Help with BF998 preamp
Thanks for the help. Well, I can see now on the spectrum analyzer that
it's oscillating. I also found that the input wasn't tuned right. I
now get around 20 dB or so
of gain but I can't seem to get rid of the oscillations. I put a slug
tuned inductor (.3uH
7-1/2 turns) on the output in place of the toroidal inductor (9t on a
T30-6) but tuning it doesn't do anything.
In this version of the Hamtronics amp, I'm using 1206 size R's and C's
and the BF998
is a SOT style package. Everything is close to the device. I tried
putting a shield made of sheet brass straddling the G1 lead, going
across the width of the board, I tried changing the R on the drain
lead and I put a SMT ferrite bead on the drain lead but it's still
taking off. I built this amp on a single sided board - could that be
my problem? Should I have built this on a double-sided board with
vias?
In the meantime, I'll try to build one on a double sided board and
drill some holes
and wire the grounds to the bottom side.
Thanks much for the help. If I get it working, I'll post some pics and
a schematic.
Curt, K8AI
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