FWIW, I found the following SPICE model for the BF998 on the web -- note
that the two MOSFETs VMAX are dissimilar, a lot of the entries are for
parasitic elements:

* BF998 SPICE MODEL OCTOBER 1993 PHILIPS SEMICONDUCTORS
* ENVELOPE SOT143
* 1.: SOURCE; 2.: DRAIN; 3.: GATE 2; 4.: GATE 1;
..SUBCKT BF998 1 2 3 4
L10 1 10 0.12N
L20 2 20 0.12N
L30 3 30 0.12N
L40 4 40 0.12N
L11 10 11 1.20N
L21 20 21 1.20N
L31 30 31 1.20N
L41 40 41 1.20N
C13 10 30 0.085P
C14 10 40 0.085P
C21 10 20 0.017P
C23 20 30 0.085P
C24 20 40 0.005P
D11 42 11 ZENER
D12 42 41 ZENER
D21 32 11 ZENER
D22 32 31 ZENER
RS 10 12 100
MOS1 61 41 11 12 GATE1 L=1.1E-6 W=1150E-6
MOS2 21 31 61 12 GATE2 L=2.0E-6 W=1150E-6


..MODEL ZENER D BV=10 CJO=1.2E-12 RS=10


..MODEL GATE1
+ NMOS LEVEL=3 UO=600 VTO=-0.250 NFS=300E9 TOX=42E-9
+ NSUB=3E15 VMAX=140E3 RS=2.0 RD=2.0 XJ=200E-9 THETA=0.11
+ ETA=0.06 KAPPA=2 LD=0.1E-6
+ CGSO=0.3E-9 CGDO=0.3E-9 CBD=0.5E-12 CBS=0.5E-12


..MODEL GATE2
+ NMOS LEVEL=3 UO=600 VTO=-0.250 NFS=300E9 TOX=42E-9
+ NSUB=3E15 VMAX=100E3 RS=2.0 RD=2.0 XJ=200E-9 THETA=0.11
+ ETA=0.06 KAPPA=2 LD=0.1E-6
+ CGSO=0.3E-9 CGDO=0.3E-9 CBD=0.5E-12 CBS=0.5E-12


..ENDS BF998

Ah, but that's a model for just one BF998. The one you pull out of the
drawer might bear very little resemblance to it.

Roy Lewallen, W7EL

jack wrote:
FWIW, I found the following SPICE model for the BF998 on the web -- note
that the two MOSFETs VMAX are dissimilar, a lot of the entries are for
parasitic elements:
. . .

Doesn't say much about their quality control if the devices are that
dissimilar.

FWIW, I have developed a semiconductor and tube curve tracer for use within
Multisim -- create the component in Multisim, plug it into the curve tracer,
run the test and compare with the manufacturer's charts.

I have also built a tube curve tracer -- same will apply for
semiconductors -- even published an article on it. With this i can compare
the characteristics of the device vis a vis mfr data sheet AND the
simulation in EWB.

Jack

"Roy Lewallen" wrote in message
...
Ah, but that's a model for just one BF998. The one you pull out of the
drawer might bear very little resemblance to it.

Roy Lewallen, W7EL

jack wrote:
FWIW, I found the following SPICE model for the BF998 on the web -- note
that the two MOSFETs VMAX are dissimilar, a lot of the entries are for
parasitic elements:
. . .