Virile Boost (Fuchs Pure Gain) 2sk170

Kroars

Well-known member
Looked around a few places and can’t seem to come up with much about this circuit, in particular a good equivalent to the 2sk170. I don’t suppose the old J201 or 5457 would work (albeit different pinout)? Also heard some mentions of the J112/J113 but apparently there are various versions of the 2sk170 denoting hfe (GR/BL and another I can’t remember) do we know which version we’re looking for? Hope everyone is having a fine Sunday!
 
Some pretty good info here:

The JFET devices such as PN4091, 2SK187, 2SK363, 2SJ108, 2SK1005, 2SK1000, 2SK0615 and 2SK370 are the equivalent devices of 2SK170 JFET. Each of the devices has the same set of electrical specifications.

If you go to the URL above, the site compares 2SK170 vs J113 with results in a table:

2SK170 vs J113

In the table below we listed the electrical specifications of 2SK170 and J113 JFET devices, this comparison is really helpful for a better understanding of this device.

Characteristics2SK170J113
Gate to drain voltage (VGD)-40V35V
Gate to source cutoff voltage (VGS(OFF))-0.2 to -1.5V-0.5 to -3.0V
Gate to source voltage (VGS)-40V-35V
Gate forward current (IG)10mA 50mA
Power dissipation (PD)400mW625mW
Junction temperature (TJ)-55 to 125°C-55 to 150°C
Input capacitance (Ciss)30pF28Pf
Noise figure (NF)1 to 10dB-
PackageTO-92TO-92
 
There is no schematic, no transistor markings. It's hard to advise, because in the case of 2SK170, depending on the model, the spread of parameters is large.
 
In terms of Vgs(off) the 2sk209 (available in smd still in production) is an exact match to the 2sk170 (they both range from -0.2 to -1.5). It would be important to know the suffix on the 2sk170 in order to get a similar Idss. The pf5102 might not be a bad match either (but the pinout is different, you might have to twist the legs on the transistor)
 
I wasn't able to confirm, but I suspect this boost is based on a mu-amp (like Amz miniboost). If so, the miniboost can work with different jfets, although they might give different amounts of clean headroom. I would suggest socketing and use what you have (j201, 2n5457, etc.). If you don't like the results, then order others.
 
Looked around a few places and can’t seem to come up with much about this circuit, in particular a good equivalent to the 2sk170. I don’t suppose the old J201 or 5457 would work (albeit different pinout)? Also heard some mentions of the J112/J113 but apparently there are various versions of the 2sk170 denoting hfe (GR/BL and another I can’t remember) do we know which version we’re looking for? Hope everyone is having a fine Sunday!
LSK170 is the modern equivalent but there is A,B,C& D at Mouser
 
There is no schematic, no transistor markings. It's hard to advise, because in the case of 2SK170, depending on the model, the spread of parameters is large.
That’s pretty much what I arrived at as well. Looks like I may just get a handful of different LSK170’s and see what sounds best. Thanks!!
 
In terms of Vgs(off) the 2sk209 (available in smd still in production) is an exact match to the 2sk170 (they both range from -0.2 to -1.5). It would be important to know the suffix on the 2sk170 in order to get a similar Idss. The pf5102 might not be a bad match either (but the pinout is different, you might have to twist the legs on the transistor)
Great to know, thank you!! I do have a handful of 209’s already. They’re all smd and from the same batch, so I figure they’d be rather consistent with one another. Although, as you pointed out, it may not be the correct parameters for this circuit. At least I’ve got a few narrowed down to try; thanks, of course, to you fine folks. :)
 
LSK170 is the modern equivalent but there is A,B,C& D at Mouser
Perfect, thank you!!

Edit: holy smokes, those are not inexpensive…. Unless we can nail down a specific suffix, I think I’ll try what I have in stock. Maybe the 2sk209 as mentioned above. I’ll report back once I’ve built it. I’ve got a few others to get through first, but I’ll eventually get to it and post the results. Thanks again!
 
Q1
Vgs(off)=-0.57V at Id=4.7µA
Vgs(on)=-0.07V at Id=5.00mA
gfs=23.3mA/V at Id=3.0mA to 5.0mA
Idss=7.03mA at Vds=3.00V
Rds(on)=22.6Ω at Id=5.0mA and Vgs=0.0V

Q2
Vgs(off)=-0.55V at Id=5.0µA
Vgs(on)=-0.07V at Id=5.00mA
gfs=24.8mA/V at Id=3.0mA to 5.0mA
Idss=7.26mA at Vds=2.99V
Rds(on)=20.6Ω at Id=5.0mA and Vgs=0.0V

I'll post the schematic shortly.
 
Perfect, thank you!!

Edit: holy smokes, those are not inexpensive…. Unless we can nail down a specific suffix, I think I’ll try what I have in stock. Maybe the 2sk209 as mentioned above. I’ll report back once I’ve built it. I’ve got a few others to get through first, but I’ll eventually get to it and post the results. Thanks again!
Where do you live?
 
Where do you live?
In PA, but I’ve got TONS of components, so I should be able to find something that works. :)

Thanks for the heads up on Retroamplis! I’m always looking for more respectable/trusted shops for weirdo components. I only use Smallbear, Qwest Corp, Cabintech maybe one or two others I can’t think of right now for hard to find stuff. I’m very, very picky with new shops. Always great when one of you trusted folks offer up a hidden gem. :)
 
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