Self-bias phase inverter or cathode follower

Circuit #2

A self-biased stage you compute in 3 ways:

  • either as self-bias phase inverter (Ra ~ Rk)
  • or as a cathode follower (Ra = 0)
  • and if you null Rk, you end up with the normal basic amplifier stage

Additionally, you may use it as a high impedance input stage for piezo pickups, by connecting the grid leak resistor to the mid-point of the cathode resistors, while decoupling Rgk. This bootstrap effect multiplies the apparent grid leak resistor as the voltage on the mid-point tends to mirror the input voltage. More details in “Designing Valve Preamps for Guitar and Bass” of Merlin Blencowe, page 89.


Select T1 type
V supply
Ω anode output resistor
Ω bias resistor
Ω cathode output resistor