600 Watt HF Amplifier

  Amplifier Description

  • There's an old axiom in amateur radio which states "Life's too short for QRP." While I generally disagree, it certainly appears to be true for 75m AM operation here in central North America, where a one watt carrier can quickly become buried in QRN & QRM. This amplifier is a mate for the QRP 75m AM Transceiver described elsewhere at this site.
  • The amplifier uses four Motorola MRF150 50 volt TMOS power FETs configured in push - pull/parallel and biased for class AB linear operation. This scheme yields a power gain of 20db. The 1 watt drive from the "Wheat Box" will produce a 100 watt carrier (400 watts PEP @100% modulation) with headroom to spare.
  • There's little original design here. The basic 2 ⇒ 30MHz PA brick is straight from Motorola's application note EB104. The power supply, low-pass output filter, control circuitry and instrumentation are mine. Still, I would describe this project as mostly an exercise in packaging.

  Some Amplifier Highlights

  •  Mode of operation − Class AB linear
  •   Output power − 600 watts PEP into 50Ω load
  •   Maximum drive power − 6 watts PEP into 50Ω input impedance
  •   Undesired output energy − at least −50dbc
  •   Power Source − 120v 60∿ nominal
  •   Front panel controls
    •   AC Power
    •   Mode Switch
      •   Standby
      •   20 DB − full output
      •   14 DB − Via a 6db pad at brick input to produce 100 watts PEP for driving a legal limit amplifier
  •   Illuminated metering, left to right:
    •   PA current − 15A full scale
    •   Relative RF output
  •   Rear panel connections
    • SO239 RF input connector
    • SO239 RF output connector
    • BNC connector − sample of RF output to monitor oscilloscope
    • RCA connector for T/R control input signal
    • AC Line cord
    • Fuse access (10A SB)
  •   Physical
    •   Size − 16¾"W x  8¾"Hx 12¼"D
    •   Weight − 43 lbs.

eb104  The EB104 Circuit Board

      

  Data Sheets

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