The heater 56 has both ends connected to a heater power supply 58 which controls {HEAD ~ the heating temperature} of the heater 56 to regulate {TAIL ~ the temperature} of the cathode 14, so that an amount of electron emission is controlled to adjust the tube current 
to regulate
The heater 56 has both ends connected to a heater power supply 58 which controls { HEAD ~ the heating temperature } of the heater 56 to regulate { TAIL ~ the temperature } of the cathode 14 , so that an amount of electron emission is controlled to adjust the tube current
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH 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