Stability of 2SK170 at small currents
 

Normally we run the 2SK170 well over 5mA when used as gainstages.

Intend to use a 2SK170 as a simple CCS at 0,1mA and ca 30V over it. Will there be any drawbacks at the low currents I mentioned?

Lack of speed + excessive noise i would guess.

large parasitic C with the large die makes for a very poor ccs at higher frequencies

Seems like those drawbacks doesn´t show up in this application, checked with a resistive network instead and no noticeable change.

The third 2SK170 is used as a CCS with 470k to ground. The CCS sets the output voltage through the gyrator whose gate has to be fed high-ohmic to function.

This one will output 30Vrms(B+=75V) into 10kohm with indications of well below 0.1% THD at a Zout of ca 500ohm.

Small error: 30V peak (60V ptp) not 30Vrms. But 25Vrms at below 0,1%.