Testing my Grab Box JFETs

[flemming]

Pulling together a couple of threads here for no particular reason other than I spent a bunch of time testing JFETs and felt like I should do something with that info. In the Small Bear Grab Box thread I mentioned that I got a bunch of JFETs and @bowanderror said that I probably made out better than I thought. I've only built a few pedals that required a JFET or two, so I'm green on this topic. I put together the runoffgroove tester using this vero layout, but modified it a bit by integrating a slider switch and a push button for power. This is easy enough to breadboard as needed, but doing the job once is probably worth the effort.



In my grab box I received a mixture of 2SK19, 2SK30, and 2SK30A JFETs. I loosely borrowed this spreadsheet layout and I'll attached my complete results, but the averages were:

	Measurement		Calculated
	Vp (V)	Idss (V)	VGS(off) (V)	Idss (mA)	Rs (Ω)	Rd (Ω)	RDS(on) (Ω)
2SK19-GR	2.936	.844	-2.94	8.44	289	333	174
2SK30-GR	2.051	.411	-2.05	4.11	415	1-74	250
2SK30A-D	1.301	.215	-1.03	2.15	503	2681	303
2SK30A-R	.616	.052	-0.62	0.52	986	13483	594

Everything appears to be within spec (until someone tells me that my test/math was bad). There are certainly some that could be matched up in pairs or maybe even quads depending upon the tolerance. I couldn't find a datasheet for the 2SK30A with a "D" Idss bin. From my tests, these appear to match up with what would be expected in the "Y" bin, so I guess if you're building a Low Tide let me know. Most of the 2SK30A-R's appear to match up with what would be expected for a J201 so I assume I can try those out as substitutes if need be.

 

[bowanderror]

Glad to see they all tested OK! It's definitely worth measuring these now, it'll make life so much easier down the line. With the increasing difficulty of finding real JFETs, I'm sure they will be useful, even if just as a sub for other JFETs.

I can confirm that your "2SK30A-D" is a likely 2SK30A-Y. Here are some actual -Y versions tested in the same tester you used:


Along with 2SK30A-R as a sub for J201, you can use the 2SK30-GR as a sub for 2N5458 & 2N5457. Your posted measurements cover most of the range that my through-hole & SMD version tested. I'd use the higher range ones for 5458 and lower range ones for 5457.

Those 2SK19-GRs are a bit of an oddball as I hadn't actually run in to them before. According to my limited JFET spec comparison spreadsheet, they look like a good substitute for BF245B, BF256B, and MPF102. The datasheet specs are in white, and I added your avg measurements to mine (in the green columns):

 

[Coda]

Question: in the runoutgroove schematic, is there a junction where there two resistors and lug 2 of the toggle meet?

 

[fig]

This may help..

 

[Coda]

Question: in the runoutgroove schematic, is there a junction where there two resistors and lug 2 of the toggle meet?

Nvm. I figured it out. No wonder I could never get this to work…

 

[fig]

Well, I just reposted what you did. Duh fig. Apologies sir. Sometime I wonder about me.

 

[Coda]

Well, I just reposted what you did. Duh fig. Apologies sir. Sometime I wonder about me.

I ignored your post so as to not draw attention to your shame…

 

[fig]

I ignored your post so as to not draw attention to your shame…

What post? Oh, must be one of mine. I've had me on ignore for several months. I can't take my incessant ramblings.

 

[TravisM]

I've had me on ignore for several months. I can't take my incessant ramblings.

Seems like the only prudent thing to do.