QRP Labs QCX 50W Amp User manual

QCX 50W Amp
50W HF QCX Power Amplifier kit assembly manual
A low-cost, 50W Power Amplifier for the QCX with Full-
break-in (Q K) solid state Tx/Rx switching
PCB Rev
Designed and produced by QRP Labs, 019
  1

Contents
 !"
!#$$%&&$'%(#$%$&"
)&&$'%(
)*+
)!*,-.*/-0*12
))/-/-/1202*/31**)
)"/-/-/%145*/-2,1*%+)
)/-/-/%145*/-2,1*%"/-%6"
)+/-/-/7**/31**!"
)6/-/-/*7**/31**6
)8/%145*,0,1*"/-89
)9/%145*,0,1*/-!!
)/%145*,0,1*9/-!!
)/%145*,0,1*9/-!!!
)!/,0,1*:!:):+:6:)/-+!!
))/,0,1*"/-!)
)"/,0,1*8/-!)
)/-1-!:":+:8:9/-!"
)+/-1-:):/-6!"
)6//-2,1*%:!:)::8:9/-!
)8/*1*6:::"/-6!
)9/*1*!+
)!/*1*+!+
)!/*1*8!6
)!!/*/1*)!6
)!)/*/1*"!8
)!"/*/1*/-+!8
)!/!9
)!+/*1*:+/-9!9
)!6/*1*!/-))
)!8/*1*))
)!9/*1*!/-")
))/***1*)
))/,0,1*/-6)!
))!/,1//,1*";14*/)!
)))/,1//,1*!;<=))
))"/,1//,1*/-);5//-2))
))/%$/-!)"
  2

"$%&$;*/1*/>1/)
$%&$/>1/)6
+$%"!
+&,?>,"!
+!/02@/21*""
+)14*07*""
+"?*,1/-*>1/
+%145*!
++*/A, 4,?/.)
607*B20/-10*>1/+"
6*,2>1/+"
6!14*200+
6)1//,>1/1+
6"-C2/++
6&200 1. 2/-014*1202++
8'2*/+6
814*1202 &200 1.+6
8!%145*,?*,*>,+8
8)D/./ 10+8
9E*1/F1* +9
  3

1. INTRODUCTION – PCB Rev
This 50W QCX Power Amplifier has the following features:
Up to 50W power output with 20V supply, falling to around 25W at 13.8V supply
tandard 50-ohm input and output
Fast clean solid-state Tx/Rx switching provides full break-in operation (Q K)
Can be built for one of 80, 40, 30m or 20m bands with the supplied components (or other
bands with suitable choice of Low Pass Filter components)
Uses two low-cost IRF510 transistors as the power amplifier in push-pull configuration
Recommended amplifier operation in Class C
On-board 7-element Low Pass Filter for harmonic attenuation
Two black anodized heatsinks sized 130 x 28mm with 25mm fins typically limit the
temperature rise to < 20C over ambient in normal CW operation
Through-hole plated PCB, all through-hole components (no urface Mount Devices)
All connectors board-mounted: two BNC, one 2.1mm barrel power connector, one 3.5mm
jack connector for keying
PCB size 130mm x 59.5mm (2.744 x 1.338 inches)
tandard inexpensive components throughout (easy to replace)
Optional black anodized aluminium enclosure
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.
Note that this amplifier is NOT designed for Linear operation; linear operation would
require a higher bias current setting on the PA transistors and would result in higher heat
dissipation; it may be worthwhile experimenting with this but you will be in experimental
territory.
This amplifier is intended for single-band operation and may be built for 80, 40, 30 or 20m using
the supplied components. The band-specifying section of the circuit is the Low Pass Filter (LPF).
You may build it for other bands by suitable choice of low pass filter components; the LPF
component values should be the same as in the QCX kit http://qrp-labs.com/qcx, or the QRP Labs
LPF kit http://qrp-labs.com/lpfkit. T50 sized toroids must be used, and NP0/C0G type capacitors
with at least 100V rating, sufficient to handle the 50W output power.
A suitable power supply is required, for full power 50W operation it will need to be capable of
providing at 20V at a current of around 5A.
. GENERAL ASSEMBLY GUIDELINES
Assembly of this kit is quite straightforward. But there are quite a lot of components. o 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 jeweler'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 jeweler's loupe (like this one I use), right after soldering. This way
  4

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
possible (immediately after soldering the incorrect component). Again, a reminder: removing a
component and re-installing it later is often very difficult!
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 ground-
plane by what are called “thermals”, a gap between the pad and the ground-plane which is bridged
in 4 places at 0, 90, 180 and 270-degree around the circle. This is standard practice. However,
you may TILL 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. o please check and recheck, particularly with ground
connections.
The following tools are required: good soldering iron, preferably 50-60W; wire-cutters; screw-
drivers; electrical insulation tape; Digital Volt Meter (DVM) or similar for continuity testing; marker
pen.
3. ASSEMBLY
Deburr the ferrite rings and tubes by gently but firmly scraping them with a pair of wire-cutters or
similar as shown. This should smooth any sharp edges and reduce the risk of cutting the insulation
of the enameled wire.
Refer to the parts list and accompanying photographs, carefully inventory the components and
familiarize yourself with the kit contents.
  5

3.1 Parts list
This parts list shows the through-hole components to be inventoried and installed in the assembly.
Resistors
R1, 6, 9 1K 1W, brown-black-red-gold OR
brown-black-black-brown-brown (3pcs)
R2, 4 330-ohm, 2W, orange-orange-brown-gold OR
orange-orange-black-black-brown (2pcs)
R3 22-ohm, 2W, red-red-black-gold OR red-red-black-gold-brown
R5 4.7K trimmer potentiometer
R7, 10, 11, 14, 17 10K, ¼W, brown-black-black-red-brown (5pcs)
R8 470K, ¼W, yellow-purple-yellow-gold OR
yellow-purple-black-orange-brown
R12, 13 470-ohm, 2W, yellow-purple-brown-gold OR
yellow-purple-black-black-brown (2pcs)
R15 1.5K, ¼W, brown-green-red-gold or
brown-green-black-brown-brown
R16 470-ohm, ¼W, yellow-purple-black-black-brown
Capacitors
C1, 2, 3, 6, 7, 13, 16 1uF, 50V, code “105” (7pcs)
C4, 5 22nF, 50V, code “223” (2pcs)
C8, 10 47pF, 250V, code “470” (2pcs)
C9, 11, 12, 14, 18, 19, 20, 21 Band-dependent capacitors, see text
C15, 17 0.33uF, 250V, code “334” (2pcs)
180pF, 250V, code “181” (2pcs) – not used in 40m kit
270pF, 250V, code “271” (2pcs) – not used in 20m kit
390pF, 250V, code “391” (2pcs) – not used in 40m kit
680pF, 250V, code “681” (2pcs) – not used in 20m kit
Semiconductors
D1, 3, 5, 7 1N4007 (4pcs)
D2, 4, 6, 8, 9, 10 1N4148 (6pcs)
D11 3mm green LED
D12 3mm red LED
Q1, 2 IRF510, TO220, MO FET (2pcs)
Q3 FQPF2N60C, TO220, MO FET
IRFU9024 IRF9530, MO FET
Q5, 6 B 170, TO92, MO FET (2pcs)
IC1 78L05, 5V voltage regulator
Inductors
L1, 2, 3, 5, 8, 9, 10 47uH molded inductor, yellow-purple-black-silver (7pcs)
L4, 6, 7 T50-6 toroid, yellow, (3pcs)
T1, 2 Ferrite toroid, black (2pcs)
T3 Made from 2pcs ferrite tube (black)
Miscellaneous
PCB 130 x 59.5mm PCB, double-sided through-hole-plated FR4
1mm diameter wire Enameled wire (40cm)
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0.6mm diameter wire Enameled wire (320cm)
X1, 3 BNC Connector (2pcs)
X2 3.5mm stereo jack socket
X4 2.1mm DC barrel power connector
Pad TO220 insulating silicone pad (2pcs)
Insulating washer 2pcs white plastic insulating washer
9mm M3 screw Pan-head screw (2pcs)
6mm M3 screw Pan-head screw (4pcs)
Heatsink 130mm x 28mm x 25mm deep (2pcs)
Enclosure kit (OPTIONAL)
Enclosure 63w x 25h x 130d mm enclosure, drilled, cut and engraved
crew Enclosure front and rear panel mounting screws (8pcs)
Feet elf-adhesive rubber cabinet feet (4pcs)
The main 50W Amplifier kit bag contains the PCB, two smaller bags of components, and one small
plastic box. The plastic box contains the powdered iron toroidal and ferrite cores, in order to
prevent breakage during shipping.
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3. Trace diagram and parts layout
Red = Top side; Blue = bottom side; Green = pads.
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.
3.3 Wind and install output transformer T3
We start with the installation of the transformers and inductors, which are generally the most
difficult components; doing these first means we have space around them so it is easier to access
the wires etc.
First is the output transformer, T3. The windings are made from the thick, 1mm diameter
enameled copper wire. They are wound on the two ferrite tubes, which are placed side-by-side to
make a large binocular core.
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