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If there is green Ig2- indication, for a given input drive, try to minimise it and even to obtain red indication. For
this, it is likely that LOAD needs to be moved clockwise, followed by PLATE retuning. If red indication is
achieved, try to maximise it by tuning.
With low drive / low output it is likely the Ig2 indication to be green, increase as more drive is applied, then
decrease and become red at higher output.
10.1.4 Potential problems during tuning
The tuning operation should be completed fairly quickly. If the tuning process takes a longer time, it should be
done by switching the transmission on and off several times, to allow the tube time to cool.
•
If the FAULT light comes on, it is possible that the plate current has reached too high values due to
incorrect plate tuning. In this case, reduce the excitation power, wait for the FAULT light to turn off
(about 2 minutes) and resume tuning.
•
If the overdrive protection is activated, by cutting off the amplifier for 2 seconds. It is likely in this case
that you are applying too much power at the input. Reduce the power and watch the "overdrive" LED.
Increase the power only until this light starts flashing.
•
If the overdrive protection is activated at low power – this could be due to incorrect loading. Turn the
LOAD control clockwise and tune PLATE. Increase the drive and repeat in small steps.
•
If the SWR protection cuts in – it is likely to be a problem with either the feedline, antenna or associated
antenna switching components. In principle, the SWR protection level in DX-3SP is adjustable, but it is
far preferable for you to fix your antenna system.
10.2
USING YOUR DX-3SP
While tuning and adjusting the amplifier, a CW mode is normally used. When these operations are finished, you
can change to the operating mode you wish to use and start operating.
10.2.1 CW / RTTY and all digital modes
In CW, the setting up of the amplifier is similar to that of the tuning mode. After adjusting the input power level
to the amplifier, according to the desired output level, and tuning the plate and load capacitors, you can simply
start operating by applying the same carrier level as during tuning. If the amplifier is set to deliver full output
power, or close to, then screen current will be present (red Ig2). As in the case of tuning, the best operation is
achieved when there is a certain amount of screen current flowing, corresponding to two to four red LED's
turning on in the Ig2 display.
10.2.2 Voice modes (SSB)
When a voice modulation is applied to the amplifier, the drive level is not precisely defined, as in the case of
tuning with continuous carrier. If there is screen current flowing, or an input overdrive, they will be indicated
only at peak of modulation, by the respective indicators flashing. The Ig2 indicator is likely to flash both green
and red. You will have to adjust the microphone gain, or the RF drive, or both, in an attempt to achieve peak
input driving conditions similar to those you have used while tuning. Occasional flashing of the overdrive
indicator is acceptable. If the over-driving is severe, a momentary cut-off will occur.
