QRP Labs 10W HF Linear PA, Инструкция по сборке

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10W HF Linear PA kit assembly 1.00
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4 Applications information
4.1 PA Precautions
To avoid dramatic failure of components, observe the following precautions:
1) Check all the components again, and again, BEFORE applying power to the amplifier!
Check the resistors are in the correct places, check that all the enamelled wire inductors
and transformers are properly soldered with continuity through the windings. Check that the
capacitors are installed correctly (with the correct polarity). The same applies to diodes,
transistors and the voltage regulator IC. Pay particular attention to ground connections of all
components: A very common fault is failure to apply adequate heat to ensure a good solid
joint to ground
– the groudplane will dissipate heat and draw it away from the joint.
2) Before applying power, make sure the two trimmer resistors (PA bias) are turned all the
way anticlockwise.
3) Check for short-circuits between the IRF510 metal tab, and ground! Check that there are no
other shorts, the DC resistance between the +12V tab and Ground should not be near zero.
4) Do not apply power to the amplifier unless the heatsink installation has been performed and
all screws are tightened.
5) Always use a Low Pass Filter between the Amplifier output and your antenna system.
6) On first powering up the amplifier, and during adjustments, use a current-limited supply. If
anything does go wrong, you’ll have more time to notice it before letting the smoke out.
4.2 Connections
This amplifier has 50-ohm RF input and outputs. It requires a good solid DC power supply of 12V
to 14V capable of supplying up to 2.5A current. Use thick wires to connect the power supply to the
amplifier, to avoid unwanted voltage drop.
Keep the input RF away from the output RF. These connections are at opposite ends of the board,
to avoid unwanted feedback which could result in instability.
The /TX input connection switches on the bias to the PA transistors. This is an Active Low input: it
should be driven to Ground to switch on the bias.
4.3 Adjustment
The only adjustments required are the two trimmer resistors which set the final PA transistors
(IRF510) bias currents. Make sure the trimmer resistors are initially turned all the way
anticlockwise.
Apply power, while observing the current consumption. You can do this with a power supply with
current metering, or using a DVM in series with the power supply.
Connect the /TX input to ground, to switch on the amplifier. Do not apply any input RF at this
stage.