This classic Tektronix current probe uses transformer action to measure AC current flowing in a wire. Insertion impedance is quite low, 2.8 uH parallelled with 4 mR, in series with 1.7 nH. Deflection factors are typically 1 mA/div to 1 A/div. It has no internal frequency compensation. The datasheet shows 1 primary turn and 125 secondary turns.
It can be used with a passive termination or an amplifier unit, such as a type 134 or 7A14, a.o. With a type 134, bandwidth extends from 12 Hz to 40 MHz.
Ferrite core transformer. Note the arrow that indicates the direction of current flow: current flowing through the probe head in the indicated direction gives rise to a positive deflection.
Top and bottom of transformer and insides of probe. The probe is clamped around the wire and closed to complete the magnetic circuit in the transformer.
P6019 connected to 7A14 current probe amplifier in a 7623A analog storage mainframe measuring its own supply current. The 7623A is configured in variable persistence mode to capture the slow 50 Hz signal. Peak-to-peak current is 7.5 A! The 7623A supply is a linear one.