Primary Importance of Impedance

Radio Record, Volume II, Issue 7, 31 August 1928, Page 28

Primary Importance of Impedance

There can be no doubt, in the mind of a technical reader, that the fundamental constant of a valve, which indicates its suitability for any particular purpose, is its imnedance, since this must in all cases be suited to the propecties of the components in the anode circuit of the salve. Provided that a valve has an impedance suitable for the conditions under which it has to ‘work, it may be regarded as correctly chosen from among the many types available. | It follows, therefore, that a statement of the impedance of the valve should hold the most prominent place of all in the abbreviated description. The next most important constant is 1: amplification factor, which serves to indicate which individual valve, among a number whose impedance is the same, will in practical use give the greatest. amplification. The figure representing the amplification ‘factor should therefore. be given a place in the abbreviated description of the valve, but this place should be secondary to that held by the impedance. Thirdly, the user, who will be in possession of either a 2, 4, or 6-volt accumulator, requires to know’ the filament voltage necessary to operate the valve, and this information also should be given; but, since the filament voltage has no great bearing upon the performance of the valve, it should not be given any prominent place in the description. The filament current in these days of economical valves is of least importance except when dry batteries are used for the A supply.