The Modern Valve

Radio Record, Volume II, Issue 24, 28 December 1928, Page 32

The Modern Valve

4 ' Story of ‘Its E volution. . ‘ ® rT'HE story of the modern valve.is ‘as interesting and enlightening as any page of radio history. It shows how man, continually striving’ against odds, has finally evolved a piece of apparatus that has made reception as we understand it possible. Radio reception was first made possible by the discovery of the crystal as a detector. Round this, a set was built, and for long years radio history was practically at a standstill as far as | receivers were concerned. Sounds could be received from short distances, but could not be amplified. | Then: came the vacuum tube,. or valve, consisting of a wire capable of emitting electrons when heated, a sheet of metal to receive them, and a fine wire mesh to regulate the flow. These had special properties when enclosed in a vacuum tube-that of amplifying the incoming signals. NCE having the che, radio development went on apace, When broadeasting first became popular, in 1921, the valve in general use was the 0.1 type, used for all purposes in the sets of that day. This valve required one ampere of filament current at five volts, and had a high internal resistance. If a set had seven or eight valves, an ‘enormous load was placed on the battery, and even 4 two-valye set drew:as much current as a modern eight-valve set. — In the spring of 1922, this was superseded by the .01A valve, having -ampere filament at five volts, a plate impedance of 10,000 ohms, a mutual inductance of 800 microhms at 90 volts plate. Grid voltage had not yet been applied. Pte

‘By cutting the filament to one-fourth a great incentive to multivalve sets was created, and thereafter the future of radio as a household instrument, was assurred. MPROVEMENTS were made steadily till 1924, when the elements were made more rugged, and the grid and plate structures were moved closer to‘gether, thereby increasing the mutual conductance to 1000, and reducing the impedance. Minor improvements have still beén effected, but none of revolutionising importance, except, perhaps. two, which are a modification of the ordinary ‘vaive. . The alternating current valve, which would operate. from the electric mains with the addition of a small transformer promised to effect great changes in the sets oto.

~~ where power was available. They did not, however, accomplish what was expected of them, it being found that the smooth current in the ordinary valves produced generally the better results. [THE screened grid is, however, the most promising of modern valve modifications. This valve showed itself capable of great accomplishment when in the hands of someone who Was capable of using it to its best advantage. The earlier type had double ends and would not fit the normal base, but this has been rectified, and the modern screened grid fitting a standard socket has an extra terminal at the top. . It has been found that this valve gives greatest service on the high frequeney side of the receiver. NV ENTION has not been made of the double and triple grid valves. The former’ is of special value to those wishing high amplification for low plate voltage and filament consumption. Although usually of high resistance, this valve is of great value to the crystal owner who desires to amplify at low cost. — The penthode (triple grid) is capable of great achievement as a final power valve. It requires high voltage, but with an amplification of 100, it is to be preferred when eliminators are available. Valves have been united to form two-in-one and three-in-one valves. In these eases.the parts of three valves are enclosed within a single vacuum tube. : Each adaptation has its particular advantage, and radio has become s0 specialised that a valve in its wrong place causes distortion and may spoil an otherwise perfectly good set.