Effect of transit time:

There are two effects:

          1)  At  low  frequencies,  the  grid  and  anode  signals  are  no  longer  180 phase, thus causing design problems with feedback in oscillators.

          2)  The  grid  begins  to  take  power  from  the  driving  source  and  the  power  is

          absorbed even when the grid is negatively biased.