Dave,
   
  One must have the utmost respect for 15,000 volts !!!  The basic rule with 
high voltage is always keep one hand in your back pocket and then turn off the 
power BEFORE any adjustments or measurements.
   
  If you are referring to the microwave power supply (3,500 v no load) the same 
rules apply but once the power is on the cell voltage drops to about 500 v and 
continues on down to as low as 100 volts.
   
  Yes I use a PWT.
   
  As stated the initial current is the determining factor as to the length of 
the brew cycle.
  The initial current is a function of the conductivity of the DW. If you buy a 
large quantity of DW and hold it at normal room temperature the conductivity 
will slowly increase.
   
  I work at about 68 deg F. in my basement. It adds stability to the DW.
   
  If you shut off the system at the same current density then PPM's will be 
very close.
   
  Does that answer your questions?
   
  "Ole Bob"