AL-800H Instruction Manual
8
Peak Envelope Power vs. Average Power
Peak envelope power (PEP) is often misunderstood. PEP
is not
associated with the sine wave or root-mean-
square (RMS) power, and it has no fixed ratio to average power. There are
no formulas that allow accurate
conversions between average and peak voice waveform power.
PEP is the power at the crest (highest point) of the RF waveform. On SSB, the average power can vary
from a few percent of the PEP to over fifty percent of the PEP. Generally, the PEP on SSB is two to five
times greater than the average power. On CW or other constant amplitude modes (such as FM or RTTY),
the PEP is
always equal
to the average power.
Tube Life
The 3CX800A7 is a reasonably rugged tube. The anode can handle very large anode dissipation overloads
for short periods of time due to the thermal mass of the external anode. Care must be taken to avoid
exceeding the temperature ratings of the tube's ceramic-to-metal seals. The life of the tube in this amplifier
may be prolonged if adjustment periods are kept short and a brief "cool-down" periods are provided
between lengthy adjustment periods. Avoid shutting the main power off immediately after lengthy full
power CW or RTTY transmissions. After lengthy full power RTTY or CW transmissions, allow a one or
two minute "cool-down" period (without transmitting) before shutting off the ac power switch.
The most sensitive element in any indirectly heated oxide cathode tube will always be the control grid. A
fraction of a second of incorrect tuning can cause control grid damage. This is especially true in amplifiers
that use fuses or resistors to protect the grids. Fuses and resistors are much too slow and too unpredictable
to adequately protect control grids. The 3CX800A7 grids in this amplifier are protected by a fast-acting
electronic circuit. This circuit rapidly disables the amplifier when excessive grid dissipation occurs.
In the AL-800H a grid current of 150 mA (at 100 watts of drive) produces the maximum rated grid
dissipation of 4 watts per tube. This amount of grid current will also safely disable the amplifier within a
few milliseconds.
Never remove or defeat the grid protection circuit. Doing so will void all
manufacture's warranties.
WARNING:
NEVER drive this amplifier with more than 100 watts of short term average envelope power.
NEVER remove, defeat, or modify the internal electronic grid protection circuits.
Maximum power output normally occurs with a maximum of 40 to 60 mA of grid current on CW, or 25
mA indicated (50 mA peak) during a SSB two-tone test. During typical SSB voice operation, the grid
current usually moves slightly above zero. The grid dissipation is well under one watt with 50 mA of grid
current and 100 watts of drive is around on watt per tube.
The cathodes of the 3CX800A7's must reach full operating temperature before the tube is operated. The
cathodes become fully operational 180 seconds after the application of the full heater voltage. The warm-
up timer in this amplifier assures that the cathode reaches the proper operating temperature before the
amplifier can be operated. Never defeat the warm up timer or alter the heater voltage.
