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Old November 8th 07, 11:28 PM posted to rec.radio.amateur.homebrew
nx7u nx7u is offline
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First recorded activity by RadioBanter: Oct 2006
Posts: 13
Default BF981 classic preamp

Tom et. al.,
You're right...I misread the datasheet, it shows Id skyrocketing if
Vg1s0. But of course the protection diodes should do the trick. The
datasheet also specifies Vg1s and Vg2s breakdown at 6V. So although
for practical purposes the gates are not interchangeable, it shouldn't
have killed the part.



On Nov 7, 10:18 pm, K7ITM wrote:
On Nov 6, 5:20 pm, nx7u wrote:
...

3. No the gates are not interchangable.


That's generally true of dual-gate mosfets, of course. Gate 2 is
similar to the control element of the upper transistor in a cascode.
Thus, in typical operation, gate 2 has very little effect on drain
current.

4. The datasheet does not give any Vg2s/Id curves, and Vg1s cannot be
positive (max gate current is exceeded nearly immediately) so you're
stuck with 7mA for this part.



TOm