Below is info taken from EKL mod sheet. It is the same as the 148GTL PC412. Hope this helps.
Rick.
Required Parts:
1 ERF-2030
1 EN-369FN
1 470pF ceramic disc capacitor
1 33K ohm, 1/4 watt resistor
Jumper wire
1) Remove L40
2) Remove C149
3) Remove R181
4) Remove TR36 and replace with ERF-2030. Note: ERF-2030 mounts identically to the removed 2SC1969. Make sure to use all the same hardware, insulator, thermal grease, etc.
5) Install jumper wire at R181
6) Add 470pF ceramic disc capacitor across C152
7) Install EN-369FN at TR36 (on solder side of PCB). Solder the positive lead (+) to the ERF-2030 gate. Solder the negative lead (unmarked) to the ERF-2030 source.

Add 33K ohm resistor (1/4 watt) from ERF-2030 gate leg to R180.
The End.