AMERITRON AL-80B, Инструкция по эксплуатации

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AL-80B Instruction Manual
8
Tube Life
The 3-500Z is a reasonably rugged tube. The primary concern in this tube are element failures from
excessive temperatures. Element temperature is a function of the duration and the amount of power
dissipated. The elements in the 3-500Z have very good immunity to short term overload failures.
The anode in the 3-500Z can tolerate large dissipation overloads for short periods of time due to the
thermal mass of the anode. Anode color is a good indication of correct tube operation. The anode
in the 3-500Z is designed to operate at very high temperatures. These temperatures normally
produce a dull to bright red anode color. This is a normal operating condition.
The anode is coated with a "getter" material that de-gasses the tube. This material is activated by
the high anode temperatures. The likelihood of a long term gas failure is reduced by operating the
3-500Z with a slight amount of anode color.
Care must be taken to avoid exceeding the temperature ratings of the tube's glass-to-metal seals.
The life of the tubes in this amplifier may be prolonged if tuning periods are kept short and a brief
"cool-down" periods are provided between tuning periods. Try to allow a one or two minute non-
transmitting "cool-down" period after lengthy CW or RTTY transmissions before shutting off the ac
power switch.
Incorrect operation is most likely to damage the tube's control grid or anode. Applying full drive
power for several seconds with excessively "light" loading can cause control grid damage. Several
seconds of high drive power operation with improper tuning or excessively "heavy" loading can
melt or damage the anode. These conditions can be avoided by following the tuning procedures in
this manual.
In the AL-80B, a grid current of 250 mA (at 100 watts of drive) produces the rated grid dissipation
of 20 watts. For maximum tube life, the grid current and drive power should always be kept below
these values.
WARNING:
NEVER drive this amplifier with more than 100 watts of short term average envelope power.
NEVER allow the grid current to exceed 250 mA under any operating condition.
Maximum power output normally will occur with approximately 175 mA of grid current on CW, or
approximately 45 mA of maximum grid current (175 mA instantaneous peak) on SSB (two-tone
test). The grid dissipation with 175 mA of grid current and 70 watts of drive is approximately ten
watts.
If you wish to add control grid protection to the AL-80B, always remember fuses and resistors are
too slow and unpredictable to adequately protect tubes. While grid protection is generally not
required with tubes like the 3-500Z, Ameritron does offer an optional fast-acting electronic circuit
that will rapidly disable the amplifier if excessive grid dissipation occurs. This circuit also reduces
or eliminates the chance of tank component damage from incorrect loading or a load failure. The
part number of this add on board is 50-01172-1.