Carlson SuperProbe1 MK3 with SS Probe Fully Assembled Prototype Unit Ready 2 Use
Carlson SuperProbe-1 Prototype Unit. The design is well proven and open-sourced. There are also several open-source PCB designs for the probe and amplifier, but most of them are SMD designs. Here is a great UT video of Carlson using the SuperProbe to locate a noisy component inside a complex transceiver.