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Valve Theory Continued.

Indirectly Heated Cathodes.

The foregoing text has assumed that the necessary heat to ensure electron emission results from passing a current through the cathode, however this is not usually the case in practice. More often a separate heating element is provided. This heating element is a wire located in very close proximity to - but electrically insulated from the cathode. Current passing through the heater wire causes an increase in temperature thereby heating the cathode indirectly.

Valve Characteristics.

It is beyond the scope of these short paragraphs to discuss valve characteristics in depth, however there are perhaps three that are deserve a one line explanation. The valve impedance refers to the anodes resistance to alternating current (AC). Its value is calculated by altering the anode voltage by a small amount , then dividing this by the change in anode current flow.

This and the foregoing pages of valve theory are still under development, diagrams and further information to follow.

Continue to see all the components of a Pentode valve on the next page

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