Abstract: The invention relates to a flash TV evaporator for the evaporation coating of cathode ray tubes with aluminium, having a cavity from which the aluminium is evaporated when a current flows through the flash TV evaporator, wherein the width of the cavity tapers from the upper edge of the evaporator to the lower edge of the evaporator.

Abstract: The apparatus for detecting gases comprises a photoacoustic gas detector 35, in which the intensity-modulated absorbed test light beam 32' is converted into noise and detected by means of microphone 36. The photoacoustic gas detector 35 is acoustically decoupled from the gas collecting point 54 by a gas-permeable diaphragm 52 or a rigid, porous material 52'. The gas chamber 35' of photoacoustic detector 35 can be scavenged by means of supply lines 38, 38' and valves 56, 56'. It is advantageous to use a thermal source 32 intensity-modulated by phase lag. The signal is processed at microphone 36 by means of a N-path filter comprising cyclic switch 63 and R-elements 62, 65, 65'. The apparatus can be used for detecting CO.sub.2 and CO.