Differences between varieties of 2SK30 JFETs?

[Mark Hammer]

I have an easy time picking up K30AY transistors at reasonable price, but keep seeing these "select" SK30ATM-GR FETs pop up in various schematics, such as older Roland/Boss phasers and such.

Anybody know what the difference is between these GR types and the regular K30s?  Are they matched to some spec?  units that are guaranteed to fall within a certain range of the overall K30 spec?  Can a person with enough "regular" K30s on hand find some GR types in there?

[analogguru]

I have hundreds of -GR, could I find -Y types in it ?
A look at the datasheet gives the answer (at the bottom of the first page):
http://www.synthdiy.com/files/2007/2sk30atm_en_datasheet_030325.pdf

Idss classification: .... -Y: 1,20 ~ 3,00  -GR: 2,60 ~ 6,50

analogguru

[Mark Hammer]

A-ha!  Thanks for that.  So there is a chance that I may be in possession of some K30s that meet the GR spec.

Question:  How would I measure drain current, and what would I need to do that?  Would it be something as simple as the setup for matching JFETs on Vgs?

[B Tremblay]

Mark, you can use this circuit to find Vp and Idss of FETs: http://runoffgroove.com/fetzervalve.html#11

Here's a Japanese datasheet that outlines the different suffix meanings: http://www.synthdiy.com/files/2007/2sk30a_japanese.pdf

I'd like to find some 2SK30AR to compare with J201.

[Gus]

IDSS 9VDC supply, meter set to current in the + leg to the drain, gate to source to ground, connect other meter leg to +9VDC.  that is the IDSS at 9Vdrain source.  If the jfets are from the same batch the other parameters should be close.  I would select for what parameter is more important.

[greaser_au]

Idss is the maximum 'natural' flow of current through the JFET channel with no other influences, i.e. zero gate bias.

I (current) ds (drain to source) s  (gate shorted -  typically the last letter in a 4 letter parameter refers to the connection 'status'  of the remaining terminal)

In theory you could use a very direct method and measure it by shorting the JFET's G & S terminals, and  connecting your multimeter (on mA range) to a 6V or 9V (stay below the FET's Vdgs) battery with the JFET in series between them (D to battery +). This IS NASTY, & carries a risk of toasting your multimeter if the device is shorted or you mess it up.  Better would be to use a small, say 100-1kohm resistor in series. Ohm's law still applies, & using a too-large resistor may swamp your test;   e.g. using a 9v battery to test a device with an Idss of 6.5mA (max for GR spec), would drop 6.5v across a 1k resistor leaving 2.5v across the FET- probably ok, but if you were using a 6V battery for the test...  

As an aside the various spec range letters used to be painted/inked colour codes on the devices: GReen, BLue, Red, Orange, Yellow

[mac]

I have the datasheet of those Toshiba 2sk30atm.
I do not think they are similar to  J201, higher Vgsoff and possibly less gain.
Toshiba 2sk117 have low Vgs and more gain than J201. Same idss classification as 2sk30.

mac

[R.G.]

The "GR" and "YL" (which stand for "green dot" and "yellow dot") subgroups are sub-bins of devices sorted by Idss.

Since Idss is linked to Vgsoff, it's also a sort for how much voltage is needed to either get the device into the linear resistance/triode region or turn it on/off as a switch.

Hence specification of a particular group.

J201 is NOT similar to the 2SK30 excepting they're both JFETs.

[arawn]

Thanks mark this seems to havebeen quite educational and everyone whio has contributed wow!

[Mark Hammer]

That it has, my friend.

I'm looking forward to checking out the K30s in my bin.

[marsen]

So what the IDSS classification affect to our applications?

[R.G.]

So what the IDSS classification affect to our applications?

Idss, transconductance ("mu"), and Vgsoff are related by the physics of the device. Picking an Idss group limits the variations of the transconductance and Vgsoff.

[mikro]

So what the IDSS classification affect to our applications?

Idss, transconductance ("mu"), and Vgsoff are related by the physics of the device. Picking an Idss group limits the variations of the transconductance and Vgsoff.

What happens if I use a JFET marked "Y" in a circuit that needs a "GR" according to the schematic?

[J0K3RX]

2SK30ATM

IDSS classification / R: 0.30~0.75 / O: 0.60~1.40 / Y: 1.20~3.00 / GR: 2.60~6.50

2SK30A-R are comparable to J201's but with less noise and are about as hard to find as Bigfoot riding a Unicorn...

Also, they are the exact same spec as 2SK208 and 2SK879.


2SK208-R are commonly used in almost all of the AMT Electronics JFET preamps.


You can find both on ebay but you will be hard pressed to find any with the "R" idss drain current rank.

[kingswayguitar]

Better would be to use a small, say 100-1kohm resistor in series.

I find even 100R to be a bit high.  I bought a super accurate 1W 1ohm resistor especially for this purpose.

[greaser_au]

Better would be to use a small, say 100-1kohm resistor in series.

I find even 100R to be a bit high.  I bought a super accurate 1W 1ohm resistor especially for this purpose.

Strewth...  this is an old thread...  that one must have been my first post on this forum!!!

david

[kingswayguitar]

Better would be to use a small, say 100-1kohm resistor in series.

I find even 100R to be a bit high.  I bought a super accurate 1W 1ohm resistor especially for this purpose.

Strewth...  this is an old thread...  that one must have been my first post on this forum!!!

david

Cheers man!!