VALVES IN PARALLEL

Shannon News, 30 March 1928, Page 4

VALVES IN PARALLEL

It is often recommended that in the putput stage of a receiver if one jpower valve will not handle the power, two valves in parallel should fie used. This is useful where a valve pf the ordinary small power class is first being overloaded, but is is not desired to incur the heavier filament current of the large power class. Two yalves similar to the one already W use may be used in parallel. It is desirable, though not essential, that the valves connected in parallel should be pf the same type. At any rate the characteristics should be the, same. The circuit is simple, the two grids are connected tajjether and similarly with the two plates. Probably few realise what are the constants of two similar valves connected, in parallel. In the first place the voltage amplification factor is not changed, but is equal to that of one of the valves. <pn the other hand, the A.G. resistance is halved. For a given high tension voltage and grid bias the plate current is doubled, while the filament current is also doubled. With two matched valves and a load equal to their combined A.G. resistance, twice as much power can be handled as by one of the valves having a load equal to its A.C. resistance. 'Thus it is seen that tlm use of two or more valves ip parallel will enable a heavier power to be dealt with than is possible with i a single valve. Where it is desired to operate loud speakers at more than usual volume the paralleling of output v,alves should be tried.