I built the Mini-Mod back in June 2015 and used a BF256 in preference to the 2N3819. I connected the FET as per the data sheet, and it wouldn't work. I discovered that despite what the data sheet stated, the actual pin outs differed. I posted the difficulties in post 85 at the thread below, along with the PCB that I built, and posted the successful outcome at post No 95:
https://www.vintage-radio.net/forum/...ad.php?t=98221
(The mini mod still works a treat!)