Communication Concepts EB63A Construction Hints - Manual (Page 4)

Install the 330pF mica capacitors, C8 and C9, on top of the PC board as shown. The
capacitors should stand approximately ¼” above the PC board.
This now completes the assembly of the amplifier. The unit may now be tested.
1. Hook up a power supply of suitable current output to the amplifier. A regulated
power supply capable of delivering 13.65 volts DC at 25 amps minimum is
recommended for this amplifier operation.
2. Connect the output through a power meter to a suitable 50 ohm dummy load of a
rating capable of handling the power output (200 watts minimum). Use 50 ohm coax
cable.
3. “Slowly” bring up or increase the input power until the output equals the maximum
power recommended in the Engineering Bulletin.
4. The output of the amplifier contains harmonics of the input signal. Thus if direct
operation into an antenna is expected, filtering of the output is necessary to meet
FCC regulations for spectral purity. The low pass filters shown in Figure 1 will
provide more that sufficient harmonic attenuation with less than 1 dB of loss at the
operation frequency.
TROUBLESHOOTING
Caution!!!…. Never operate the amplifier, even without a RF input signal, without the RF
transistors being mounted on a proper heatsink. The RF transistors can heat up and
destroy themselves almost instantly if the are not heatsinked properly.
The input RF signal level should be between 1 and 5 watts. The amplifier will handle up
to 6 or 8 watts safely. However, 25 watts from some of the transceivers will destroy the
RF transistors very quickly. So beware of that power level switch position on those
transceivers which are capable of putting out 25 watts.
As with most HF amplifiers without frequency compensation networks, it takes much less
power at the low end of the frequency range (2 MHz) to drive the amplifier to full output.
Typically 2 to 3 watts will drive the amplifier to 140 watts at 2 MHz. At the high end
(28MHz) it takes upwards of 7 to 8 watts to obtain the full 140 watts output. Just be
careful not to exceed the ratings of the transistors. Operating the amplifier at an
excessive power output level will shorten the life of the RF transistors.
Be sure that an adequate size heatsink is used. The heatsink has to dissipate 140 watts
of power. If heavy-duty usage of the amplifier is anticipated, it is recommended that a
fan also be used to blow air over the fins of the heatsink and over the amplifier board
itself.
TYPICAL PROBLEMS ENCOUNTERED
1. Relay chattering or relay will not hold in – check the power supply voltage. If a
battery is used and the voltage drops to 11 volts and below when RF is applied, the
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