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.
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.