QRP Labs 10W HF Linear PA User manual

10W HF Linear PA kit assembly 1.00 1
10W HF Linear PA
10W HF Linear Power Amplifier kit assembly manual
A low-cost, high-performance HF Linear PA
covering 2-30MHz
Designed and produced by QRP Labs, 2018

10W HF Linear PA kit assembly 1.00 2
Contents
1. Introduction ..............................................................................................................................................................3
2. General Assembly guidelines ....................................................................................................................................3
3 ASSEMBLY .................................................................................................................................................................4
3.1 Parts list.............................................................................................................................................................4
3.2 Trace diagram and parts layout ........................................................................................................................7
3.3 Schematic..........................................................................................................................................................9
3.4 Wind and install inductor L201.......................................................................................................................10
3.5 Wind and install transformer T201.................................................................................................................11
3.6 Wind and install transformer T202.................................................................................................................13
3.7 Wind and install transformer T203.................................................................................................................14
3.8 install capacitor C213......................................................................................................................................16
3.9 Wind and install transformer T204.................................................................................................................16
3.10 Install capacitors C211 and C212....................................................................................................................18
3.11 Install remaining ceramic capacitors ..............................................................................................................18
3.12 Install inductors L202, L203, L204 and L205...................................................................................................19
3.13 Install resistors R203, R204, R209, R210.........................................................................................................19
3.14 Install resistors R201, R216 and R217.............................................................................................................20
3.15 Install resistors R207 and R208.......................................................................................................................20
3.16 Install resistors R213 and R218.......................................................................................................................21
3.17 Install resistors R212 and R214.......................................................................................................................21
3.18 Install resistor R202.........................................................................................................................................22
3.19 Install resistor R205.........................................................................................................................................22
3.20 Install resistor R206.........................................................................................................................................23
3.21 Install trimmer resistors R211 and R215.........................................................................................................23
3.22 Install capacitor C204......................................................................................................................................24
3.23 Install capacitor C214......................................................................................................................................24
3.24 Install diode D201 ...........................................................................................................................................25
3.25 Install transistor Q201.....................................................................................................................................25
3.26 Install transistors Q202, Q203 and Q204........................................................................................................26
3.27 Install transistors Q206 and Q209 ..................................................................................................................26
3.28 Install transistor Q205.....................................................................................................................................27
3.29 Install voltage regulator IC201........................................................................................................................27
3.30 Install transistors Q207 and Q208 ..................................................................................................................28
3.31 Install heatsink ................................................................................................................................................30
4 Applications information ........................................................................................................................................32
4.1 PA Precautions................................................................................................................................................32
4.2 Connections ....................................................................................................................................................32
4.3 Adjustment......................................................................................................................................................32
4.4 Tests undertaken ............................................................................................................................................33

10W HF Linear PA kit assembly 1.00 3
1. Introduction
This 10W HF Linear Power Amplifier has the following features:
•10W output from 2 to 30MHz, using 12V Supply
•Generously-sized heatsink, will not overheat even on continuous 100% duty-cycle modes
•2-stage amplifier provides 26dB of gain
•Push-pull driver and push-pull finals, for high linearity and low harmonic content
•+/- 1dB gain flatness from 2 to 30MHz
•4dB down at 4m (50MHz) and 8dB down on 4m (70MHz)
•Standard 50-ohm input and output
•Through-hole plated PCB, all through-hole components (no Surface Mount Devices)
•Standard inexpensive components throughout
•Tested for 1 hour at full-power 10W, 100% continuous duty-cycle with no forced air cooling
•Tested for 15 minutes at 20W, 100% continuous duty-cycle with no forced air cooling
•Tested at 20V supply
•Tested into open load, shorted load and various mismatches
We hope you enjoy building and operating this kit! Please read this assembly manual carefully,
and follow the instructions step by step in the recommended order.
The push-pull driver stage using two BS170’s is as used in the SoftRock transmitter stage.
I am very grateful to Allison KB1GMX for very valuable advice during the design and
development of this amplifier, for beta-testing prototypes, measurements and moral
support!
2. General Assembly guidelines
Assembly of this kit is quite straightforward. But there are quite a lot of components. So please
keep them methodically in trays or some convenient storage boxes. Be careful not to misplace
any. The usual kit-building recommendations apply: work in a well-lit area, with peace and quiet to
concentrate. Some of the semiconductors in the kit are sensitive to static discharge.
Therefore, observe Electrostatic discharge (ESD) precautions. And FOLLOW THE
INSTRUCTIONS!! Don’t try to be a hero and do it without instructions!
A jeweller’s loupe is really useful for inspecting small components and soldered joints. You’ll need
a fine-tipped soldering iron too. It is good to get into the habit of inspecting every joint with the
magnifying glass or jeweller’s loupe (like this one I use),
right after soldering. This way you can easily identify any
dry joints or solder bridges before they become a
problem later on when you are trying to test the project.
Triple check every component value and location
BEFORE soldering the component! It is easy to put
component leads into the wrong holes, so check, check
and check again! It is difficult to de-solder and replace
components, so it is much better to get them correctly
installed the first time. In the event of a mistake, it is
always best to detect and correct any errors as early as

10W HF Linear PA kit assembly 1.00 4
possible (immediately after soldering the incorrect component). Again, a reminder: removing a
component and re-installing it later is often very difficult!
Components in the kit are installed vertically, to minimize PCB area and track-lengths. You will
need to bend the resistor wires as shown in the picture below. On the parts layout diagram, there
is a small circle around the hole where the body end of the resistor should be installed. This is not
critical (resistors don’t care which way around they are) but it is recommended, just to try to ensure
that the folded over wire-end of the
resistor doesn’t touch any other
wire or metal part.
Please refer to the layout diagrams
and PCB tracks diagrams and
follow the steps carefully.
The component colour coding of the layout diagram at every step of the assembly instructions is
as follows (kind of: components past, present and future):
•Components shaded grey have already been installed
•Components shaded red are the ones being installed in the current assembly step
•Components shaded white are the ones which have not yet been installed
VERY IMPORTANT SOLDERING ADVICE: when soldering a component pin that goes to ground,
you need to allow extra time with the soldering iron. Ground pads are separated from the
groundplane by what are called “thermals”, a gap between the pad and the groundplane which is
bridged in 4 places at 0, 90, 180 and 270-degree around the circle. This is standard practice.
However, you may STILL find that it is harder to solder ground connections, because the soldering
iron heat is dissipated away more quickly. If a component ground connection is broken it can
sometimes have catastrophic consequences. So please check and recheck, particularly with
ground connections.
3 ASSEMBLY
The PA board is mounted vertically on the rear PCB’s back edge. The PA transistor tabs and the
driver are bolted directly to the substantial heatsink provided in the kit.
Use a drill bit, twisted by hand, in each hole of the binocular cores, just to remove any
sharp edges, and prevent scratching the wire enamel.
NOTE: The two BN61-2402 binocular cores are supplied in a small labelled bag. This is
because they are visually identical to the BN43-2402 binocular core. Do not remove the
BN61-2402 from their small bag, or you would risk mixing them with the BN43-2402.
3.1 Parts list
This parts list shows the through-hole components to be inventoried and installed in the assembly.
Resistors
R201, 216, 217 220-ohm ¼W, red-red-black-black-brown (3pcs)
R203, 204, 209, 210 220-ohm ½W, red-red-black-black-brown (4pcs)
R202 22K, red-red-black-red-brown

10W HF Linear PA kit assembly 1.00 5
R205 2.2K, red-red-black-brown-brown
R213, 218 10K, brown-black-black-red-brown (2pcs)
R212, 214 47-ohm, yellow-purple-black-gold-brown (2pcs)
R207, 208 2.2-ohm, red-red-black-silver-brown (2pcs)
R206 33-ohm, orange-orange-black-gold-brown
R211, 215 4.7K trimmer potentiometer, label “472” (2pcs)
Capacitors
C201 - 203, 205 - 210, 215 0.1uF, code “104” (10pcs)
C204 10uF 25V electrolytic
C214 470uF 25V electrolytic
C211, C212 1uF, code “105” (2pcs)
C213 33pF, code “330”
Semiconductors
D201 1N4004
Q201 2N3904
Q203, 203, 204, 205 BS170 (4pcs)
Q206, 209 IRFU9024, substitute for BS250 (2pcs)
Q207, 208 IRF510 (2pcs)
IC201 78L05, 5V voltage regulator
Inductors
L201 BN43-2402 binocular core
L202, L203, L204, L205 1uH molded axial inductors
T201, 202 BN61-2402 binocular core (2pcs, separate bag)
T203 FT50-43 toroidal core
T204 BN43-202 binocular core
Miscellaneous
PCB PCB
Insulated wire 30cm of insulated wire
0.6mm wire 80cm of 0.6mm enamelled wire
0.4mm wire 15cm of 0.4mm enamelled wire
0.25mm wire 60cm of 0.25mm enamelled wire
Insulating silicone pad Insulating heatsink silicone pad (3pcs)
M6 nut M6 nut
Washer Large washer
Insulating washer 2pcs white plastic insulating washer
9mm M3 bolt 9mm M3 bolt
15mm M3 bolt 15mm M3 bolt
Rubber tube Short ~4mm length of rubber tube
Heatsink Custom-manufactured 130x28x25mm

10W HF Linear PA kit assembly 1.00 6

10W HF Linear PA kit assembly 1.00 7
3.2 Trace diagram and parts layout
Red = Top side; Blue = bottom side; Green = pads and vias.
There are only two layers (nothing is hidden in the middle). Not shown in these diagrams are the
extensive ground-planes, on both sides of the board. Practically everything on both layers that isn’t
a RED or BLUE track, is ground-plane! The two ground-planes are connected at frequent intervals
(not more than 0.1-inches) by vias.

10W HF Linear PA kit assembly 1.00 8

10W HF Linear PA kit assembly 1.00 9
3.3 Schematic

10W HF Linear PA kit assembly 1.00 10
3.4 Wind and install inductor L201
Start with the inductors and transformers because they are difficult to install when the other
components are all around them.
The BN43-202 core is the one NOT in the small plastic zip-lock bag. First use a drill bit twisted
by hand, to gently remove any rough edges to the holes, that could cut into the wire.
L201 is a simple inductor made of 4 turns of the 0.4mm (Medium thickness) wire wound around
the BN43-2402 binocular core. “One turn” means the wire goes through both holes. The start and
end wires of the toroid wire therefore are both on the same side.
Install it on the PCB, cut the wires to 2mm and as usual, solder it for at least 10 seconds to ensure
the enamel burns off.
Test for DC continuity between the 12V pad of the PCB (indicated in the black circle) and the
positive pad of capacitor C204 (indicated in the red circle).