Question

Find the values of r_p, µ and g_m of a triode operating at plate voltage 200 V and grid voltage −6. The plate characteristics are shown in the figure.

Answer 1

Dynamic plate resistance, `r_p=((deltaV_p)/(deltaI_p)),` at constant grid voltage

We need to find the slope of the graph for a particular value of grid voltage, i.e. V_g = −6 V.

Consider two points for the plot of V_g = −6 V:-

\[r_p    =   \frac{(240 - 160)  V}{(13 - 3) \times {10}^{- 3} A}\]

\[ r_p  =   \frac{80}{10} \times  {10}^3 \Omega\]

\[ r_p  = 8  K\Omega\]

\[ g_m  =    \left( \frac{\delta I_p}{\delta V_g} \right)_{V_P = \text{constant } (200  V)}\]

Consider two points on the 200 V line:-

\[g_m    =   \frac{(13 - 3) \times {10}^{- 3}}{[( - 4) - ( - 8)]}A\]

\[ g_m  =   \frac{10 \times {10}^{- 3}}{4}=2.5\text{ mili mho}\]

Amplification factor,

\[\mu   =    -  \left( \frac{∆ V_P}{∆ V_G} \right)_{i_P =\text{ constant}}\]

\[\mu =  - \frac{100 - 180}{- 6 - ( - 10)}\]

\[\mu = \frac{80}{4} = 20\]