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ANADIGIT 10th November 2010 06:45 AM

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


Arnulf 10th November 2010 09:11 AM

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

ANADIGIT 10th November 2010 09:31 AM

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


Wavebourn 10th November 2010 03:52 PM

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 10th November 2010 03:55 PM

Or a simple cascode DN2540

Elvee 10th November 2010 05:11 PM

1 Attachment(s)
You can use the principles discussed here to create a 2W 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 10th November 2010 05:43 PM

the LND150 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 12th November 2010 01:03 AM

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


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