1kW LDMOSFET Power Amplifier 1.8-60MHz

65 Volt Version

Since August 2017 new LDMOS Transistors are available with higher operating voltage and more output power compared to the well known BLF188XR. It's the MRFX1K80 manufactured by NPX.

What are the advantages and possible disadvantages of this new transistor for HAM radio applications:

Operating Voltage 50 volts 65 volts
Drain-Source breakdown voltage 135 volts 179 volts
Gate-Source breakdown voltage -6 bis +11 volts -6 bis +12 volts
65V Output Power (Compression 1dB)  10m Band --- 1150
65V Output Power(saturated) 10m Band --- 1900
50V Output Power(Compression 1dB)  10m Band 830 825
50V Output Power(saturated) 10m Band 1270 1250
Frequency Range 1,8 bis 600 MHz 1,8 bis 400 MHz
Gain 29 dB 27,8 dB
Efficiency 75 % 75,6 %

The most important advantage of the new 65V transistor is the much higher  Drain-Source breakdown voltage. This helps designing reliable power amps a lot.

Additionally we get much more output power. The realistic output power for ham radio SW amps is between the 1dB power and the saturation power. With 50 volts we get about 1kW and with 65 volts we get almost 1,5kW. (Don't believe the Youtube videos showing 2kW, you will not want to get on the air with a signal like that and the life time of the transistor will be reduced to a few tries).

But there is also a disadvantage of the 65 volts technology: power supplies delivering 65 volts with >30A are really expensive. The well known 50V server supplies for $50 on ebay are a good solution. For a 65v supply you can easily spent 10 times of this price. Of course we can run the new transistor with only 50 volts which gives 1kW and a long life time.

Circuit design:

the PCB for the 50 Volt Version (where to buy) is fully compatible with the new 65v transistors, just a few parts have to be changed, compare with the bill of material: BOM:

C20, C21 100uF / 100V
C40, C41 470uF / 100V
R13, R24 100 ohms

that's it, change these six parts and the board is ready for the MRFX1K80 and the 65 volts supply.