Question about Jfet! j201

[askwho69]

Hi Again i have a question about Jfet!

1.) how can i identify if its a high gain jfet? sample j201?
2.) some people says that j201's sub is sk117, 2n5457-2n5458, 2n5484 etc...
3.) if ill sub the j201 to 2n5457-58 does it affect the gain? and the bias? example is amp simulator overdrives.. Boo, Marshall jcm plexi etc . .
4.) can j202 can be a substitute? is this has better gain?
5.) Thank you!

A2

[edvard]

Generally, and I do mean GENERALLY, the lower the Gate-Source cut-off voltage and the greater the Forward Transconductance (noted on most datasheets as VGS(off) and gfs, respectively) the better it will amplify.
The J201 has a typical VGS(off) of -0.3 to -1.5 and a gfs of 500 and it amplifies wonderfully.
A 2N5457 has a wider variance; VGS(off) of -0.5 to -6.0 but a gfs between 1000 and 5000 with no "typical" values.
The J202 runs a VGS(off) of -0.8 to -4.0 but a gfs of 1000, so which one is better?
Breadboard it and find out.

The J201's have been time-tested to work well, be fairly consistent (always a benefit when working with JFETs), and have decent gain.

[askwho69]

ohh! this a good explaination you have there mate.. thank you so much. . . i did understand but needed something also that everyone tried thank you

A2