Maser
Active filters.
Amplifying magnetic fields can enhance the performance of a device or system by increasing the strength of the magnetic field, which can improve efficiency, sensitivity, and overall functionality. This can lead to better performance in applications such as data storage, medical imaging, and power generation.
A Geiger Counter
A Geiger Counter
A RF amplifier is a device for electrically amplifying the power of an electrical signal, typically, but not exclusively, radio frequency signals.
I would say an ethernet extender/booster/repeater.
A magnetron is a device commonly used for generating microwaves in microwave ovens. It works by utilizing the interaction of electrons with a magnetic field to produce electromagnetic waves at microwave frequencies.
If by triode, you mean "a three-electrode tube", then yes. You need a source of current into the device, a control electrode, and an "outlet" for the controlled current. Although there were radically different types of construction, all early amplifying tubes were triodes of some kind.
A Geiger meter satisfies those requirements.
A repeater. Repeaters work only on layer 1 (Physical) of the OSI model.
Roughly speaking, resistance. Transconductance refers to the reciprocal of the amplifying device's internal resistance. The concept is particularly useful if the device is a voltage-controlled current source (tube or FET). In vacuum tube amplifiers, transconductance (Gm) is (u / Rp), where... u is the amplification factor. u= (Gm x Rp). Rp is the anode (drain) resistance. Rp is the internal resistance of the amplifying device. Gfs is synonymous with Gm. The reciprocal of Gm (or Gfs) is (Rp / u). Another term for this reciprocal is transresistance.