5W PA Bias

Vernon Matheson

I finished up the 5w pa and put it in line this morning.


I was going to adjust the bias on the PA by just increasing the R1 trimmer until the output stops and then knock it back a tad.


The problem is that I increase the trimmer but the output doesn’t stop increasing. It goes to 10 watts on the Oakhill meter and wants to keep going J


On 40 and 80 meters with the trimmer fully anticlockwise I am still showing 5 watts output and the heat sink is warm.


I tried adjusting the bias on 10m where the output should be the lowest but it just ramps way up.


I put the amp together using the simple construction…no cosine shaping etc.


I am supplying the amp with 12 volts.


I will check my watt meter for calibration just to be sure.


Should I drop the supply voltage to the amp or have I done something wrong here?



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