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3. During the preliminary tuning, switch PTT on and off several times, to allow time for tube cooling. The tube
dissipation (at a given drive level) is minimum when tuning is optimum. In short, be brief, with tuning "bursts".
4. Preliminary tuning, as described above, is only necessary when operating for the first time in a certain band.
When the final settings for PLATE and LOAD have been found for the particular working conditions -
especially the antenna used, note your settings on Table 1. The new settings will normally differ to some extent
from the ones indicated, depending on the “resistance and reactance" of your antenna load.
5. If less than maximum power is run, it is possible that the Ig2 indication remains green and never goes into
red.
10.1.3 Final tuning
Once the preliminary tuning has been done for each band / antenna combination, the values found for PLATE
and LOAD can be used for final tuning, with no need to repeat the preliminary tuning every time.
Tuning for full power
•
Start with low drive level and the PLATE and LOAD knobs in the known initial positions.
•
Put PTT ON and increase the power (fairly quickly), to the onset of the overdrive indication. If the
screen current (red Ig2) goes too high, adjust LOAD, by turning the knob to the left – towards lower
numbers on the dial (increasing the load).
•
Adjust the drive level and LOAD until the overdrive indicator is just about to turn ON, and at the same
time Ig2 shows two or three red LED's ON.
•
Fine tune PLATE for maximum output and maximum Ig2. Repeat the step above if required.
•
When the desired tuning level is achieved on a band, record the plate and load numbers in the ‘Users
Settings’ of Table 1.
NOTE
: A flashing red Ig2 indicator, even for a long time, is not harmful to the tube, since Ig2 is limited to a
safe value.
Tuning for less than full power
NOTE: Low output power could create more tube plate dissipation then the normal / full output.
•
Start at low power, with the initial values for PLATE and LOAD
•
Put PTT ON and apply drive until the output is about 1/2 of the desired power.
•
Adjust LOAD for maximum output. Most likely, the knob will have to be rotated clockwise, towards
higher numbers on the dial.
•
Adjust PLATE for maximum output
•
Apply more power
•
Repeat the 3 steps above until the required power is achieved. If screen current is indicated by Ig2, it
should display two to four red LED's. Maximise this Ig2 indication (and the output power at the same
time), by tuning PLATE
Please note that the tuning at lower power is different from the setting at full power (especially LOAD).
•
If the output goes higher then desired, reduce the drive
and re-tune
.
Never reduce the output by de-
tuning the amplifier
!
NOTE
: If the output is low (say, less than about 2000W), Ig2+ will never show any screen current at all. Ig2
might even indicate a negative current, in green - this is normal and is no cause for concern.
