Have a go with RD16HHF instead of the IRF.? Works for me, The leads are different so beware..
I have added a socket to one board with 4 holes. The 4th extra is soldered to the gate line closest to 2219. There is a convenient track there. Only that I have to plug in the RD16 reverse and one pin to the right.
I'm sure you will get a better response at the output.
Raj
At 15-11-2017, you wrote:
Richie, it sounds like yours will work fine at higher frequencies since it's designed that way- or at least I'd assume so.