Are these 2SK170 JFETs genuine? - Page 1
Forum section: electronics / beginners

author: Frankentronics
author_rank: Regular Contributor
timestamp: January 04, 2018, 02:43:35 pm
content: Greetings,I bought some 2SK170 JFETs on Amazon (other suppliers no longer have them in stock).When I test them on my component tester I get two different readings. So, I don't know if half of them might be fake.One reading shows a JFET icon and the other reading shows a JFET with a diode between Source and Drain.I'm attaching the photos.What do you guys think?Thanks...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 04, 2018, 07:26:14 pm
content: I would be more worried about being shorted the noise figure than DC parameters. There's very little difference between JFETs of the same size: mainly what you're paying for, is some set of qualified parameters, whether it's noise and gain (like this one), or RF or switching parameters (other types).If all you have to measure is one of those toys...Huh... I wonder if a noise figure test could be programmed into one of those. Hmm. Probably not, not enough gain between DUT and ADC input I would guess, in addition to the difficulty of biasing.Tim

author: zike
author_rank: Contributor
timestamp: January 04, 2018, 08:10:49 pm
content: Not familiar with your test rig, but anyway it is quite possible those are fakes, particularly if they were bought in bulk for a low price. Checking I_DSS is a first cut, but even if they pass, you still won't know unless you do a detailed noise characterization. In fact I received a batch of 2SK170 and 2SJ74 that were obviously counterfeit, as with only one exception they all fell outside the allowable I_DSS range for genuine parts. Your counterfeiter might be smarter than mine was ;^)Best way to know, is to buy from a current maker. Linear Integrated Systems produces true equivalents in California under part number LSK170, in 3 sorted I_DSS ranges (and in SOT-23 packages as well as TO-92). You can get small quantities from Trendsetter Electronics, e.g.here.They cost a few bucks, because theyshould.

author: floobydust
author_rank: Super Contributor
timestamp: January 04, 2018, 08:14:54 pm
content: Your tester is giving weird numbers, Id=0.82mA at Vg=0.58V, and one test VDS is 4.59V.None of the datasheet curves are near those values. For the 2SK170, it has two rankings, IDSS GR: 2.6-6.5mA and BL: 6-12mA.I would measure IDSS to see what you get, as a first test.Linear Systemsremakes many JFETS, changing the usual 2SK prefix to LSK. They offer LSK170 and LSK170X-1 low noise, high IDSS version.

author: sdouble
author_rank: Frequent Contributor
timestamp: January 05, 2018, 06:44:13 pm
content: n-channel j-fet, Vgs should be negative.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: January 05, 2018, 07:14:44 pm
content: You can get genuine lsk170 jfets from the diyaudio store. They are from Linear, graded by Idss.ampslabs sells NOS Hitachi '170s.http://www.ampslab.com/trans_2sk170bl.htmI have 10 left over from a previous project if you need some. PM me.

author: floobydust
author_rank: Super Contributor
timestamp: January 05, 2018, 10:16:00 pm
content: Quote from: sdouble on January 05, 2018, 06:44:13 pmThese $20 testers only have 5V power, there is no negative rail so they cannot cut off a JFET.That, and the strange low ID and VGS number they spit out for any JFETS, these testers are not good for measuring these parts.

author: Zero999
author_rank: Super Contributor
timestamp: January 06, 2018, 02:13:41 pm
content: Quote from: floobydust on January 05, 2018, 10:16:00 pmIt's true that those cheap testers are only single rail, but it's untrue a negative rail is required to cut-off an N-channel J-FET. Hold the drain at +V, the gate at 0V and sweep the source voltage and the gate-source voltage will negative. The drain current current can be then plotted. See attached simulation.

author: floobydust
author_rank: Super Contributor
timestamp: January 06, 2018, 05:17:49 pm
content: I did realize you can make -5V bias as a second point on the curve. But I don't see any useful test numbers on my AY-AT as well, trying some JFETS.$20 testers have no DAC, only two resistor values switched at each Mega328 pin, 680R and 470k.I expect an IDSS value at 5V and 680R, and ID for VG=-5V, but that gets confused if it sees a near a diode drop for VDS and then assumes a diode exists?So this would be a AY-AT firmware issue I guess.

author: Frankentronics
author_rank: Regular Contributor
timestamp: January 06, 2018, 06:34:12 pm
content: Thank you all again for your replies.I see, again, how much I have to learn before I can say that I understand electronics. I had no clue what IDSS meant... So, I found this thread:http://stompville.co.uk/?p=112Quote from: floobydust on January 04, 2018, 08:14:54 pmI think there's something wrong with their site. The "purchase" links (for any products) don't work.Quote from: RandallMcRee on January 05, 2018, 07:14:44 pmThanks for the offer. At this point I should first test them properly and if they don't check out I'll contact you. Thanks...

author: Frankentronics
author_rank: Regular Contributor
timestamp: January 06, 2018, 06:39:02 pm
content: Quote from: floobydust on January 06, 2018, 05:17:49 pmDo I understand correctly. That reading that shows a JFET with a diode is most likely a firmware issue, correct? In other words, there is no such electronic component that would have a JFET with a diode between D and S, correct?

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: January 06, 2018, 07:03:09 pm
content: QuoteLinear Systems does not sell to individuals. That is why myself and other helpful individuals pointed you to Texas Components. I noted that they sell for quite a bit more than some other sites like diyaudio and ampslabs.Sigh. You do need to read in order to help yourself.My experience (and many others) has been that ordering semiconductors off ebay never saves money if your time is worth anything. Anything at all.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: January 06, 2018, 07:10:40 pm
content: Sorry, I meant to make this point earlier, but forgot--Really the main reason to buy an 2SK170 jfet in the first place is because they have premier noise specs. Is that why you want them?If not, you are wasting money. Its yours to waste and, if this is the case, ignore everything further.If the noise specs concern you then you are truly wasting time and money by not buying from some known, good, source--because you obviously don't have the technical ability to measure their noise parameters. Its difficult. Ebay sellers know this and substitute cheaper jfets not screened for noise. Caveat emptor.

author: floobydust
author_rank: Super Contributor
timestamp: January 06, 2018, 07:48:16 pm
content: Quote from: RandallMcRee on January 06, 2018, 07:03:09 pmI emailed LS sales in California, they were fine to do a quotation and credit-card order. I think their website store is broken.Ended up getting LSK JFETs fromTrendsetter in Texas, said they had stock, but no they had to order them in from LS CA.I wouldn't trust any eBay stuff. For the $5 you might save, the JFET is probably working with time, sweat and equipment worth much more.

author: Frankentronics
author_rank: Regular Contributor
timestamp: January 06, 2018, 11:56:28 pm
content: Quote from: RandallMcRee on January 06, 2018, 07:10:40 pmThis whole thing started with me searching the web for a schematic to build a photo preamp with my kid. The schematic I settled on uses 2SK170's. Then I searched all the component sellers I know of (DigiKey, Mouser and Jameco) and none of them had them. So, I Googled and found some on Amazon.My current knowledge of electronics is just a few of baby steps above the average person. When I saw the discrepancy on my component tester I couldn't find any answers by Googling, so I posted my question here.I can see that there are many issues that go beyond what I was expecting. So much to learn...Quote from: RandallMcRee on January 06, 2018, 07:10:40 pmJust to give me an idea of what would be involved... Would the noise parameters be measured by feeding a clear signal from a function generator (which I don't have) and comparing it to the signal that comes out?There's a reason why I ask this. One thing that I would like to learn more about is how to build audio amplifiers and amp power supplies. I know this goes beyond this post but since we touched on the subject of noise I just thought I'd ask.As always, thank you all for taking the time to answer my questions.

author: Audioguru
author_rank: Super Contributor
timestamp: January 07, 2018, 12:03:46 am
content: You want to build a "photo preamp". What is that??Do you mean A PHONOGRAPH PREAMP? Please post its schematic so we can select a modern easily available transistor for it.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 07, 2018, 12:51:29 am
content: I got my 2SK170BL from B+D Enterprises:http://www.bdent.com/2sk170bl-toshiba-audio-transistor.htmlThey are specified for the "Dorsey mod" for Shanghai FET condenser microphonesI believe that "BL" is the lowest noise version.

author: Frankentronics
author_rank: Regular Contributor
timestamp: January 07, 2018, 01:50:24 am
content: Quote from: Audioguru on January 07, 2018, 12:03:46 amWoops! That was a typo. I did in fact mean to type "phono". And here is the schematic.

author: OCT
author_rank: Newbie
timestamp: June 18, 2023, 02:05:27 pm
content: NO NO NO But if you are smart you can use them for audio preamplifier and the noise level is the same as the original The inverse capacitance is too big too this transistors are more like J107 in capacitances. just measure between the terminals of them with capacitance meter.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 18, 2023, 02:36:19 pm
content: Quote from: OCT on June 18, 2023, 02:05:27 pm

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 18, 2023, 02:41:05 pm
content: Old Thread Indeed!!!However I think the OP should be thankful he received FETS. Last time I ordered FETs from China I received NPN transistors. They were indeed falsly labeled and tested as NPN.They did work in some circuits repaired or built. Again as NPN Transistors.

author: floobydust
author_rank: Super Contributor
timestamp: June 18, 2023, 03:54:20 pm
content: What's changed in 5-1/2 years?chinese JFETs are still usually fakes or high/low bogeys re-sorted into a "good" pile. Just got some MMBFJ201's (gone due to shortages) and IDSS is on spec though.Linear Systemsoffer their LSK170(A-D, X ultra low noise) series. They've signed up for distribution with Mouser and Digi-Key. But CAD $9 ea at Digi-Key.InterFEToffers IF170, distribution with Mouser, and many other expensive boutique parts.BB/TI has newJFE150but high IDSS35mA typ. and CISS24pF too high for condenser mics, and no fTspec. You have to be careful applying it with the smoke and mirrors marketing. Also TI/BB guys participated inthread on diyAudioIs OP a noob to be welcomed or a bot? Will webcrawlers add this content to an old thread?