24 

 VALVES 



The newcomer to the field of electronics and radio is liable to bewilderment 

 at the enormous range of valves which seem to be at his disposal; about 

 2,000 of them, in fact. He might be forgiven for feeling that to choose a 

 valve in a particular case design calculations of exceeding nicety must be 

 necessary. The author proposes to indicate how to master this embarras de 

 richesse. 

 The reasons for the profusion of types are as follows : 



(1) Plurality of valve makers. There are in Great Britain at least six 

 major manufacturers who make ranges of valves which are largely overlapping, 

 but who all have their own systems of designation. Thus manufacturers A, 

 B and C may each make a valve with identical characteristics, but each will 

 allot it a different type number. 



(2) Types of base. There are extant at the moment 16 common types of 

 valve base* and numerous more obscure ones. Partly this is explained by 

 the progressive miniaturization of valves over the years, partly by differing 

 countries of origin. Nevertheless it does not seem that the diversity is 

 altogether rationally explicable. 



(3) Number of heater ratings. Valves can be had with heaters intended 

 for parallel operation from constant voltage supplies (1-4 V d.c, 2V d.c, 

 4V a.c, 6-3 V a.c, 12-6 V a.c.) or series operation from constant current 

 supphes (0-1, 0-2, 0-3 amp a.c. or d.c). This variety is attributable to the 

 demands of the radio and television, rather than the general electronic, 

 industry. 



(4) Composite valves such as triple-diode-triodes and triode-pentodes. These 

 are produced in response to specific needs in the radio and television industries 

 and are only economic because they serve a mass market. In general electronic 

 work it is a moot point whether composite valves are very helpful (apart 

 from double triodes). They comphcate stock-keeping and mihtate against 

 flexibility in design. 



By rejecting composite valves, adhering to one heater rating (6-3 volt a.c), 

 restricting oneself as far as possible to one base (the miniature 'Noval' or 

 'B9A') and one manufacturer it is possible to produce a 'short list' of rather over 

 a dozen types. Between them they will do almost anything one is likely to 

 want, and in time one gets to know their characteristics more or less by heart. 

 The author's suggested short-list is as follows. Three kinds of base are used, 

 and three manufacturers : they are mostly MuUard valves, but only because 

 they happen to be kept by his local stockist. 



* i.e., number of pins, their sizes, separations and dispositions. 



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