Today I finished CCS module on PCB, LED+BC558B/MJE350 version, from the book "Valve Amplifiers - third edition" by Morgan Jones. I can`t post the schematic, it`s on the page 138. Two transistor cascode, 120 Ohms resistor is set for 8mA, for larger current this R must be lower.
Well, I use marker + my favorite nail-polish (hehe), and results are not that spectacular, but "good enough". Then Fe-III-Chlorid does the rest. I fixed the heat sink with 2 mm screw from the Cu-side (tricky, sink is only 4 mm thick). Small dimensions of the board (33x75 mm) need precision... I added C1=1uF/630V MKT cap for local decoupling.
One of these days, I`ll try it (2A3 driver load, etc.).
And one more thing - I did my best to build it and describe it, but can`t guarantee the success...doesn`t mean to discourage anybody, but lot of patient work is needed... And beware of high voltage...