Abstract: 1. In a proximity fuze comprising a target-responsive circuit including a first electronic grid controlled tube and a squib detonating circuit including a second electronic grid controlled tube; a B tube voltage supply for said tube circuits comprising a condenser, an external connection for charging said condenser from an external source, and circuit means for connecting said condenser to said tube circuits, said circuit means including a biasing resistor connected between the minus terminal of said condenser and the cathode of said first grid controlled tube, a second biasing resistor connected between the grid of the second grid controlled tube and the minus terminal of said condenser whereby when the B drain of the said fuze exceeds a predetermined level, the bias on said second grid controlled tube is reduced to the firing point, thereby igniting said squib.