Attention Jfet Phaser intellects!

[njkmonty]

I have recently built a phaser which my son like so much he wanted me to build him one too
the only problem is, that the jfets i bought i think turned out to be fakes. After buying some more the new batch  dont work and measuring completely different
so i dont know what they really are.
I was wondering if anyone could assist how to identify or use the info i have to find something similar?
using my chinese $7 component yellow box


they come up as a NPN transistor with hfe 96.8K!  vf 469mv
so i used my RG jfet tester and got a reading range of -0.13   to -0.2 on my working jfets

on page 13 and 14  is a good little comparison chart of some jets
can anyone assist / advise  what alternatives that  may be suitable?
is it the VGS(off) mins and maxs i should be looking at?
http://www.mouser.com/catalog/supplier/library/pdf/fairchildsmallsignal.pdf

[duck_arse]

more info please - what parts did you put in the working phasor phaser, what parts have you sourced that aren't as you think? most importantly, what do your "bad" fets say when R.G.'d?

this just in: which phaser circuit?

[anotherjim]

Seems to me they're testing as very leaky Ge transistors!
What were they supposed to be?

[njkmonty]

roland phase 5
2sk30

i originally got the working ones about 3-5 years ago from futurlec, recently got some more from them  and completely different to new offerings
will R.G.'d  the new batches  results shortly

[duck_arse]

K30A - check your pinout. again. I'll just leave this here, y'no, just in case .....

[njkmonty]

yeah pinout is fine

[njkmonty]

anyone??

[Slowpoke101]

Here you go..

[njkmonty]

is that what this symbol means?

as stated earlier i have jfets which aren't what they are labelled , they  come up as npn transistors when tested, all the others ive bought which measure as 2sk30 measure as intended.


im trying to use the little information i have  using the geofx testing reults etc to work out their specs so i can possible look at ordering something with similar specs
5457
j201
j112
5452  etc i have on hand all dont work,  is there a way of identifying jfet  specs another way?


here is its readings
and here is a pic of the jfet

[Slowpoke101]

Ah...Idiot here thought that you were after the 2SK30 pinout Sorry.

I have the exact model component tester that you have and another one (but different ) that I built.
Both can get rather confused with JFETs and think that they are testing a standard transistor.
But when testing my current stocks of 2SK30 JFETs both testers do show that the device being tested is a N channel JFET. But I am testing 2SK30A GR devices which usually have a higher Idss than the Y type. This difference seems to be the thing that causes these little testers to work or not work. Also the data that they display when they do work with a JFET is not very reliable nor believable.

The geofx tester is a great way to test a JFET and I use it often but only to test Vgs. Drain current is another reading that can help with matching.

[njkmonty]

the range using the jfet matcher  ive been getting is...
-0.140   to -0.150

where 5458's are giving me  -1.69
real   2sk30a are                 -0.825
         j112                           -3.05
          5452                        -1.724
so as you can see the fake ones that funnily enogh work great are getting very low
readings , and its trying to use this info to select an alternative?

[Slowpoke101]

My test results using the geofx tester when testing a 2SK30A GR is;

  Vgs = -1.320V  (which is about what I would expect )

I'm not set up at the moment to test Idss but give me an hour I can do so.

But the LCD tester (same as yours ) shows;

  Vgs = 0.82V
     I = 1.2mA

So I can't really believe that what the tester is indicating is correct.

[temol]

From my limited experience with measuring jfets - forget about using this component tester (I have a similar unit and readings are not reliable). Use battery and multimeter.

T.

[Rob Strand]

From my limited experience with measuring jfets - forget about using this component tester (I have a similar unit and readings are not reliable). Use battery and multimeter.

I'd go back to basic pin identification measurements and use a multimeter to identify the pins.

Use the diode function to find the common pin which gives a voltage reading of around 0.6V (normally within 0.55 to 0.75V) to the other two.   For NPN BJTs and N-channel JFET the diode's anode should be the common pin.  That would be the base or gate.   Now switch to 2k ohms range and measure the resistance between the *other* two pins.  If you get a reading in both directions say less than 1k then it's a JFET, if you don't get any reading at all then it's a BJT.

For the MOSFET case there will be a common pin which gives no reading to the other two (for both polarities).

Once you do that see what matches up with the pin-outs you have and what your gizmo says.

Oh, there might be a software update to the gizmo that comes-up with "Fake"  .

[njkmonty]

Diode test:

Red - Green : nil
Green - Blue : 0.675
Red - Blue : 0.25

resistance test:
Red - Green : nil
Green - Blue : 475K
Red - Blue : nil

$7 yellow box says the following:

NPN
RED - Collector
GREEN - Base
Blue - Emitter

hFE = 85.9K
Uf = 464mV

[duck_arse]

I'd think any bjt indicating a gain of 86,000 would be iffy, one way or another. and if I thought I was testing a jfet that read as a bjt, with an hFE of 86k .....

I've never had one of those boxes to test with. an R.G-o-Meter has always done the good thing.

[nickbungus]

Ducks arse, which rgmeter have you had most success with?   I've built a few of the online fet testers and have had very inconsistent results.  I've measured them once then gone back to them and obtained different results.   I've also got one of those yellow boxes and haven't had that problem but I'd like a bit more granularity.

[duck_arse]

sorry, got my -o-Meters confused. this is the ROG, the one I've used most often:


I think there is another, possibly an RG, that uses an opamp, but I couldn't see it when I searched my local files.

[Rob Strand]

Diode test:

Red - Green : nil
Green - Blue : 0.675
Red - Blue : 0.25

resistance test:
Red - Green : nil
Green - Blue : 475K
Red - Blue : nil

The 0.25V is an odd value.  Like it could be germanium but that's inconsistent with the 0.675, unless it's a Darlington germanium which is extremely unlikely.  Then there's the possibility there an internal resistance across Red-Blue but that's inconsistent with the resistance test.

My best guess at this stage is it's an NPN transistor.
blue = base
green = emitter  }  these could be flipped but that's my best guess.
red = collector   }

$7 yellow box says the following:

NPN
RED - Collector
GREEN - Base
Blue - Emitter

I suspect it's confused since GREEN-base is not consistent with your manual test.  That's backed up by the very high gain value which I suspect comes from a heap of current going down whatever lead the box uses to measure current.

I'm also confused but not as much as the box.

It would be very useful to wire up something like this tester:
https://cdn.hackaday.io/images/4589791484797920897.png

You don't need the diode part and the 9k, and a 1M is fine for the 900k.  Replace the 1mA current meter with a 220 ohm resistor and measure the voltage across that resistor;  *roughly* 100mV is hFe=100.  As an additional sanity check to make sure the base current has an effect on the collector current I'd do a second check with the 1M replaced by 470k.  You should see double the current.

If you get low gains try flipping red and green.

[njkmonty]

i began breadboarding those 2 circuits but got quickly frustrated!
I went back and read over the post.

it just occured to me that pending the diode tests probes orientation can give different resuilts!
Doh!
heres what i got second time round
Diode test:

Red - Green : 0.675
Green - Blue : 0.675
Red - Blue : 0.25

i have paused on pursuing the transistor testing for the moment hoping that this new info may refine what to do.
what is strange is this transistor works great in this phase pedal!

just the hassle to identify what it is or what it may be similar too!
here is the jfet geofx tester results