1,195,247. Protective arrangements. LICENTIA PATENT-VERWALTUNGS-G.m.b.H. 13 Sept., 1967 [13 Sept., 1966], No. 41725/67. Heading H3W. [Also in Division H2] A transmitter valve 8 is protected under excess current conditions, e.g. due to a flashover, by an ignitron 5 and a resistor 4 connected across the smoothing capacitor 3 of a rectified A.C. supply, the ignitron 5 being triggered by a thyristor 61 which is rendered conductive when the current sensed by a transductor 9 exceeds a value determined by a threshold device 10, e.g. a Zener diode. An amplifier 11 may be provided. A second ignitron may be connected with reversed polarity across the ignitron 5 and a further ignitron with a series resistor may be connected directly across the valve, Fig. 2 (not shown).