Looking for help with JFET basics here.

I have J112, how do I calculate a basic common source circuit?

From simple research I found this: we care about two important parameters:

Idss - current that goes freely through the JFET (from Drain to Source) if there is no voltage applied to the Gate, called "zero-voltage gate current"

Vgs(off) - voltage applied between Gate and Source that will prevent JFET from conducting any current from its Drain to Source, called "gate-source cutoff voltage"

Looking at the J112 datasheet from onsemi we have two graphs. Why is there 0-40mA and 0-15mA scales?

For some reason it is considered a good practice to take Idss for a given JFET and use half of that. Why?

Assuming J112 Idss = 5mA, we are aiming at 2.5mA.

If dual power supplies are +-15V, we have drain resistor Rd = 15V/2.5mA = 6kOhm.

Looking at the graph we can match 2.5mA to Vgs around -0.3V.

Now, this is the part where I don't know how to continue to calculate source and gate resistors because it is dual supply.

Any help is much appreciated!

I have J112, how do I calculate a basic common source circuit?

From simple research I found this: we care about two important parameters:

Idss - current that goes freely through the JFET (from Drain to Source) if there is no voltage applied to the Gate, called "zero-voltage gate current"

Vgs(off) - voltage applied between Gate and Source that will prevent JFET from conducting any current from its Drain to Source, called "gate-source cutoff voltage"

Looking at the J112 datasheet from onsemi we have two graphs. Why is there 0-40mA and 0-15mA scales?

For some reason it is considered a good practice to take Idss for a given JFET and use half of that. Why?

Assuming J112 Idss = 5mA, we are aiming at 2.5mA.

If dual power supplies are +-15V, we have drain resistor Rd = 15V/2.5mA = 6kOhm.

Looking at the graph we can match 2.5mA to Vgs around -0.3V.

Now, this is the part where I don't know how to continue to calculate source and gate resistors because it is dual supply.

Any help is much appreciated!