Specifications

Alpha 9500 HF Linear Amplifier Operating Manual Alpha Radio Products
Maintaining and Upgrading the Amplifier Product Release 1
DOCNUMBER 9500
Document Issue 1, Revision 7
Page 8–2 June 2009
88
8
Step 6 Replace the cover and reconnect the AC line cord to the power source.
8.2 Retune the Amplifier
Normally you need retune the amplifier only if you change radios,
antennas, or some other aspect of your shack.
When the amplifier is first keyed (that is, moved into State 5) and RF is
sensed, it measures the signal frequency, moves to the appropriate band
and segment, and sets the tune and load-capacitor positions to the values
that you saved for that frequency. If you saved a different antenna position
for that band, it selects the new position.
Your objective in tuning the amplifier (and the drive applied to it) is to
obtain optimum efficiency and linearity at the desired output power. You
must adjust the amplifier for optimum efficiency and linearity at each
specific power level. If you attempt to operate at higher or lower power
levels than those for which you have adjusted, the following happens:
•
At higher power, the amplifier flattops, splatters, and (usually)
produces excessive amplifier grid current.
•
At lower power, the amplifier decreases efficiency considerably.
The ALPHA 2100 in-line dummy load simplifies this adjustment process
by enabling you to switch between dummy load and antenna at the flip of
a switch.
At the factory, the amplifier is tested and tuned into an ALPHA 2100, 50-
ohm dummy load and the correct tune and load capacitor values are stored
into the default memory-segment positions. You must retune the
amplifier for your particular station setup and save those settings to the
user memories. After the amplifier has switched to the correct tune and
load settings for that particular frequency, you may touch up the capacitor
settings to achieve maximum output.
Procedure 8-2 Retune the amplifier
Step 1 Tune the amplifier for your station setup.
Output tuning on the amplifier is set to broadband and to change
frequencies by up to 100 kHz. They should not normally require retuning.
One-pass auto-tuning is engaged when you press the MEMORY/AUTO
button and the output power is above 150 W. The autotune algorithm
varies the capacitor tune and load settings while paying attention to grid
and plate current to achieve maximum efficiency. The amplifier operates
most efficiently at 1500 W of output power, although it can easily operate
at lower levels.
Step 2 Save the settings to user memories.