Apparatus for accelerating cathode heating

Claim 1

Apparatus for accelerating the heating of the cathode heater of a cathode ray tube or the like comprising: a first self-heating positive temperature coefficient resistor having a relatively low initial resistance which increases abruptly as its temperature rises above a given level; means for interconnecting said resistor to an electrical power source thereby rapidly to heat it above said given level; a second self-heating positive temperature coefficient resistor positioned in heat-exchange relationship with said first resistor and having a relatively low initial resistance which increases abruptly as its temperature rises above a given level; a resistor of substantially fixed resistance shuntconnected with said second self-heating resistor; and means for interconnecting said shunt-connected resistors in series with the heater of said cathode across an electrical power source adapted to supply power of a substantially constant potential in excess of that required to maintain the heater of said cathode at a predetermined temperature; the resistance of the second self-heating resistor being not substantially more than that of the fixed resistor at temperatures below its aforesaid given level But substantially greater than that of the fixed resistor at temperatures above its aforesaid given level, whereby after power is initially supplied to the cathode heater its potential will be reduced from a level substantially in excess of that required to maintain the heater at said predetermined temperature to a level which maintains the heater at substantially said predetermined temperature as the first and second resistors self-heat thereby to increase and then maintain said second resistor at a temperature above its aforesaid given level.