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-   -   Stability of 2SK170 at small currents (http://www.diyaudio.com/forums/solid-state/155452-stability-2sk170-small-currents.html)

revintage 21st November 2009 10:13 PM

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?

Rikard Nilsson 21st November 2009 10:20 PM

Lack of speed + excessive noise i would guess.

jcx 21st November 2009 10:28 PM

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

revintage 22nd November 2009 11:23 AM

1 Attachment(s)
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.

revintage 22nd November 2009 12:00 PM

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


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