I´m studing to build a simple tube preamp like this one in the schematics. I´m doing some software simulation and the preamp works. It increases the signal. BUT I would like to be able to control the amount of increasing gain. How can I add a pot to control the gain?
I did change the first 1M resistor to a 100k potentiometer , wiring the variable pot pin to the tube´s grid (pin 2). And it seems to work all right in the measureaments. But i´m not sure if I don´t this right. Thanks!