Transistor Pinout Question

[soupbone]

I saw somewhere on here that someone posted about transistor pinouts,but I can't find the post.Whoever it was,showed how to map drain,source,gate to collector,base,emitter.I'm trying to find how they match up,so I can try out different fets.Any help would be gladly appreciated!

[nocentelli]

Very crudely, for npn bjts (e.g. 2N3904) compared to N-JFETS (e.g. J201), bjt collector = drain, base = gate, emitter = source. This is in the sense that in most guitar circuits using these parts as a gain stage, the guitar signal goes to base/gate, emitter/source is connected to ground (usually with a resistor and maybe cap), and the amplified signal output, and positive power voltage connection is made via collector/drain. Additionally, they are sometimes both biased with a vref applied via base. In a buffer, both bjt and n-jfet can be used with input and bias voltage to base/gate, 10k or so emitter/source resistor to ground, collector/drain direct to +9v and buffered unity signal taken from emitter/source.

However, they are not generally interchangeable: i.e. one cannot drop in a FET where a bjt is specified and expect it always to work since they are biased in different ways, using different sets of rules. Sometimes tweaking values will help, but this is more blind experimentation then rational scientific design.

[soupbone]

Very crudely, for npn bjts (e.g. 2N3904) compared to N-JFETS (e.g. J201), bjt collector = drain, base = gate, emitter = source. This is in the sense that in most guitar circuits using these parts as a gain stage, the guitar signal goes to base/gate, emitter/source is connected to ground (usually with a resistor and maybe cap), and the amplified signal output, and positive power voltage connection is made via collector/drain. Additionally, they are sometimes both biased with a vref applied via base. In a buffer, both bjt and n-jfet can be used with input and bias voltage to base/gate, 10k or so emitter/source resistor to ground, collector/drain direct to +9v and buffered unity signal taken from emitter/source.

However, they are not generally interchangeable: i.e. one cannot drop in a FET where a bjt is specified and expect it always to work since they are biased in different ways, using different sets of rules. Sometimes tweaking values will help, but this is more blind experimentation then rational scientific design.

Great!Thanks for the info!