MRF154 Amplifier(Motorola
Application Note AR176/AR347)
I can recommend this design to anyone seeking a reliable easy to build solid state HF + 6 metre amplifier capable of 1200 Watts output.
However it is not cheap to build due to the cost of the MOSFETS, and for watts per dollar, a tube amplifier with a pair of 3-500z can deliver more power for far less cost, and can probably take more abuse.
One of the problems with all very high power solid state amplifiers is the effective heat sinking of the active devices, and this unit has been constructed on a piece of copper bar, with the mounting surfaces for the MOSFETS milled out so that the input and output PCBs lie flat on the copper. The copper bar is then bolted to a large heatsink. Effective heatsinking for such an amplifier is a major problem in Thermal Management - you need to dissipate almost 1kW when running at 1200 Watts output.
The amplifier requires a DC supply of about 35-40 amps at 50 volts. I have found that a stabilised supply with an electronic "fuse" is very, very desirable - if an overcurrent condition is detected, the psu very rapidly shuts down and stays down until reset. The stabilised supply significantly improves IMD performance.
Note my comments on the main amplifier intro page. The 1200 Watt output is saturated power and to keep the amplifier linear, a back-off will need to be applied, which will result in a useable output of no more than 600 Watts.
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Page last updated 6/5/2001