The X150 is the M-OV Type designation for the Philips/Mullard ECH42. It is a triode hexode mixer in an all glass envelope fitted with a B8A base and designed for radio receivers.
The metal skirt has the locating pip required as the eight pins are equi-spaced around the base. The lettering is Made in Holland. Philips not M-OV manufacture in Holland and so this was made for M-OV by Philips.
Looking through the screen a small structure can be seen near the top - this is the triode oscillator that feeds the hexode mixer below.
The thin glass tube envelope is 20 mm in diameter, and excluding the B8A base pins is 54 mm tall.
References: Data-sheet & 1040. Type X150 was first introduced in 1948. See also1948 adverts.