Amplifiers


1296MHz Power Amplifier

This is a home made 60W output hybrid coupled amplifier for 23cm.  The first photo shows one of the two amplifiers comprising the 60W assembly.  The second photo shows the completed 60W assembly with heat sinks and output power combiner.

432MHz Power Amplifier

This is a 200W solid state 432MHz power amplifier.  This home made amplifier is located approximately 500' from the operating position.  It is a 2 stage Kurokawa coupled amplifier, driven by a home made transverter that functions in conjunction with the Kenwood TS-930S.  

144MHz Power Amplifier and Preamplifier

The image on the left shows the 2 meter power amplifier/preamplifier that resides at the base of the Big Bertha tower (see Antenna Farm).  In the foreground, from left to right, is the output TR relay, the output filter and diplexer, a 3 resonator helical band pass filter, a simultaneous gain and noise matched preamplifier (blue box), and finally, the input TR relay.  The large heat sink assembly in the rear is the 500W output solid state power amplifier.  All of the amplifiers and filters in this assembly are home designed and fabricated.

This is a detailed view of the inside of the 500W power amplifier.  This amplifier uses a pair of Motorola MRF151G transistors.  On 2 meters, this transistor is the solid state equivalent of the venerable Eimac 4CX250B.  The transistors dissipate 300W each in approximately 1/2 square inch of area.  This necessitates them being mounted to a 1/4" thick solid copper plate, which spreads the heat from the transistors to the aluminum heat sink below.  The outputs of the two stages are combined using branch line couplers fabricated from coax, which can be seen on both the left and right sides of the amplifier.  The amplifier operates on 48VDC, and has an intermodulation distortion of -33dB PEP at full output.

This is a diplexing filter which passes the 144MHz signal to the antenna.  At the same time, the harmonics generated by the amplifier are harmlessly diverted to a 50 ohm load.  This filter improves the intermodulation performance of the amplifier, along with its stability and permits simultaneous operation on 2 meters and 70cm without overload on the 70cm band.

6 Meter Power Amplifier

This 8877-based amplifier was designed and built by WA7TZY.  It features a pi-L output network without a plate tuning capacitor.  Plate tuning is accomplished by means of a variable inductor (squeezy coil) as seen in the picture below left.  The input capacitance of the pi network is provided by the plate to grid capacitance of the 8877 tube.  Note also that the plate voltage is applied at the 250 ohm impedance point of the pi-L rather than at the traditional high impedance point.  The input is also a pi network, where the cathode grid capacitance forms part of the pi network.  The input and output networks were modeled on a computer using MicroSmith by W7ZOI.  Appropriate resistances were temporarily inserted for the cathode and plate load impedances.  The input and output networks were tuned with the aid of a network analyzer.  Voltages and drive are applied to the amplifier, and the amplifier delivers full power without additional adjustment.  A quarter wave stub on the output of the amplifier provides protection in the event of failure of the blocking capacitor.

The second picture shows a front panel view of the completed amplifier.