Hi,
this is my DIY current clamp calibration rig. It consists of a bi-directional current source built from a CRT vertical deflection IC (TDA4866) and a DIY 50-Turn Current Coil (Fluke 5500A clone).
I choose the TDA4866 because I had a few lying around and its designed to drive a current through a coil. Being a full bridge chip means I just need a single supply (15V DC in my case).
It can push 1 Amp RMS through my 50 turn coil up to a few KHz just fine.
Here's the schematic and some pictures.
PS: Big thanks to my lovely wife who wound the coil.