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Simple 400 Watt
RF Amp for
80 meters

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The Two Module, 300 to 500 Watt RF Amplifier for 160 and 80 Meters

This Class E RF amplifier will deliver between 300 and 500 watts of RF, depending on the input voltage and tuning parameters (current). The amplifier uses two DEIC420 Driver ICs (one per module), and is easily band switched between 160 and 75 meters using relays. Transient Voltage Supressors (TVS devices) are used on the gate bus, drain bus and modulated DC input to the RF amplifier to protect the MOSFETs from damage due to accidental overvoltage. The carrier DC voltage should be between 40 volts and 50 volts, and no more than 130 volts at full positive peak modulation.

Here is the schematic in PDF format

Construction Notes: The shunt capacitors C7, C8 and C9 along with C11, C12 and C14 do not have to be individual capacitors. You could use a single 2000pF capacitor of a sufficient current rating (6 amperes or more is recommended). The design called for 2000pF of capacitance, and these were the values I had on hand at the time. Two 1000pF capacitors would work just as well as the two 500pF and single 1000pF shown in the circuit. The reason at least two capacitors should be used is to get a higher current rating, and to distribute the RF current between multiple devices. Otherwise, the shunt capacitor is simple multiple capacitors in parallel.

This 10 MOSFET RF amplifier consists of two identical 5 MOSFET RF amplifier stages connected together in a single ended push pull configuration. Each amplifier stage (module) is driven by a single DEIC420 Drive IC. The driver ICs take a standard TTL (5V) input, and each IC is driven out of phase with the other, so when one is "on" the other is "off". The outputs are also combined out of phase, giving the single ended, push pull configuration. TVS (TransZorb) devices are used on the drain and gate busses, and on the modulated DC input to each amplifier stage.


Driver

The transmitter uses the DEIC420 driver IC, one for each module. Each driver IC has its own LM2576 +12V switching regulator. The LM2576 can deliver up to 3 amperes of DC at 12V - more than enough current for the DCIC420 on 75 and 160 meters. The output terminal (a wide, flat silver plated lead) of each of the driver ICs should be directly soldered to the gate bus of the respective module, at the center. The ground terminals of each driver IC are connected directly to the source bus, and two bypass capacitors are used on the +12V DC input for each IC. The TTL input to the drivers is delivered via 50 ohm coax cable (RG58 or similar 50 ohm thin cable), and each cable is terminated by a 100 ohm resistor to ground and a 100 ohm resistor to a bypassed (at the IC) +5V source. The gate waveform produced by the DEIC420 driver is
very good on 75 meters, and approaches
a true square wave on 160 meters. This results
in a very stable and efficient class E amplifier. - - -

Band Switching

Relays RY1 and RY2 are used for bandswitching between 160 meters and 75 meters. When using the RF amplifier on the 75 meter band, relay RY1 is activated, shorting out the 160 meter coil. Relay RY2 is open, removing the extra shunt capacitance needed for 160 meters from the circuit. On 160 meters, relay RY1 is opened, putting the 160 meter tank coil in series with the 75 meter tank. Relay RY2 is energized, adding another 1200pF of shunt capacitance to each RF amplifier, as required for 160 meter operation. The frequency of the RF voltage fed to the Schmidt trigger / phase splitter must also be switched to the appropriate band.