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Exhibit 6 page 20 of 33
5.3. Tuning of Power Amplifier
The OM2500A amplifier is operated in class AB. Thus it’s possible to obtain a maximum
output power at excellent linearity. For this purpose the amplifier has to be tuned carefully.
WARNING!
Before starting tuning you have to check if the right antenna or a 50 Ohms load
resistance is connected at the antenna output!
CAUTION
The operation of a mistuned PA will cause malfunctions, the increase of grid current
(the GRID-MAX-LED will light up) and problems with TVI/BCI.
CAUTION
The grid-current is shown with 2 LED diodes. It’s normal if the green LED is flashing or
may be shining a little bit during peak operation. If you overload the amplifier the
output power increases the grid current at very small rates and the red GRID-MAX-
LED is shining and the safety devices switch the PA to STBY. You must decrease the
input power.
CAUTION
In SSB mode you will have good output power if the green LED lights up a bit. The
current of screen grid is measured and shown in a Bar graph Indicator. The amplifier
has to be tuned in such a way that the current is between - 20 mA to +50 mA. At
currents beyond these values the operating point will be shifted and IM-products will be
rapidly increased. If a value of + 70mA is exceeded, the safety devices will switch the
amplifier to STBY mode.
5.3.1. Manual Tuning
1. Set the multimeter switch to the HV position
2. Set the OPR/STBY switch to the STBY position
3. Press the ON button
The amplifier is prepared for operation with the following automatic steps:
The toroidal transformers are switched on step by step.
The cooling blower for the final tube is switched on.
The multi-meter bar graph measures the high voltage; the normal value is 2.8 kV
The WAIT LED lights up
CAUTION
After switching on, please confirm that the blower is operating properly. Air must be
flowing from the ventilating aperture above the tube. If there is any concern, or no air
flow, press the “OFF”-button immediately !
Heating the tube takes about 150 seconds. After this time the WAIT LED goes out and the
amplifier is ready for operation.