AL-800H Instruction Manual
9
The continuous commercial plate current rating of each 3CX800A7 is 600 mA. Brief periods of plate
current exceeding 1.5 amperes (per pair) will not cause loss of emission or shorten the life of the tubes in
this amplifier. For maximum tube life, plate current should be maintained below 1.3 A on normal amateur
CW operation, 1.2 A on FM, RTTY, and other "steady" carrier modes.
The application of heater or filament voltage causes thermal stresses from rapid and uneven temperature
changes in the tube's heater. Avoid unnecessary main power switch cycling to prevent needless heater life
reduction.
An accumulation of gas (or stray debris) in the tube can cause the tube to arc between the anode and the
other elements of the tube. The resulting "gas arc" will generally manifest itself as a loud "pop" when the
amplifier is first turned on, or during conditions of high anode voltage. A "gas arc" will often damage diode
D117 on the negative rail of the filter capacitor bank and open the fuses in the amplifier. If this problem
occurs frequently, the tubes should be tested or replaced. The use of low quality tubes, tube that have been
stored for extended periods, or abused tube will increase the likelihood of a "gas arc". Ameritron
recommends using only current code date Eimac 3CX800A7 tubes.
Export Modifications
A simple modification will allow operation on frequencies above 15 meters. Instructions for this
modification are available by sending a written request for "Export Modification Instructions" along with a
copy of a valid amateur license. There is no charge for this information. Export models are shipped with
this modification installed and have an "X" or "Y" following the serial number. Standard frequency ranges
are indicated in the chart on page 19.
