The datasheets generally gives you the average values. The typical
values for FETs and MOSFETs are all over the map - so I won't worry that
you're not seeing the 10mA drain current. Try out your circuit, you'll
probably be happy with it.

wrote:
Hello,

I'm assembling a classic preamplifier with the BF-981 dual-gate
mosfet. The datasheet says the best noise figure is obtained with
Vg2S= 4V, Vg1S= 0V and Id=10 mA.
So I ended with a Vdd of 9V (because I had a spare 7809) and obtained
4V for Vg2 with a 68k+56k divider, Vg1= 0V through the coil of the
tuned input filter, Rs first replaced with a multiturn 500 ohm trimmer
to find the correct 10 mA point. Rs and the 56k to ground bypassed
with 10 nF ceramic.
Easy, right?
The problem is I can't get the mosfet to drain more than 7 mA (at Rs=0
ohm). I also tried to increase slightly Vg2S by replacing the 68k with
another 56k but I end with about 7.5 mA max. Bringing Vd up to 12V
makes almost no difference.
Do I have a broken BF-981 (I don't have another one handy to test) or
it could be a normal value spread for this device?

Thanks

Francesco IZ8DWF