Hi Ian,
Since this isn't a LTP, the matching is not critical, but you do need to be relatively close. Personally, I match the BLs to 0.1 mA, but that degree of matching may not be required, especially since you have P3, which can compensate significantly. Jim, how much difference in Idss do you allow for your JFETs in the F5?
Steve
Since this isn't a LTP, the matching is not critical, but you do need to be relatively close. Personally, I match the BLs to 0.1 mA, but that degree of matching may not be required, especially since you have P3, which can compensate significantly. Jim, how much difference in Idss do you allow for your JFETs in the F5?
Steve
0.1 is more than good enough. In the F5 the bias pots will make up for quite a bit of variation.
Thanks Steve & Jim I can see I shall have to start matching some small Jfets, I spent a whole day testing about 300 240/9240 a couple of weeks ago using a circuit I found on NP First watt site I think and was suprised how different the readings were I even went back over them to make sure nothing had changed.
Now I need to find out how close they need to be to be a "pair or quad" any thoughts lads??
Ian
Now I need to find out how close they need to be to be a "pair or quad" any thoughts lads??
Ian
Hi guys Steve, Jim etc good news I swapped out the Jefets and I've now got loads of bias adjustment I've got these sinks cooking 
The offset is perfect @ 0.001v and that's with 0.350v across the source resistors I'm going to leave it cooking for a while and see where the sinks top out temp wise they are currently are about 44c (ambient temp 19c) so looks like a good one.
Even though I have graded about 300 off 9240/240 FET's I have ordered some from buzzforb just to be safe and I've also got some JFETS on route from Spencer so looks like I might be building a family of amps ;-) once again thanks for your help and guidance.
Ian
The offset is perfect @ 0.001v and that's with 0.350v across the source resistors I'm going to leave it cooking for a while and see where the sinks top out temp wise they are currently are about 44c (ambient temp 19c) so looks like a good one.
Even though I have graded about 300 off 9240/240 FET's I have ordered some from buzzforb just to be safe and I've also got some JFETS on route from Spencer so looks like I might be building a family of amps ;-) once again thanks for your help and guidance.
Ian
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.