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of a triode to the input. This effect is a prime-limiting factor in applying triodes. It is a major reason why
triodes are seldom used—especially at the higher frequencies.
MU AND TRANSCONDUCTANCE are measures of tube efficiency. Mu (µ), or amplification
factor, is a measure of the amount that plate voltage varies in relation to variation of the input voltage.
Mathematically, mu (µ) is expressed as
TRANSCONDUCTANCE, on the other hand, is a measure of the amount of variation of plate
current caused by a variation of the input signal. Mathematically, it is expressed as:
TETRODES were developed to compensate for the effects of interelectrode capacitance. Placing a
positively charged screen grid between the control grid and plate has the effect of adding a capacitor in
series with the capacitance that exists between the control grid and plate. This reduces total capacitance
below the value of either capacitor as shown by applying the formula:
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