Hello Klaus, I think he wants it the other way round- define an exact resistor value as substitute for the mic.
This is - IMO - the best way doing it, it keeps you from frying an valuable mic.
For the AC701 type mic's it might be different from type to type, e.g. KM56:
Filament: 100mA @ 4V makes 40 Ohms / 0.4W (use 2W resistor or burn your fingers).
Anode: 0.61 to 0.53mA @ 120V makes 197 to 227 kOhms / 0.06W
(choose 200kOhms / 0,6W).
For the U47 it's simple:
40,5 mA (heater + anode supply) @ 105V makes 2590 Ohms / 5W
I suggest 1K2 + 1K4 Ohms /5W in series, so they don't get too hot.
For testing AC701-type PSU's remember to load both filament and anode supply, as the voltage drop inside the transformer will change if you only load one of those.
This is for fixing faulty supplies, not for calibrating them to a certain mic!
It seems that specially the heater voltage of AC701 mics need to be carefully calibrated to gain long tube life.
Have a scope and at least 1 electronic multimeter handy for faultfinding.
Monitor your line-supply voltage, if it's far off specs don't expect the PSU voltages to be in specs.
Check the ripple right after the rectifier - it shouldn't be too big, and it should be 120 (100) Hz.
If it's 60 (50) Hz one leg of the rectifier is blown.
If it's too strong, the 1st capacitor is dried out or blown.
Kind regards
Kai