DUAL GATE MOSFET...USEFUL?

[dschwartz]

I HAVE SOME MFE131 DUAL GATE MOSFETS LAYING AROUND...CAN THEY BE USED AS A NORMAL MOSFET? HOW?

[rockgardenlove]

No clue, perhaps try just join the two gates together?

[petemoore]

data sheet ?

[tcobretti]

Yeah, probably the best thing you can do is track down some data sheets for dual gate transistors and see if any of the has example applications.

[Steben]

I guess they act as normal MOSfets if you connect one pin to another. Not sure which pin to which pin and on which type of MOSfet.

There are MOSfets that have a single gate, drain, source and a bias-offset pin (the arrow which is normally connected to the source). This configures the operating point (connected to source= normal bias) and can be neat in variable biasing circuits like power sag etc...

[dschwartz]

i couldn´t find a datasheet for the MFE131......but i did find a tutorial that said that this kind of mosfet is analog to a tetrode tube..i.e a tube with two grids.......

so i dont think thay joining the two gates together will make it a normal fet...maybe it will work using one gate for signal, and the other as bias adjustment..like real power tubes (i´m getting some ideas...a power stage simulator?)

anyway..i´m not that advanced in electronics to desing from scratch a circuit with a device that i dont know for sure haw it works...

and other thingy....in every match i found about this kind od devices, it says that they are used for RF/IF frequencies...will they work as well for audio bandwith?

[Ge_Whiz]

They will work at audio bandwidths, but not particularly well. You can use them as single-gate MOSFETs by fixing the bias to one of the gates so that it is permanently 'open'. However, they are of particular interest to radio enthusiasts as 'dual-gate mixers', and as they are not manufactured anymore, they are in some demand, so you might do better to sell them.

On the other hand, they should work as dual-gate mixers at audio frequencies too, so might make for some interesting modulator effects - tremelo? Pseudo-ring-modulator?

[dschwartz]

well.. i just understood haw distortion and overdrive works...

modulation effects are, for now, a big mystery for me.. except the wah...

[DDD]

IMO useless...

[Sir H C]

From my understanding, the dual gate MOSFETs were made for RF with the idea being that in effect you have two transistors set up in a cascode.  This allows the drain on the bottom device to not move much therefore making the Miller effect minimized and so the device can be used at higher frequencies.  I guess you could do some fun stuff, drive the gate2 and then run the gate 1 from an LFO and get some tremolo effect going.  That could be cool. 

Check out the thread from zachomega about biasing, that one also is using dual gate MOSFETs.

[Dragonfly]

i couldn´t find a datasheet for the MFE131

I could....   

http://www.americanmicrosemi.com/information/spec/?ss_pn=MFE131

Not a "ton" of info, but may be useful.

AC