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Old 10th November 2010, 06:45 AM   #1
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Default CCS with VN2222L

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

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Old 10th November 2010, 09:11 AM   #2
Arnulf is offline Arnulf  Europe
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You don't, unless you want to use your tube at extremely low Va, since it's a 60V Vds max. part.
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Old 10th November 2010, 09:31 AM   #3
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Maybe can I use it control +VG of 12AX7 ?

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Old 10th November 2010, 03:52 PM   #4
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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.
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Old 10th November 2010, 03:55 PM   #5
Brit01 is offline Brit01  United Kingdom
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Or a simple cascode DN2540
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Old 10th November 2010, 05:11 PM   #6
Elvee is offline Elvee  Belgium
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You can use the principles discussed here to create a 2W ccs:
Improved current source/sink

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.
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Old 10th November 2010, 05:43 PM   #7
jcx is offline jcx  United States
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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
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Old 12th November 2010, 01:03 AM   #8
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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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