A source of a.c. voltage is coupled through the output winding to the primary winding for inducing a.c. voltage signals in the secondary winding when {HEAD ~ d.c. control voltage} is applied to {TAIL ~ the input} winding and for causing the closed tertiary winding to load the transformer so that little, if any, a.c voltage is induced into the secondary winding in the absence of d.c. control voltage on the input winding 
A source of a.c . voltage is coupled through the output winding to the primary winding for inducing a.c . voltage signals in the secondary winding when { HEAD ~ d.c . control voltage } is applied to { TAIL ~ the input } winding and for causing the closed tertiary winding to load the transformer so that little , if any , a.c voltage is induced into the secondary winding in the absence of d.c . control voltage on the input winding
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH