Long time ago I developed a CCS board which provides full flexibility in terms of FETs/MOSFETs used. It was a 2-terminal CCS, a very well known circuit.
Recently, I looked at developing a small PCB to hold a basic CCS with depletion FETs. The top device is for the IXTP08N100D or DN2540 in a TO-220 case which can be bolted or use a clip-on heatsink. The lower device is a SOT-23 SMD FET. I use from BF862 to J105 /112or J113. Current ranges from 1mA to about 40-50mA depending on the sample IDSS you get on the FET. There are a few combinations quite interesting for very low Tempco. In the ETF.18 lecture I published on the blog, there are a few points and formulae to get the best tempco configuration with these FETs.
This CCS isn’t the most stable one from a tempco point of view. There are other and more complex circuits to look into if you need so. Generally speaking, these CCS are more than stable enough for the valve audio circuits we work with. And that is more than good for me.
Having a small footprint of 3 x 4 cm on the board is pretty good.