JFET tests good, no longer works in phaser

[Mad Dave]

Built a P45 clone (Madbean Smoothie) a few yrs ago. At some pt I started asking myself whether it was working right. I knew it was subtler than a P90, but it didn't seem right, so I quit using it.

I'm working on another phaser build, and I thought I'd try matching my own JFETs. (Previously bought matched pair of 2N5458s from GGG.) Built the tagboard Greatly Improved JFET Matcher II, and fooled around testing the few JFETs I had on hand, also measured the ones in my P45/Smoothie.

Though the ones in my Smoothie test OK (~0.740V), one of them doesn't work in the circuit. If I swap it w/ one of the ones I had on hand (that tests similarly) the P45 works like it's supposed to, and like I remember it working. (Also works w/ another pair of 5485s I matched up.)

Is this JFET tester not testing what it should be testing?  Thanks.

[jkokura]

Not all JFets these days are real. I have About 1000 fake 2N5952s from a coupe different suppliers. Also, transistors are fickle, and finicky. Sometimes they just don't work, or they fail. It's not common, but it can happen.

Where did you get your jFets from?

Jacob

[Mad Dave]

Where did you get your jFets from?

Tayda.  They're the same brand (they have a big F on them) as the matched pair I got from GGG (one of which failed).

Gonna have to buy 'em in bulk, as I need 6.  Working on a Maestro PS-1.

[galaxiex]

The "F" is for Fairchild Semiconductors and there's a lot of fakes out there these days.

Buy from reputable sources. 

[Mad Dave]

The "F" is for Fairchild Semiconductors and there's a lot of fakes out there these days.

Buy from reputable sources. 

Yeah, there's no way these are genuine Fairchilds. I didn't realize they used that "F." I'm more familiar w/ their other logo.

Thanks for the info.

[galaxiex]

Are you a member at GuitarPCB?

http://www.guitarpcb.com/

For the link below to work you need to be a member. (it's free)

Here is some info and pics of fake and genuine Fets.
Scroll down the page.... 

http://www.guitarpcb.com/apps/forums/topics/show/13285269

[devilsnight]

I like buying in bulk from tayda also, and have never noticed any quality issues.  I noticed recently though that smallbear seems to have jfets in stock for pretty much the same price. They seem to have a pretty high standard from what I hear also. Seems like it might make sense to buy transistors/ic's/etc from them? I have a p90 board I've been wanting to build for a long time so I've been kind of up in the air on matching them myself or buying a matched set from somewhere..

[Mad Dave]

Cool, thx. The JFETs I've got sure look a lot like the genuine Fairchild.

I hadn't been a member over at GuitarPCB, but it looks like a good site. Thx for hipping me to that, too.

Are you a member at GuitarPCB?

http://www.guitarpcb.com/

For the link below to work you need to be a member. (it's free)

Here is some info and pics of fake and genuine Fets.
Scroll down the page.... 

http://www.guitarpcb.com/apps/forums/topics/show/13285269