Abstract: Compact, low power fluxgate magnetic sensor readout circuits and apparatus are presented in which demodulator or rectifier circuit to modulates a sense signal from the fluxgate sense coil, and the demodulated signal is provided to an amplifier circuit with a transconductance or other amplifier and one or more feedback capacitors connected between the amplifier input and amplifier output to integrate the amplifier output current and provide a voltage output signal indicating the magnetic field sensed by the fluxgate sensor.

Abstract: Tube amplifier system including a plurality of conductor walls extending parallel to a longitudinal axis and defining an interior space therebetween. The tube amplifier system also including a shorting deck that extends transverse to the longitudinal axis. The shorting deck is electrically coupled to the conductor walls. The tube amplifier system also includes a movable tray assembly having a grounding deck that extends parallel to the shorting deck. The grounding deck and the shorting deck define an output cavity therebetween that has a length. The movable tray assembly is removably mounted to at least one of the conductor walls such that the grounding deck is capable of being positioned at multiple different levels along the longitudinal axis to change the length of the output cavity.