Can I replace a JFET with a MOSFET, if I account for the correct pinout?

[Bucksears]

i.e. swap a J201/2N5457 with a BS170/2N7000, if I make sure the Drain/Source/Gate are correct per the circuit design?
or is there more to it than that?

Was thinking about the BSIAB II or Dr. Boogey for starters.

Thanks
- Buck

[duck_arse]

the mosfets will need a bias voltage, the jfets are most often self-biased via a resistor to ground from the gate (though they can also use fixed bias).

search up joe davisson circuits, he's already done most of them.

[R.G.]

What he said.

JFETs are (usually) depletion-mode devices, which means if you do nothing to the gate-source voltage, they conduct as much as they possibly can. You have to do something to the gate to turn it OFF.

MOSFETS are usually enhancement-mode devices like bipolar transistors - they normally don't conduct at all, and you have to do something to the gate-source to turn them on a bit.

The "usually" in those sentences is there because some few, rare examples of both may be made in a way that makes them less depletion or enhancement. Particularly with MOSFETs, you can have enhancement mode or depletion mode, and some few are conductive, but not hugely with Vgs=0V. You are unlikely to run into any of these exceptions unless you go looking for them.

[Transmogrifox]

You are unlikely to run into any of these exceptions unless you go looking for them.

That said you might have some success experimenting with depletion mode MOSFETs.

My intuition tells me you may be able to find a depletion MOSFET able to give you more gain given similar bias conditions.  This is the main benefit I can think of.

Also as duck_arse hinted you could re-use the basic design concept if you make a bias for the MOSFET stages.  This is something you could not do in a tidy fashion on an existing layout or PCB but it's something you could easily do on a breadboard and also plan into a revised layout which allows for either type of device.

[mac]

If you want to use mosfets because they have more "gain" than the fets you mentioned above, try toshiba 2sk117 or similar. Half way between mosfets and j201.

mac