If I connect collector to +50V Vcc and ground base, what will be the voltage
on unconnected emitter?
My multimer has input resistance of 1MOhm (when voltmeter) and it
measures 2-12 volts.
This is even more of a problem with darlingtons.
I'm guessing this is because of leakage from c to e so I put 10k between e and gnd
and it works.
Am I correct and what is the best way to solve this problem?
Yes, all transistors and diodes have a small amount of leakage across a reverse-biased junction. A resistor of the correct size will absorb the leakage with only a small voltage drop across the resistor.
But why are you concerned about the voltage on an open emitter?
I (tried) to make most basic voltage regulator (zener+emitter follower) but I had to use darlington (for higher current),
so I had to solve this problem that it gives some voltage on it's output when it's meant to give 0V.
So I am asking where is best to put this grounding resistor(s) (and what would be the values) given I am using discrete darlington.
Edit:
Also now I am interested what would be the answer if it was academic concern.
It's a good idea to have some load on the output anyway. Even a 1 megohm resistor might do it. If it is a darlington, then a resistor from the second base to ground is also a good idea if you really (for some reason) need some very low output. Some darlingtons have a built in resistor from second base to second emitter though.
The only reason i can think of for needed this is when you disconnect the load entirely so that there is no load connected. With a fixed permanent resistor from emitter to ground this should no longer be a problem.
I (tried) to make most basic voltage regulator (zener+emitter follower) but I had to use darlington (for higher current),
so I had to solve this problem that it gives some voltage on it's output when it's meant to give 0V.
So I am asking where is best to put this grounding resistor(s) (and what would be the values) given I am using discrete darlington.
Edit:
Also now I am interested what would be the answer if it was academic concern.
Now that you've told us your application, I understand your concern.
Yes a resistor to ground should solve you problem. A value of 1k-10kΩ from the emitter to ground should suffice. If that's not sufficient for a Darlington, then go to a lower resistor value, but no lower than needed.
By academic, I meant whether it was only of concern from a theoretical point of view, and not a practical one. But you have a practical concern.