Calculate the appropriate bias voltage (and resistor) of a condenser microphone
There is really no way to non-destructively determine the maximum bias voltage the mic can take.  If it really is a condenser mic, not electret (which are driven similarly), then up to 10 V is almost certainly safe.  2 V is safe for just about any kind of mic that requires a bias voltage.  You can start there and see what it sounds like.  If the signal is too weak and buried in noise, crank up the bias voltage.

Look around for similar-looking models and see what bias voltages they require.  Some old condenser mics used up to 100 V back in the tube days.  Less voltage doesn't hurt the mic, but you get lower signal to noise ratio.  Too high a voltage and something will arc, probably causing permanent damage.