2N5457 vs. 2SK117 in a Fetzer Valve

[mordechai]

I've used some 2N5457's in a two stage Fetzer Valve before, and like how they sound.  Nice breakup and drive.  But, recently I stumbled across a fairly decent batch of 2SK117 JFETs (50 of them).  I don't know nearly enough about these other than that they were used in the discrete opamps in the Boss BD-2, and that they have different pinouts than the 2N5457...and that they have low noise specs.

Are these devices possible candidates for substitution?  Do they have sufficient gain to work in a Fetzer circuit (if, for example, I lower the value of the source resistor to up the gain)? 

[KarenColumbo]

I'd say pop them in and bias them with pots/trimmers instead of resistors until they sound nice

[JebemMajke]

Last time i used 2sk117 it yielded more gain than j201.

But i guess with a gain trimpot, or pot, it is fine.

I prefer bf245b for one-two stages of jfet type boosters/preamps.

[Jeema]

It can totally work, but like the previous poster said, it will probably have more gain.  That's because it has a higher transconductance judging from the datasheet info.  Biasing will be different too.  I'm guessing you'll probably need smaller resistor values for both the drain and source to achieve the same quiescent bias point and gain of a 2n5457 circuit.

[MaxPower]

Isn't the point (of the fetzer valve) to measure the Vgs(off) and Idss of the Jfet that's going to be used, and then bias it to be in it's "tubey" range? So even if you use another JFet of the same type (part #), chances are the VP and Idss will be different and the biasing resistors will need adjusting.

[mac]

Last time i used 2sk117 it yielded more gain than j201.

I agree.
"Gain" is halfway between a j201 and a mosfet.
And Vgsoff is low too, 0.5v average.

Whenever I need a "regular" fet, 5457, bf245a, I use 2sk246 from Toshiba too.

mac

[mordechai]

Isn't the point (of the fetzer valve) to measure the Vgs(off) and Idss of the Jfet that's going to be used, and then bias it to be in it's "tubey" range? So even if you use another JFet of the same type (part #), chances are the VP and Idss will be different and the biasing resistors will need adjusting.

Well, I'm just using trimmers to bias the circuit, so I can pop in a 5K Trim to handle the 2SK117 and get it to function properly.

[JebemMajke]

2sk30A is a great one as well.