Replacement For Toshiba 2SK170/2SJ74

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#47
amy P complement to BF862?

maybe degenerating a bit the BF862, is there any complement to build input buffer à la F4
or BAF2013 LSK preamp?



861A could complement J270
861B with J271
861B with j309
861C with J310

???
 
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#51
marconi118 said:
... Could someone evaluate if my proposed alternative pairs could match? I am too new to that stuff to successfully compare datasheets
Click to expand...
None of them is a good match for a beginner unless the goal is merely to build a circuit that can produce "some sort of sound" of questionable quality. You have to understand the behavior oh the jfets in circuit, match, tweak, measure and assure stability to successfully use them. Once you understand and equipped adequately, you will no longer ask these kind of questions.
 
#52
They have been many many threads that has dealt with the same discussion.

There is simply NO 1:1 replacement for 2SK170/2SJ74 complementary pair.
The only that came close was 2SK163/2SJ44, with lower Yfs.
But they were long obsolete before 2SK170/2SJ74.

2SK246/2SJ103, which are now also obsolete but perhaps easier to find, are NOT direct replacement.
They have much lower Yfs and much higher noise.
In certain circuits, e.g. a JC-2, they can be used as substitutes with penalties in both distortion and noise.
But this applies only in certain cases, e.g. when the circuit itself uses a lot of open loop gain and hence negative feedback.

For single ended applications, such as a LTP or source follower with matched 2SK170, one can still consider :
2SK117, 2SK209, BF862, 2SK3557-6, ..... etc.
But they are not 1:1 replacements also.
2SK117 / 2SK209 have lower Yfs. BF862 has higher leakage current, ....
And even these are disappearing very quickly.

So the best solution is still just to accept the cost and buy matched pairs from the few reliable sources named here.


Patrick
 
#55
Jim, I think Scott is also referring to the low noise LSK189/LSJ289 and LSK489/LSJ689 combo. Nice higher yield parts with ~330 ohm output impedance when used in complementary follower style circuit. Very usable in many applications.
 
#56
I should correct myself first.
I should have mentioned LSK170/LSJ74 as replacement equivalents by Linear Systems.

> I don't know what could be wrong with LSK170's as followers?

Nothing.

But for the price one has to pay for the LSK170, one can easily (still) get original Toshiba, matched.
Linear Systems LSK170 Ultra Low Noise Single N-Channel JFET (8 Pieces) – diyAudio Store
Toshiba 2SK170 FOUR MATCHED PAIRS (4 pairs) to 0.03mA / 4mV in Temp Control Lab | eBay

(2nd link was from Nelson in post#20.)

> The LSK/J parts are wonderful.

But also according to you in post #6 :
"Linear Systems is trying to make the J74s but their yields are very low."

Low yield means high prices :
Linear Systems LSJ74 Ultra Low Noise Single P-Channel JFET (8 Pieces) – diyAudio Store
Toshiba 2SJ74 MATCHED QUAD to 0.03mA / 4mV 6.5mA - 7.9mA Idss Range | eBay

And if I understand correctly, those (8 pieces sets) from the store are unmatched.
So one has to add a premium for matching for 1:1 comparison.

And according to measurement by Dimitri (also ours), LSK170 has higher noise level, at least for some examples :
http://www.electronicdesign.com/sites/electronicdesign.com/files/uploads/2013/04/IFD2542_FO.jpg


Patrick
 
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#57
> low noise LSK189/LSJ289 and LSK489/LSJ689 combo with ~330 ohm output impedance

That compares to ~ 15ohm for a 2SK170/2SJ74 pair.
And I already mentioned that you can change the circuit to suit.
But a high Yfs part will always have better performance.
So for me not worth the asking price, at least not as they stand now.

I know I am biased.
I don't have to declare "America first".

😉


Cheers,
Patrick
 
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