A train of positive going pulses is fed to the base electrode of {HEAD ~ transistor Q1} by {TAIL ~ controller} 14 via line 15 
by
A train of positive going pulses is fed to the base electrode of { HEAD ~ transistor Q1 } by { TAIL ~ controller } 14 via line 15
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH