Was it a different B+ voltage when you checked those constant current loads ma max maybe? Because the cascode Mosfet M1 in them creates a Vgs level which is VDS for the JFET T1 to reach some max IDSS. At different HV across the cascode Mosfet it's Vgs changes a little.
Matching different T1 samples for the situation so they reach about same mA max could be solving the issue I mean.
I'm sorry I don't understand, what's T1s? The power transformer of PSUDII simulation?
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The PSUDII simulation only change from real is the choke 10R but used a series 220R 2W between the bridge & the choke/cap to reach the 220R choke simulation.
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I tested again without SSHV2 the CCS load and now can't reach 15mA, reach the same as with SSHV2.
If I use 2SK170 in place of J309 as used for my 26 preamp, could I reach the 15mA? If yes what Idss have I to choose?
When you first confirmed 15mA maybe it was in a hotter ambient. If you have 2SK170V >15mA they should reach. Probably some J112 or J113 can do it too. Its the JFET that produces the current in that active load CCS you are trying for. M1 IXTP D-Mosfet is just a cascode to protect the JFET from HV. You don't need to match the JFETs because you have trimmers to regulate their IDSS. But they must be able to reach beyond your target ceiling. Measure them for IDSS in few Volts VDS, as much as the VDS they see now in that circuit. Measure that across the J309s before you pull them.
That VDS is IXTP's VGS that encloses the JFET. MOSFETs can have tolerance for VGS so the difference is normal.
Test your candidate JFETs to have at least 16mA IDSS at 1.7V power supply (VDS). Making sure they will reach.
Test your candidate JFETs to have at least 16mA IDSS at 1.7V power supply (VDS). Making sure they will reach.