The base of {HEAD ~ electrodes} of transistors Q1 and {TAIL ~ Q2} are fed a controller 14 via lines 15, 13, respectively as shown 
The base of { HEAD ~ electrodes } of transistors Q1 and { TAIL ~ Q2 } are fed a controller 14 via lines 15 , 13 , respectively as shown
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH