First step is to determine if the MOSFET you are using is external biased or internal biased and if it is internal is it fully are semi biased. The biasing will be like this:
The BF998 and BF908 are external biased devices so they need gate and source dividers. The table establishes the values needed to bias the amp
The BF904, BF909 and BF1100 are semi-biased and the biasing is less complicated.
The BF1105 and BF1109 are even less complicated since they are fully biased.
This data came from the Ap Note linked below. You can download it for more information.
Biasing Dual gate MOSFETs
Here is a diagram for a functional BF2040W amplifier. I inserted the values from the datasheet. Everything here came from the BF2040W datasheet. Maybe the background from the the BF998 Ap Note will make it easier to understand.
The pinout has one larger pin. Once you put a drop of solder on the pis it can be difficult to ID. I take a small drill and make a hole near the larger pin so I don't lose it.
ReplyDelete