But it was recommend to use J74`s with Idss of 8mA.
Dont know why but i believe it.
So if i get LSK Dual Jfet with 3mA is way to less and 10ma and more is way to much.
But this is only interesting to stock me some reserves.
Or make for fun a preamp with smd parts.
At the moment i dont Need any jfets or maybe...
For the non-acronym savvy, I take it that by CCS, you mean "Constant Current Source", aka Simple transistor current sources, as discussed at:
Current source - Wikipedia
nope
you need complementary pair (matched , of course) in BL range - to keep dissipation on bay
you could use pair of V ones , after measuring their exact Ids , then deciding where (voltage wise) to cascode them .... exactly from same reasons
trivial in fact , but demands some play with any pcbs you have
..... still trivial - all you need is dremel , 0.7mm drill and some fine wire
you need complementary pair (matched , of course) in BL range - to keep dissipation on bay
you could use pair of V ones , after measuring their exact Ids , then deciding where (voltage wise) to cascode them .... exactly from same reasons
trivial in fact , but demands some play with any pcbs you have
..... still trivial - all you need is dremel , 0.7mm drill and some fine wire
V Grade max Idss is 20mA.
If you cascode at 9V Vds, dissipation is 180mW.
Those devices are rated at 400mW for 125°C junction temperature.
Which means at 180mW the junction temperature is about 70°C, which is OK.
Of course additional heat sinking will always help.
Cheers,
Patrick
If you cascode at 9V Vds, dissipation is 180mW.
Those devices are rated at 400mW for 125°C junction temperature.
Which means at 180mW the junction temperature is about 70°C, which is OK.
Of course additional heat sinking will always help.
Cheers,
Patrick
B&D enterprises is selling Toshiba 2SJ74/2SK170 pairs which are NOT matched. I gambled $100 and bought 10 pairs. Here's the Idss range I got:
SJ74: 10.0,10.0,9.9,9.3,8.7,8.6,8.2,7.5,7.3,6.7
SK170 10.1,10.0,10.0,10.0,10.0,9.8,9.5,9.2,9.0,8.9
SJ74: 10.0,10.0,9.9,9.3,8.7,8.6,8.2,7.5,7.3,6.7
SK170 10.1,10.0,10.0,10.0,10.0,9.8,9.5,9.2,9.0,8.9
That's pretty good. A few matched 74/170 pairs and also some reasonably matched 170 pairs. Your gamble paid off. 
Yeah not bad considering current pricing. If you look closely there could be a couple reasonably close 74/74 pairs left over. Aleph J anyone?
Hey Kevin,
The jfet values look fine. However, this is both good and bad news.
The good news is you have at least enough for 2 amps.
The bad news is you may find yourself going to "Amplifier Anonymous" meetings
in the future. 🙂
But until then, do consider the Aleph-J.
Dennis
The jfet values look fine. However, this is both good and bad news.
The good news is you have at least enough for 2 amps.
The bad news is you may find yourself going to "Amplifier Anonymous" meetings
in the future. 🙂
But until then, do consider the Aleph-J.
Dennis
I use conventional speakers that drop down to 3ohm in the mid bass so I think the Aleph J is not for me. Anyway the 74/74 pairs have already moved on to another member who is building the Aleph J.
