BSR58 JFETs, can they be used?

[bushidov]

Hi Guys,

Just a quick question. I know these are surface mount, but surface mount soldering is something I do a lot of, so that doesn't bother me. But I was wondering with a lot of these J201 designs where they take a tube-amp's preamp section and change the tubes out with J201s, or even something as simple as a Tillman FET preamp, could one substitute a BSR58, if the pinouts are made to work?

Here's the datasheet on this part:
https://www.digikey.com/product-detail/en/on-semiconductor/BSR58/BSR58CT-ND/3042770

I ask, because what I really am trying to say is I don't know what I am looking for in the datasheet to know if this will work.

And in case, no one is familiar with a Tillman FET preamp:

[antonis]

Here's the datasheet on this part:
https://www.digikey.com/product-detail/en/on-semiconductor/BSR58/BSR58CT-ND/3042770

what I am looking for in the datasheet to know if this will work.

Another datasheet which declares something about transconductance (forward transfer conductance)
(ON & Small signal characteristics..)

[merlinb]

The deciding factor where JFETs are concerned is usually Vgs(off). That's the first thing you want to look at, everything else is secondary. The J201 is unusual in having a very small Vgs(off) rating, and a very narrow spread, only 0.3 to 0.8V.

The BSR58 quotes: 0.8 to 4V. Some some BSR58s will work pretty much the same as some J201s. If you test your BSR58s and select the ones with the smallest VGs(off) (like less than 1.5) then it should work OK in the Tillman. Trim the source resistor to suit.