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Example of Solids and semiconductor devices

Example: a type 6J5 triode has a transconductance of 2600 µ  mho and a plate resistance of 7700 ohm when operated with a plate supply voltage of 250 volt and a grid bias of- 8 volt . Find (a) the maximum possible gain of the amplifier, employing this tube, and (b) the actual gain when used with a plate resistance of 50,000 ohms.

Solution:

Here, g _m =2600 × 10^-6 mho; r_p = 7700 ohm

As    µ = r_p× g _m = 7700 × 2600×10^-6=20.03=20

(a)    The maximum possible gain corresponds to µ to the tube. As such its value is 20.

(b)   R_L = 50000 ohms; Voltage gain, A_v=µR_L/(R_L + r_p)

=(20 ×50000)/(50000+7700)=17.3