I have a trash picked 220 that is in great condition and seems to work fine, other than a damaged triax connector that I replaced very carefully following another thread on this forum. Just playing with it, I noticed something that I can't explain. If I connect the output (center pin and inner shield) directly to my ammeter, the output is nearly right on. From 1uA to several 10s of mA it's very close. Down to 100nA also seems ok, and maybe 10nA too but that stretches the capability of my AM-140A.
I thought I'd try a 1M resistor on the output, and at 1uA output that should measure 1V out, right? Well I know Ohm's law and 1V is what it should be. But the 220 isn't mustering any more than about 0.7V, and at 10uA it's only getting about 3V out. I've measured the 1M resistor, and measured the current using the meter, and it's simply not generating enough voltage to reach the current output. V-LIMIT is set to 5V, but increasing to even 20V makes no difference.
At the other extreme, using a 100 ohm, I see around 10V for 100mA and 0.01V for 100uA, which seems right.
I don't believe I'm exceeding any specifications. What am I doing wrong, or is there something wrong with this thing?