are in turn coupled to the primary of the transformer 12 the system 20 can be installed on new tig welding equipment and can be retrofitted onto existing tig welding equipment the function of the resistor diode networks 54 and 56 is to insure that the transistor 32 is completely turned off before the transistor 34 is turned on fig5 illustrates the effects of the networks 54 and 56 as can be seen output on the line 28 is slightly out of phase with output on the line 30 the respective transitions are shifted approximately 20 microseconds with respect to one another this insures that both transistors are turned off before an attempt is made to turn either one of them on while the circuitry of fig4 above is effective to generate the high frequency arc stabilizing signals usable to start a dc tig arc and required for the continued maintenance of the ac tig arc the continuously present high frequency high voltage output signals from the spark gap oscillator 14 can disrupt the welding system control circuitry in welders which utilize silicon controlled rectifiers to switch the output current a timing network is very often used which is triggered by a zero crossing detector the zero crossing detector detects when.