Rcceivcd I9 August, I9iOJ List of symbols used I, = tinrc of half-cycle with tmnsistor TR I ' off ': = ' space ' time period I, = time of half-cycle with trausistor TR.7 ' off ', = ' mark ' time period. t,/1, = mark-space ratio. h,,,(,, ; u~d h,E(,l=large-sigual current gain of trnusistors I and T R l , respectively. I7,=d.c. collector supply voltage. V,Ec,,t,= transistor collector-to-enritter voltage wlreri fully ' on '. 17,,,,,,,,,= t r a~~s i s t o r base-to-emitter voltage when ' on '.I,, and I,,=d.c. collector currents of transistors T R I and 11:R,2. respectively. I,,, and 11,2=d.c. base cnrrents of tmnsistors T R I and T l t l , respectirely.