Replacing transistors

[seanm]

I would like to replace an NPN transistor with a FET in an input buffer. The NPN goes BCE so the FET needs to be GDS (or SDG). However, every FET I can find is GSD!

So, does anybody know of a good FET replacement that is GDS?

Or a slick way of swapping transistor leads, maybe via a socket?

[seanm]

Wrote too soon. It looks like a 2N4416A would work. The data sheet says it is for "general purpose amplifier and chopper applicatons".  Anybody know about this transistor?

And if it won't, I think I can stick the leads from the drain and source into the current holes, then solder a wire back from the gate to the correct hole. There is lots of room for this mod.

[R.G.]

Unless you also change some parts to redesign the biasing, it's unlikely to work correctly.

NPN's are enhancement mode devices - meaning that they don't do anything until you force current into their base.

n-channel JFETs are depletion mode devices - meaning that they conduct all they are capable of until you back bias the gate to turn them slightly off.

Merely subbing one for the other without changing the bias arrangements usually forward biases the gate-channel junction and nothing much happens.

Pinout of EBC, ECB, etc or GSD, GDS etc is not a problem. Just get your needle nose pliers and bend the leads around in midair to the correct order. If you are concerned about shorting, slip little lengths of insulation stripped from insulated wire over the leads before inserting them in the holes.

[seanm]

Unless you also change some parts to redesign the biasing, it's unlikely to work correctly.

I am planning on doing this. I was too late today to get the transistor, so now I have to wait until monday

Pinout of EBC, ECB, etc or GSD, GDS etc is not a problem. Just get your needle nose pliers and bend the leads around in midair to the correct order. If you are concerned about shorting, slip little lengths of insulation stripped from insulated wire over the leads before inserting them in the holes.

Ok, I will try that. The pins on the original transistor are inline and, yes, I was worried about shorting.