Abstract: A family of wideband amplifier circuits using series and shunt feedback over two stages to achieve constant impedance, including single-ended, single-ended input/differential output and differential input/differential output forms.

Abstract: A non-return valve for supply cocks, comprising an integral cup-shaped valve body (8) accommodating a substantially rigid washer (14) forming a seal with respect to the supply cock (2) and having flow apertures (16), as well as a flexible membrane (15) located underneath and self-positioning, during closure, against the said substantially rigid washer (14) so as to close the said flow apertures (16) of the same (14) and move away from the said flow apertures (16) under the pressure of the water supplied. The substantially rigid washer (14) and the flexible membrane (15) may advantageously be joined together so as to form a composite washer (28). The valve (1) proposed has a small number of components and can be very easily assembled. The substantially rigid washer (14), or the composite washer (28), has an external thread (14a)so that the said washer (14; 28) can be screwed into the thread (8b) of the cup-shaped portion (8a) of the valve body (8).