Question about FET 2SK117 in old stereo receiver

[EUVL]

Zeljko,

The schematics you posted showed the 2SK117s being using as a diff pair at the inputwith no source degeneration. They are driven by a current source with about 8mA constant current ((12V-0.6V)/150R).

This determines what you need for the 2SK117s, namely, they should be matched devices with Idss of about 8mA (I would not go much lower than 6mA even if you assume you never get full swing on the diff pair due to negative feedback). That means GR or (better still) BL. They will see half of that, i.e. about 4mA, with no input signal.

2SK117Y has a max Idss of 3mA, which means that you will forward bias them even with no signal. I would advise you against that but others seem to have another opinion, though I have yet to hear their arguments.

If you have difficulties getting 2SK117BL (though they seems to be quite available), you can replace them with 2SK170BLs without too much difficulty. The capacitances are higher by a factor of 2, but transconductances is also 50% higher.

Failing all that, send me a private email. I can probably help you, but only for once, with 2 matched pairs 2SK117BLs.


Patrick

[Zeljko]

Originally posted by EUVL
Zeljko,

The schematics you posted showed the 2SK117....

That is very good explanation!! Thank you!!

Originally posted by EUVL
2SK117Y has a max Idss of 3mA, which means that you will forward bias them even with no signal. I would advise you against that but others seem to have another opinion, though I have yet to hear their arguments.

That I am looking for, thank you so much!

Originally posted by EUVL
If you have difficulties getting 2SK117BL (though they seems to be quite available), you can replace them with 2SK170BLs without too much difficulty. The capacitances are higher by a factor of 2, but transconductances is also 50% higher.

OK you probably mean here replace with 2SK117GR without too much difficulty. I can buy on some other way 2SK117GR.

Originally posted by EUVL
Failing all that, send me a private email. I can probably help you, but only for once, with 2 matched pairs 2SK117BLs.

Thank you for an offer, its very kind from you, but I will buy some GRs. How you can find matched pairs of 2SK117?

Regards!

[Zen Mod]

Originally posted by EUVL
Zeljko,

The schematics you posted showed the 2SK117s being using as a diff pair at the inputwith no source degeneration. They are driven by a current source with about 8mA constant current ((12V-0.6V)/150R).

This determines what you need for the 2SK117s, namely, they should be matched devices with Idss of about 8mA (I would not go much lower than 6mA even if you assume you never get full swing on the diff pair due to negative feedback). That means GR or (better still) BL. They will see half of that, i.e. about 4mA, with no input signal.

2SK117Y has a max Idss of 3mA, which means that you will forward bias them even with no signal. I would advise you against that but others seem to have another opinion, though I have yet to hear their arguments.

If you have difficulties getting 2SK117BL (though they seems to be quite available), you can replace them with 2SK170BLs without too much difficulty. The capacitances are higher by a factor of 2, but transconductances is also 50% higher.

Failing all that, send me a private email. I can probably help you, but only for once, with 2 matched pairs 2SK117BLs.


Patrick

Patrick..............

ECA VRT sez for that VD1212 diode :

"1,24..1,34V(1,5mA) "


so CCS seems that have smaller current...........

[Zen Mod]

Originally posted by Zen Mod



Patrick..............

ECA VRT sez for that VD1212 diode :

"1,24..1,34V(1,5mA) "


so CCS seems that have smaller current...........

hehe
and not 76mA ,fer sure.........

[EUVL]

> ECA VRT sez for that VD1212 diode :
> "1,24..1,34V(1,5mA) "

My mistake (too lazy in the morning to check datasheet).
I take back what I said and apologise to all, especially to Zeljko.

If 1.34V, then CCS has current = (1.34-0.6)/150 = 5mA

Each FET (2SK117) will have bias at 2.5mA, and 5mA max.
In that case I would still use GR with Idss >= 5mA.

(One can argue that one can use Y with Idss 3mA and let the JFET goes into slight positive bias. For me it is bad practice, plus that the chances of getting max. Idss as in spec are, from experience, not great. So the recommendation for GR or BL stands.)

> How you can find matched pairs of 2SK117?

Buy 100 pcs and match myself.

2SK117 is the JFET of choice by Japanese DIYers (promoted by Kaneda) because they have the lowest capacitance / transconductance.


Patrick

[Zeljko]

OK, I learned so much about those FETs in this therad, thank you guys, especially to Zen Mod and Patrick!
But now, I have one big problem, when I have found 2SK117Y in my local store, I was so happy that I bought 50 pieces of them ! So do you maybe know someone who need those 2SK117Y to buy or to change them with GR or GL type?

Regards!

[Zen Mod]

Originally posted by Zeljko
OK, I learned so much about those FETs in this therad, thank you guys, especially to Zen Mod and Patrick!
But now, I have one big problem, when I have found 2SK117Y in my local store, I was so happy that I bought 50 pieces of them ! So do you maybe know someone who need those 2SK117Y to buy or to change them with GR or GL type?

Regards!

can you change them for anything else (BL marked) in same shop?

[Zeljko]

Originally posted by Zen Mod



can you change them for anything else (BL marked) in same shop?

No, they have only with mark Y

Zeljko

[Zen Mod]

Originally posted by Zeljko


No, they have only with mark Y

Zeljko

just put these Ys in place and try it