Abstract: Two sources of alternating current, such as taps of a supply transformer, e selectively switchable across a load by means of two circuit branches each provided with a main switch and a collateral network in parallel therewith, this network comprising a series combination of a protective resistor, an ancillary switch and a pair of antiparallel thyristors. The gates of the thyristors of each pair are interconnected by a firing resistor in series with a disconnect switch; each gate, furthermore, is connected to its own cathode through a reverse-poled diode which enables the ignition of the opposite thyristor upon closure of the disconnect switch when the proper polarity of the source voltage appears across the network in the closed state of the associated ancillary switch.

Abstract: A load-switching circuit for a tapped transformer utilizes identical netws of antiparallel thyristors bridged by commutating networks having a condenser in series with a damping impedance. According to the invention, the blocking of one pair of thyristors causes the energization of a relay to operate a switch contact shunting the damping impedance of the blocking pair so that its condenser functions as a voltage spike surge suppressor.

Abstract: The grinding and polishing machine has a tool-carrying spindle (1) driven th a combined rotating and rocking action. It has a driving shaft (4) which is reciprocated axially and passes through a disc (8) which slopes at an acute angle. Above this disc is a second disc attached to the shaft, with a roller (5) attached to its periphery which rotates against the sloping disc. The tool spindle also passes through another sloping disc and through a plate (12) with a peripheral roller (16) which travels against this second sloping disc.The tool spindle carries an arm (13) with a dog projecting from it to fit into a hole in the plate to rotate the same. This plate also has a dog (14) which fits into a hole (15) in the disc attached to the driving shaft so that it transmits rotary movement for driving the tool spindle.