I could not get a MPF-102 JFET Transistor for audio pre-amp purposes, I have a K104 which they told me it is a replace of MPF-102. How can I know the pinout since there is no diafram of it on the internet anywhere thanks a lot.

 

Here ya go!
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-5/meter-check-transistor-jfet/

Generally you need only identify the gate inasmuch as drain and source are typically interchangeable...

FWIW The pinout of the k104 (flat facing, pins down) is Gate Source Drain

That said, please be advised that the K104 is not 'equivalent' to the MPF-102 -- howbeit it may work in audio applications...

Best regards and good luck!
HP

 

@Sensacell --- Please note my recent edits to post #2 -- Thanks!