Mains valves and power supplies
Chas E. Miller
As mentioned in Chapter 6, valves for mains operation have an indirectly heated cathode as the emissive electrode. Apart from this they operate in the same way as battery valves and may be substituted for them in all the applications we have looked at in the previous two chapters. In fact, the two TRF circuits shown and described could very easily be converted to mains operation with the addition of a power supply unit and a few other components. The great difference is that since power from the mains is cheap and virtually unlimited the valves can be made to perform much more effectively; in particular very large power outputs may be obtained.
Cathode bias
Mains valves need negative grid bias ...
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