JFETs from Linear Systems

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J

jimgross

Member
Joined 2012
Stock, or replacements for Pass F5 Turbo FE PCBs

Hi,

I've just purchased a board set for the Pass F5 Turbo from the DIYAudio store, and looking to build the V2 version amp. I'm having problems finding the correct jfets required for this project, or a suitable substitute. Is there any ETA on matched pairs at the DIYAudio store, or does anyone have any alternate sources?? Any help will be GREATLY appreciated!!!

Thanks,
Jim.
 
H

Holzarbeiter

Member
Joined 2014
Paid Member
JFETS from Linear Systems

Jason or individual in charge of DIY Audio Store,

I just talked to Paul Norton at Linear Systems and he needs you to contact him about replenishing stock of JFETS they have in stock, waiting.

Best,

P { margin-bottom: 0.08in; } Holzarbeiter


P { margin-bottom: 0.08in; }Holzarbeiter
 
G

george_ct

Member
Joined 2011
Hello. Can someone tell me which device grade A, B, C etc. is best for an Amp Camp Amplifier? It's about LSK170 which in this schematic is operated in Common-Drain mode (a buffer) that keeps the input impedance high.
Thank you in advance for your answers.
 

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A

anystereo

Member
Joined 2005
I bought some grade A quantities of LSK170 and LSJ74 JFETs a while back and have used them in my BA and F's. I am now compiling stuff to build the F6. Can someone tell me the effect on the circuit with the lower Idss. In my pre-amp I had to double the pots values, if i remember correctly. Would that be the case here too? I am also gonna try to match stuff closely and play carefully with the 2nd & 3rd harmonics, I am fascinated by this. I know there is a way to test the Jfets to determine individual Idss's can some one point me to that method? Is it possible to run balanced inputs to the F6, run separate inputs to the gates of Q3 & Q4? I have a real nice 27 tube preamp with a magnequest output B7 transformer 15k:500 CT. One possibility would be to wire the B7 directly into the circuit in place of the jensens. Would this work?
 
D

Dukja

Member
Joined 2011
Looking for some LSJ74 and LSK170 for my F5 build. It seems the Idss of 10mA is suitable. The matched pair grade B at store is currently out and seems to be very hard to get by. Store also has LSJ74 (grade D) and LSK170 (grade C).

Noob's question:
* Will the combo of LSJ74 (grade D) and LSK170 (grade C) work at all for F5? Or they have to be same Idss and maybe at least grade C?
* Any other JFET that one can buy for F5?

Thanks a lot for the help!
 
A

AndrewT

R.I.P.
Joined 2004
For best performance in an F5 style amplifier the sj74 Idss should be slightly higher than the sk170 Idss.
fitzfish's F5X Thread gives details.

There are a few N channel that can do the duty and a few more if you add a cascode.
But there are very few P channel. That's where your search should start.
 
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D

Dukja

Member
Joined 2011
Thanks a lot for the help, Andrew.

I just found out that I have 4 matched 2sk170 with 8mA Idss. And you said that sj74 should be "slightly" higher, so it seems that the 2SJ74 grade C (10-20mA) at the diyaudio store may work out for me? I'll also spend some time to learn more about it.

I also had 4 matched 2sk107 (8mA Idss), which was sent to me to work with 2sk170 in another amp kit. I have told that 2sk107 is not exactly complimentary, so I wonder which one (2sj74 with 10-20ma Idss or 2sk107 with matched Idss) will work better with my 2sk170 at hand?

Thanks!!
 
J

jfazende

Member
Joined 2017
LSK170's replace 2SK99A?

I am a newB, so please bear with me. I am restoring a Yamaha CR-3020 receiver. The main amp has a faulty dual FET (IC601-2SK99A). I have been told that a pair of LSK170's may be used to replace the 2SK99A. If that is correct, which grade would I need? A,B,C or D? I have attached a schematic of the amplifier. Any help on this matter would be greatly appreciated.
 

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A

AndrewT

R.I.P.
Joined 2004
jfazende said:
I am a newB, so please bear with me. I am restoring a Yamaha CR-3020 receiver. The main amp has a faulty dual FET (IC601-2SK99A). I have been told that a pair of LSK170's may be used to replace the 2SK99A. If that is correct, which grade would I need? A,B,C or D? I have attached a schematic of the amplifier. Any help on this matter would be greatly appreciated.
Click to expand...
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.
 
A

AndrewT

R.I.P.
Joined 2004
Dukja said:
Thanks a lot for the help, Andrew.

I just found out that I have 4 matched 2sk170 with 8mA Idss. And you said that sj74 should be "slightly" higher, so it seems that the 2SJ74 grade C (10-20mA) at the diyaudio store may work out for me? I'll also spend some time to learn more about it.

I also had 4 matched 2sk107 (8mA Idss), which was sent to me to work with 2sk170 in another amp kit. I have told that 2sk107 is not exactly complimentary, so I wonder which one (2sj74 with 10-20ma Idss or 2sk107 with matched Idss) will work better with my 2sk170 at hand?

Thanks!!
Click to expand...
slightly means look at the Euvl data and select the correct sk74 to match.
grade C is not what you require to match 8mA sk170.
 
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