Many gaz filled rectifiers and some high vaccum types cannot withstand
heavy start up currents. Furthermore, as previopus formula show,
output voltage 
is widely influenced by load characteristics in
the case of capacitive loading : when designing a class B amplifier,
whose dynamic impedance is dependent on output power level, capacitive
loading can yield to unacceptably high mean voltage varaiations. In
those cases, inductive loading can be the best answer.
Computation of the inductance L that is wired in serie with the load
is done by considering hum current 
flowing thru it : if it is
higher than mean current 
, a part of the cycle will exhibit
current reversal, which must be avoided. This condition on will
put a minimum value on L. Let us note first tha mean value of
voltage before the coil is :
Where 
is the so-called arc voltage, non zero if a gaz filled
diode is used. In the following, we will assume 
for easy
writing of formula : if needed, it can be taken into account
easely. Using the expression of shirt-circuit current, previous
formula becomes :
Hum voltage in the case of an inductive loading is the one that would
have been obtained with an unloaded rectifier. We can assume, with a
fairly good approximation, that this voltage is a complete sine wave
with amplitude :
Formula giving amplitude 
of fundamental wave can be used here,
taking 
as opening angle. In the case of a biphased
rectifying, we have for example :
Amplitude of alternating current thru the self is then :
If one wants that current never vanishes, this last value must be no
higher than , which yield to :
or equivalently, using 
:
For a 50Hz mains, this can be writtent :
With the same computation, and for a triphased rectifying, one has :
and in the hexaphased case :
It can be noted the interest of using haxaphased current when working
with an inductive load!
Computation of RMS current at transformer secundary is difficult
than with a capacitive loading. It is possible yet to admit that with
high values of self, current is nearly a rectangular wave, yielding :
