The Tektronix P6139 is a passive miniature 500 MHz ×10 scope probe for 1 MΩ // 8-18 pF scope inputs.
It has a ×10 readout pin, and shares accessories with many other Tektronix subminiature modular probes.
|Input impedance||10 MΩ // 8 pF|
|Intended for||TDS500 series, TDS3054|
Unless they've had their cables replaced, they had a whisker- or dendrite-growth problem in the cable that will short out the signal and drive you nuts. It can be cleared by running some current through the BNC connector but only temporarily. The only fix is to order a new cable from Tektronix, which I'm not sure you can still do.