Electro Mechanical Variable Resistor (EMVR)

The operation of a transistor functions as a valve for a larger direct or alternative current. The valve handle is turned by a smaller current from a low current source, hence the use of a transistor as an amplifier or a switch.

Is it possible to use an electromechanical device in place of a transistor? One option is to use a relay, which uses a small current to switch an larger current. An electromagnetically operated switch as a relay has been in use since the days of the telegraph.

Other alternatives to the transistor include the vacuum tube, which is an electronic device, the transformer amplifier, which is a electromagnetic device. The vacuum tube was superseded by the transistor and is complex to build, requiring high voltages.

The NEMT seems to be a little related to this area:

The introduction of vibration-based Nano Electro-Mechanical Transistors (NEMT) opens a new horizon for mechanics in computer science. NEMT working principle is based on an electrical charge shuttle between two electrodes operated by a vibrating conductor body.

https://www.sciencedirect.com/science/article/abs/pii/S0888327013000927

A mechanical nano transistor could be used in high temperature applications such as rocke engines:

https://phys.org/news/2010-09-mechanical-logic-gate-levers-transistors.html

There is the amplifier using a capacitor and an OP-amp.

http://class.ece.iastate.edu/ee508/labs/EE%20508%20Lab%204%20Fall%202012.pdf

A capacitor based amplifier could be constructed using the oscillator circuit and superimposing the signal on the carrier wave form. The entire waveform could be used to drive an osciallation in a more high current circuit, resulting in amplifitication. The carried wave then could be removed from the signal using another circuit.

https://www.instructables.com/Variable-Frequency-Oscillator-Using-Relay-and-Capa/