(1935) Tungsram Valves, London: The Tungsram Electric Lamp Works (great Britain) Ltd.
Here we have details of Tungsram introducing the Classic or shouldered shape of valve envelope or bulb. There is no date on the booklet but looking at the valves it is probably 1935 or 1936. Reference is made to the new act of parliament setting-up the National Grid. This became law in 1926 and the grid started operating in 1933. Also some B7 based valves appear and this base dates to 1933.
The mica spreader at the apex of the envelope structure gives un-precedented rigidity whilst the unusual shape of the bulb prevents the glass ringing at any given frequency and therefore microphonity from the source (which is a very common one) is entirely obviated. The elimination of microphonic tendancies is completed by the new TUNGSRAM interlock structure and the shatterproof suspension within the bulb. The price, moreover, of the new dome shaped TUNGSRAM Valve remains the same.