Cathode follower
The cathode follower (also Katodenfolger , anode base circuit ) is a tube basic circuit . It is mainly used as an impedance converter because, in contrast to the cathode base circuit, it has a low output resistance. Its gain is always <1.
The input signal is fed in between E and ground , while the operating voltage is applied between the U (connected to the anode ) and ground. The capacitors C1 and C2 ensure a DC voltage-side decoupling between the circuit and upstream and downstream further parts. The output signal can be picked up between A and ground.
The resistors R1 and R2 are used to determine the operating point by automatically generating the grid bias on R2. R2 and R3 form the working resistance of the tube. The output resistance of the circuit is determined by this working resistance and the steepness of the tube at the working point.
The signal fed in at the input generates a (largely) in -phase current through the tube, as well as R2 and R3. This change in current results in a (largely) in-phase voltage across the series circuit of R2 and R3. The resulting voltage raises the cathode potential in phase with the control grid with respect to ground, which ultimately results in a lower control voltage of the tube and thus reduces the gain: The voltage between control grid and cathode is relevant for controlling the tube, not between control grid and ground. This negative feedback reduces the gain of the circuit to <1.
The picture shows the circuit using a triode , but is also often used with tetrodes and pentodes .
literature
- Otto Diciol: Tube -NF-amplifier internship . Franzis' Verlag, Poing 2003, ISBN 3-7723-5587-0 (reprint).
- Winfried Knobloch: Tube technology is very modern . Pflaum Verlag, Munich 1993, ISBN 3-7905-0660-5 .
