This is a minimal oscillator that can be made with just two components. I have tried several N type depletion mode jfets but the mpf102 and j310 I had on hand, worked ok, with the j310 to give more power output, about 4vpp at 1Mohm without significant distortion. I did not have the bf245a on hand to try. I used a t50-2 toroidal core with 13t in total and about 3-5T for the tap, which gave about 21.5MHz. At 4T for the tap, the output voltage was lower but the oscillator could work from 4-6V, with varied output power (max 1vpp at 1M). At the 5th turn tap, the oscillator worked only on 3v but with about 4vpp at 1M.