP7244L-7-Function-Multimeter-Protective/dp/B00MI6T0IW
(Oddly, it says 60uA on the switch?)
Another key clue is the fine print on the scale: "2K/V" is 500uA, "20K/V" is 50uA. If they don't actually expose a 50uA range on the switch, you can bust it open and connect direct to the movement.
This appears to also be a 50uA meter:
https://www.amazon.com/Tekpower-TP8250-Multimeter-Variation-Measurement/dp/B00SLVPJSI
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