{TAIL ~ Voltage converter} with GTO thyristors in series connection with {HEAD ~ at least a choke} with freewheeling circuit 
{ TAIL ~ Voltage converter } with GTO thyristors in series connection with { HEAD ~ at least a choke } with freewheeling circuit
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH