Question 4.7: In the triode amplifier of Fig. 4-14, VGG = 4 V, VPP = 300 V......
In the triode amplifier of Fig. 4-14, V_{GG} = 4 \text{V}, V_{PP} = 300 \text{V}, R_L = 10 kΩ, and R_G = 2 kΩ. The plate characteristics for the triode are given by Fig. 4-13(b). (a) Draw the dc load line; then determine the quiescent values (b) I_{GQ}, (c) V_{GQ}, (d) I_{PQ}, and (e) V_{PQ}.
(a) For the given values, the dc load line (4.11) has the i_P intercept
i_P = \frac{V_{PP}}{R_L} – \frac{v_P}{R_L} (4.11)
\frac{V_{PP}}{R_L} = \frac{300}{10 × 10^3} = 30 \text{mA}
and the v_P intercept V_{PP} = 300 \text{V}. These intercepts have been utilized to draw the dc load line on the plate characteristics of Fig. 4-13(b).
(b) Since the polarity of V_{GG} is such that v_G is negative, negligible grid current will flow (I_{GQ} ≈ 0).
(c) For negligible grid current, (4.10) evaluated at the Q point yields V_{GQ} = -V_{GG} = -4 \text{V}.
I_{G} = -\frac{V_{GG}}{R_G} – \frac{v_G}{R_G} (4.10)
(d) The quiescent plate current is read as the projection of Q_n onto the i_P axis of Fig. 4-13(b) and is I_{PQ} = 8 \text{mA}.
(e) Projection of Q_n onto the v_P axis of Fig. 4-13(b) gives V_{PQ} = 220 \text{V}.