Abstract: The power (performance) of an electric arc welder is controlled in dependence upon the changes in the level of the pool of weldment with respect to the level of the adjoining surfaces of the workpiece. The level of the pool of weldment is detected by measuring the arc voltage and, in accordance with the invention, the distance between the end of the fusible electrode and the level of the workpiece upper surfaces adjoining the pool is maintained constant.

Abstract: Air is pumped from an upper chamber in a cylindrical housing through parallel groups of Ni-Cr steel heating tubes to a lower chamber communicating with a carbon-dioxide adsorber in an air-rectification system. The tube groups are suspended at their upper ends from respective Al.sub.2 O.sub.3 -ceramic holder plates seated on flanges projecting into respective openings of a carrier plate in turn removably fastened to the inside of the housing. The tubes in each group are connected in series with one another to a voltage source, the lower ends of the tubes in a group being gripped by a form-fitted ceramic spacer slidably inserted into a pipe section aligned in a support plate with an associated opening in the upper carrier plate, thereby ensuring the electrical insulation of the tubes. The holder plates and the openings are shaped as circles or as circular sections.