RF Concepts LLC PA-77DF User Manual

88

DOCNUMBER 9500

Document Issue 1.1
February 2010

Page 8–9

RF Concepts, LLC

Alpha 9500 Linear Amplifier User Manual

Product Release 1

Diagnosing Faults

3. Ensure that the external fan is operating. The fan is at the right rear of 

the amplifier, covered by a wire grill. It should start to rotate in the 
ON AMP condition. Use a flashlight if necessary to avoid the 
appearance of nonrotation due to the stroboscopic effect. This can be 
done without removing the amplifier cover.

4. Check the internal airways of the amplifier. Unplug the amplifier, 

remove the cover, and ensure that the blower motor (to the right of the 
tube) is clean and that its impeller rotates when moved gently with a 
long screwdriver. Look down into the tube and ensure that the 
passages between the anode fins are not blocked, for example by an 
accumulation of dust.

5. Ensure that amplifier is being operated with a tuning condition that 

does not result in poor efficiency.

6. Ensure that the tube standing bias (keyed, with no RF) is not greater 

than 500 mA. Key the amplifier with the meter set to Ip to make this 
measurement. If Ip is greater than 500 mA, then there may be a 
problem in the cathode bias circuitry, on the cathode board, or in the 
tube itself.

Reflected power too high.

The amplifier monitors the apparent reflected power at its output. If the 
power is above the set value, currently 375 W, the amplifier goes into 
BYPASS mode and attempts to clear the fault.

•

Ensure that antennas and other equipment installed after the amplifier 
were installed correctly.

Clear over-temperature.

The amplifier has recovered from fault 11 (temperature fault).

•

See fault 11.

Plate voltage too high.

The plate voltage has exceeded a safe value, currently 3800 Vdc.

1. Ensure that the AC mains voltage is correct.