Figure 4 eh.9. Small signal model of a triode with its cathode resistor unbypassed. There are two terminals on the left, the top one is labeled G for grid. The bottom one is not labeled. The two are labeled collectively V in. The top one G is marked with a plus sign and the bottom one with a minus sign. The bottom terminal goes to ground. Between the two terminals and set to the right a little is a reference point labeled K. There is a minus sign next to this point. There is an AC voltage generator labeled minus mu V gk. The bottom end of this generator connects to the point labeled K. The lower end is marked with a minus sign. The upper end of the generator is marked with a plus sign and goes to the left end of a resistor labeled r p. The r is lower case. The right end of the resistor connects to a terminal labeled P. The resistor is marked with polarity with plus on the left and minus on the right. Directly below the P terminal is another one labeled K. It connects back to point K and the bottom of the generator. A resistor labeled R k connects from the K terminal to ground. An arrow indicates that a current I b is flowing upward in R k. R k is also marked with polarity with the top being negative and the bottom being positive. The P terminal connects through a resistor labeled R b c to ground. An arrow indicates that I b is flowing downward through R b c. Polarity markings indicate that the voltage across R b c is positive at the top and negative at the bottom. End verbal description.