High Current MosFet selection for First Watt F5

[Uunderhill]

The schematic for the First Watt F5 shows an IRFP 240 and IFRP 9240 in the output stage.

However, continous Id = 12 Amps for the IRFP 9240 p channel MOSFET.

Other DIY'ers have suggested Toshiba 2sk1530 / 2sj201 or 2sk3497 / 2sj618 partnerings.
However, these are also limited to 10 or 12 Amps.

Vgs(off) is between 2v to 4v for all of these Mosfets.


Gamut Amplifiers also use a single Mosfet pair per channel, but have much higher power ratings.
Also, what I consider to be important - very low output Impedance.


Years ago I designed a 1 hp DC motor speed controller with a FB180SA10 Mosfet.
This beast can handle 120 Amps @ 100 oC with a channel resistance of 0.0065 Ohms.

One possible p Channel Mate is a IXTN90P20P, rated at a meager 90 Amps @ 25 oC.

Both these MosFets also have a Vgs(off) between 2v and 4v.

The problem is they are about $35 each.


Does any one have any other suggestions for high current Mosfet's for a First Watt F5 ?