RADIO NOTES

Patea Mail, Volume XLIX, 7 October 1927, Page 3

RADIO NOTES

By Audiotroa.

VALVE MANUFACTURE

Moat listeners arc aware that radio valves .contain a plate, a grid, and afilament, all contained inside a glass bulb, The three elements mentioned are known ay the electrodes and arc iirst mounted on stout nickel wires.

A piece of glass tubing accurately one end softened in a blow-pipe flame one and softened in a blow-pipe flame and spun outwards to form a funnel, or flute. The funnel is then mounteu on a jig and the nickel wires for the electrodes arc placed in position. series of iblow-pipc flames soften the opposite end of the funnel, as hich it finally squeezed round the nickel wires, thus sealing the wires into the glass. The electrode supports arc connecter ' to the socket pins by copper wircte, which are joined to them through iutei mediate pieces of line platinum wire. The use of platinum wire is es sential, since it ensures a perfectly airtight joint whore the gounccvum pass through the “pinched” portion of the. glass stem. The slightest tract of air in an exhausted bulb would render the valve “soft,” with a consequent loss of life and efficiency. (A “hard” valve' is one in which the vacuum has been carried to a very ■high degree). In making the pipeless type of valve (i.e., having an entirely smooth exterior) the air is exhausted through a. small glass tube, which it Avoided into the stem at the time the connecting wires are sealed in tlu pinch. The four composite Avircs anu the exhausting tube arc inserted in the jaws of the rotating stem-makim. machine, where they arc exposed k poAverful blow-pipe gas jets until the glass is quite soft. The molten glass is then pinched at the top end and thethe exhausting tube automatically, sealed in position. It Avill be appreciated Avith' Avhat care these operations are conducted, because unless .the glass is correctly m ; eltcd and pinched ac curately and tightly into the Avircs it would be impossible to obtain an. efficient vacuum in the later stages of manufacture. The next series of operations is concerned Avith the sealing of the electrodes to their supports, the fbament being Avoided to its supports by hand. The grid, in the form of a helix of molybdenum wire of about isix-thousandths of an inch diameter, is wound ,on a mandril of about onetenth of an inch in. diameter, cut to its .required length, and electrically Ai'elded to the backbone —a length of. nickel wire. The anode, or plate, is' made of sheet nickel of about eight thousandths of ah inch thick, and is electrically welded to its support. .With the completion of these operations the mounted stem is ready for sealing into the bulb.- As received from the glassbioAA’ing department, the bulb has Avhat might be called a useless piece of glass at the end, termed the “moil.” ‘ This is cracked off at the rim, so that a slightly flared mouth is left, into which the mounted stem is inserted. The stem is hold in a special chuck, the flared bulb placed over it, and the Avhole rotated, in a machine Avhcre the stem and bulb pass through a series of bloAv-pipc flames, the heating process being continued, until the glass of the bulb is melted into the glass of the funnel. In the process of “exhausting” the valves arc sealed, in batches of a dozen, to a glass tube, Avhich is .connected to a motor-driven oil pump. To be continued. GENERAL NOTES., With the advent or mager days Australian stations are not Avell received in the early evening. Static has not been troublesome lately and some very fine programmes have been heard. A very interesting debate on “Pro--1 hibition” was ■ broadcast from station 2PC., Sydney on Tuesday night.