JFETs from Linear Systems

[jfazende]

I have not been able to find a 2SK99 data sheet. That has been one of my problems finding a replacement.

 

[jfazende]

Looks like the FETs are operating @ ~ 1.7mA each.
An Idss > 3mA maybe 4mA to 5mA would do.
Check the sk99 datasheet and see what the gm is at that 1.7mA Id
Then look for a device that has similar gm at the same current.

I have not been able to find a 2SK99 data sheet, so I don't know what the gm is.

 

[jfazende]

AndrewT - I'm really struggling to find an equivalent to the 2SK99A. A member of different forum gave the following K99A specs:
VGSS -25V
IG 10mA
PD 100mW x2
IDss 1.5ma to 20ma
gm 80mOhm min (VDS=10V f-1kHz) that's a problem, usually such double FET in same package gives a MIN of 15mOhm not 80...

 

[labjr]

Are there any equivalent JFETs in an SMD package? I'm wondering what would a manufacturer use if they didn't already have a stockpile?

 

[jfazende]

The 2SK99A is used the the first stage of the power amp in a vintage Yamaha CR-3020 receiver. Already contacted Yamaha, they didn't have any stockpiled parts or equivalents. Their only suggestion was to search online forums such as this one and eBay. :-(

 

[AndrewT]

I don't follow his spec.
Vgss is not given by Onsemi, Linear and Toshiba
Vgss(off) is used by Fairchild
gm = 80milli-mhos (mS) is exceptionally high. I think that is a mistake.
Based on those two parts of his spec, I'm inclined to not use any of it.

 

[jfazende]

I have tried matched pairs of 2SK170BL's from two different supposidly reliable sources with no luck. I have received some LSK170's Grade B from DIYAudio store. Haven't tried them yet, not sure Grade B is what I need.

 

[r_jik45]

Hi,
I got lost with the specs and might have missed the info...
What is the recommended grade of LSK170 for the "Mezmerize B1 Buffer"?
Thanks!

 

[r_jik45]

Ok.... B grade according to one of Salas' posts

 

[syracuze]

Asking help from collective wisdom of diyaudio community

Bringing together parts for my F5 build; as the diyaudio store is stock out for the matched JFET LSK170/LSJ74 pairs, I happened to order the pack/8 piece versions but all in A grade, learnt only after that I needed to get B grades.
Would it be possible to build an F5 with A grade Jfets? If yes what would be the compromise vs. the B grades?
Many thanks

 

[Olaf S]

Hi, good morning from Germany.
My question, i would build a F5 TV3 with 8 transistors per rail.
Mr Pass wrote in the manual, in this case we must double the SJ74/Sk170 for stable operation.
Can i use one c oder d grade for this, or must i use a pair of B?

Kind regards
Olaf

 

[mbedwani]

Wooo Hooo - DIYAudioStore has matched B's in stock

 

[Jason]

They are indeed now back in stock. There is a limit of 1 per customer per month in order to keep these in the hands of DIYers who are making projects, so they all get used. If you need more than that for a special purpose, please email contact@diyaudistore.com.

 

[astromo]

LSJ74 Resupply Forecast

Any forecast on the resupply of the LSJ74 matched pairs?
J74/J74 Stereo Differential Kit


I registered for notification but I think it's been more than a month now.


Any news, regardless of the answer, would be appreciated.


Cheers

 

[Jason]

Any forecast on the resupply of the LSJ74 matched pairs?
J74/J74 Stereo Differential Kit


I registered for notification but I think it's been more than a month now.


Any news, regardless of the answer, would be appreciated.


Cheers

We are told "2-3 months", but that's been the case for a long time now. We're hopeful!

 

[labjr]

We are told "2-3 months", but that's been the case for a long time now. We're hopeful!

I wonder they still seem to be unable to produce significant quantities of those parts in a timely manner?

 

[Jason]

I wonder they still seem to be unable to produce significant quantities of those parts in a timely manner?

Without going into too much detail: The amount of available parts = (production cycle duration * yield of parts from the fabrication process that meet all specifications, for each grade) - demand for each grade.

Speeding up the cycle, refining the fab process to create more yield of the spec most in demand, would resolve the situation, and I hear they are working on both angles.

 

[hillextor]

Hi Jason,
Do you know when the LSJ74B could be back in stock, I need 4 marched pairs of LSK170B/LSJ74 to replace the Toshiba part on an up amp

 

[Jason]

There's matched NP pairs on their way, but our supplier currently has not given me an ETA for when they will ship. Hopefully they'll be available to purchase within the month.

 

[astromo]

There's matched NP pairs on their way, but our supplier currently has not given me an ETA for when they will ship. Hopefully they'll be available to purchase within the month.

Encouraging news. If NPs are on the horizon, what's the outlook for PPs to suit Aleph builds?

O Maybe split a few NPs and divert the N-JFETs to the ACA pile. Just putting it out there.