Driver and final MOSFET bias adjustments
 

• Note: Before connecting the power supply turn the three multi turn bias trimmers R4, R7 and R2 so that the resistance from gates to GND of the MOSFETs TR1, TR2 and TR3 indicates minimum resistance. This ensures that the bias currents of the MOSFETs are zero in the beginning. This is important because otherwise the current can be very high and the fuse may blow.

• Connect a current meter in series with the power supply positive wire
• Cut out the RF drive from DDS board by selecting 0 Hz frequency or by disconnecting the RF input
• Key down or press PTT to activate the T/R switch
• Make a note of this stand-by current
• First adjust the final stage bias by turning the trimmers R4 and R7 until each trimmer increases the current by 25 mA
• Adjust the driver bias by turning the trimmer R2 until the current increases 100 mA
• The final current should be the stand-by current + 150 mA

• If you don't need the built-in SWR bridge you can omit the assembly of the switch SW1 and the three 150 ohm mini-melf resistors R8, R9 and R10. Then it is neede to solder a jumper wire instead of R8