SKY 20 - S  Step-Up transformer.   This is a step up (pun intended) from the SKY 20 Step-Up transformer.  It is heavier and meatier than the SKY 20.  It has the same ratios (1:10 in LOW and 1:20 in HIGH).  If your system is very revealing, you will notice the difference.  It was hard to upgrade the SKY 20.  We tried many combinations and found that by increasing the length of the core, we could change the winding scheme just a bit.  You will "Hear the Magic."