CCS with VN2222L

[ANADIGIT]

How do I use VN2222L mosfet for CCS for my 12AX7 ?
With +V supply ?

Thanks
Anadigit

 

[Arnulf]

You don't, unless you want to use your tube at extremely low Va, since it's a 60V Vds max. part.

 

[ANADIGIT]

Maybe can I use it control +VG of 12AX7 ?

Thanks
Anadigit

 

[Wavebourn]

There are 2 absolutely different kinds of VN2222LL, made by different manufacturers.
But it is difficult to find a SS device to match 12AX7: non-linear capacitors reveal themselves well on such currents.

For 6Н1П I prefer to use BSP225 MOSFETs.

 

[Brit01]

Or a simple cascode DN2540

 

[Elvee]

You can use the principles discussed here to create a 2W ccs:
http://www.diyaudio.com/forums/solid-state/173005-improved-current-source-sink.html?highlight=ccs

But with a MOS, the capacitance degrades very quickly the impedance above 1KHz (the sim uses a transistor similar to the HV VN2222, like the Supertex one. The low voltage VN2222 has less capacitance, but is limited to 60V).
And as Wavebourn said, you also have to take the non-linear effects into account.

 

[jcx]

the LND150 http://www.supertex.com/pdf/datasheets/LND150.pdf is more appropriate to the 12AX7 single digit mA plate current


a HV PNP "ring of two" feedbck ccs or Zener/LED Vref hanging from the V+ supply is a natural choice, cascode if high perfromance is necessary (PMOS pass divice also possible)


with a bufferd output stage the bootstrap RC ccs doesn't require special silicon and may be good enough

 

[ANADIGIT]

I have seen Convergent SL-1 used VN2222L and LM317 to their 12AX7 CCS, How do they do ?

With +12V supply not as other CCS which used -6.9 to -12V

Thanks
Anadigit