NEW RADIO VALVE

Otago Daily Times, Issue 21983, 19 June 1933, Page 14

NEW RADIO VALVE

ALMOST UNBREAKABLE. * (Fbom Oub Own Cobbespondent.) ': May ; 12. . Some publicity is being given to a new radio valve which is .said to be almost unbreakable and to possess a number-of other desirable .features. ~"/., - . ... • ; The Marconi,Catkin is, the "outcome, of considerable ; research and experiment, directed v towards i.the -. improvement of standard valve construction. ~. ... The first object was to achieve an absolutely rigid and interlocked electrode construction with a more - stable .basis of support than the conventional pinch;, secondly, it was. considered desirable to promote cooler .'running- of 'the'grid and anode, particularly in mains valves where the energy to be dissipated is considerable; thirdly, an' improvement 'in uniformity should be achieved; fourthly, an inherently flexible mounting would reduce microphonics; fifthly, a reduction in bize would be welcome. ■-" On inspection the first innovation which meets the eye is the absence of the familiar glass bulb.. Existing methods of manufacture are based on lamp technique and involve the use a glas. bulb because of its transparency to light. In a valve a transparent container is not essential, so Marconi " Catkin " uses, its anode as the envelope for containing ,the vacuum, hence at one stroke disposing of the (most vulnerable element of conventional design. ' • The anode is cylindrical, possessing sufficient' inherent . strength to withstand atmospheric pressure, as well ae forming a perfectly, rigid'and highly accurate, support for the electrode system contained within. '., ~ , ' - ' A LOWER TEMPERATURE: By.promoting the more efficient radiar tion of heat the whole electrode system operates at a lower temperature than in a glass vaive, and any tendency for occluded gases or . water vapour to be set free in the'vacuum ■ is greatly lessened. The anode temperature of a "Catkin" output valve is so far below that of its glass counterpart that the intense eddy current and bombardment heating processes'during pumping are eliminated. The Cathode, heater and grid; or grids are built up as a unit in an entirely new manner. In the normal valve the electrode supports are held by a glass "Pinch" which forms the foundation of the whole electrode system. This pinch, j although in most respects quite satisfactory, is liable to distortion and inaccu- ( racy, as well as introducing a number of ' welds and bends into the supporting wires. The Marconi "Catkin"' pinch consists of a pressed steel clip with mica insulation, which cannot distort or shift. It is proportioned in such a' manner as to eliminate all bends in the electrode supports, and so. contributes again to greater accuracy' and strength. Welds also are almost '■ eliminated. This' electrode assembly carries stiff mica spacing washers fitting closely into the anode and ensuring meticulous alignment. ■ The limits of variation from valve to valve are in consequence greatly reduced; while noise and microphonic troubles are very markedly lessened. Finally, the circular glass seal is completed and the connecting wires brought out round the resultant annular nm. Here again, these leads are well spaced in comparison with the somewhat restricted width of a standard glass pinch, and leakage is therefore minimised. The completed valve is now mounted on a rubber ring firmly held in a metal cap, and fitted with a thin moulded disc carrying the usual five pins. Here is another step forward in the reduction of microphonics and noise in operation, as the electrodes are. effectively insulated' from mechanical vibration of the chassis. In the case of valves to be employed in place of the existing " unmetallised" types, the anode is sprayed with'a heatresisting insulating enamel, but where the equivalent of a "metallised" valve is required the Marconi " Catkin " is fitted with an attractive perforated outer metal shield, connected to the cathode pin. This valve may be dropped on to a hard surface without damage, and is practically unbreakable. Even when so covered the " Catkin" possesses one final advantage which modern receiver design renders of primary importance. With a maximum overall length of 125 mm. and diameter of 33 mm. it is considerably smaller than the glass equivalents, especially in the power and pentode types. The first issue of Marconi " Catkins" will comprise four types— VMS 4, MS4B, MH4, MPT 4. SOME ADVANTAGES. The following advantages are claimed for this type of valve:— 1. Almost unbreakable, owing to metal construction and interlocked electrodes. 2. Great uniformity, due to extreme accuracy of electrode alignment, steel and mica pinch, straight support wires, few welds. 3. Increased reliability, as anode in direct contact with air promotes cooler running, thus less chance of gases or water vapour being set free. 4. Less microphonic owing to rigidity and rubber mounting. 5. Solid metal shield gives better screening than metallising on glass bulb. 6. Smaller size, hence more compact sets, great saving in storage space. 7. Base cannot work loose or come off. 8. Easy transit. Carton one-quarter to one-sixth size of present: types, can be sent by post with no special packing.