Tektronix current probe amplifier tcp300 and tcp400 series and probes tektronix tcpa400 the tektronix tcpa400 is a dc to 50mhz current probe amplifier a highly advanced current measurement system for todays current measurement needs for even higher current levels the tcpa400 amplifier when used with the tcp404xl current probe measures 500a dc continuous and 750a dc continuous derated with duty cycle tektronix tcpa400 current amplifier 50 mhz