QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 1
QPA-1
QPA-1 Low level input QRP HF Amplifier
and CW TX (3 a 30MHz)
Assembly manual
Last update: May 1, 2018
ea3gcy@gmail.com
Most recent updates and news at: www.ea3gcy.com
Thanks for constructing the QPA-1 Amplifier kit
Have fun assembling it and enjoy QRP! 73 Javier Solans, ea3gcy
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 2
SPECIFICATIONS
Bandwidth: 1 to 35MHz.
Input power max. (no attenuator): 0dBm 50ohms.
Minimum gain: 37dB@14MHz 13.8V (in 0dBm out 5W/14MHz 8W/7MHz)
Output Power: up 15W
Supply: 12 to 14V
PCB Size: 55 x 40mm
PARTS LIST
Qty
Reference
Value
Component type
Identification
1
R14
1
1 Ω resistor
brown-black-gold
1
R2 (input attenuator)
1 (see text)
1 Ω resistor
brown-black-gold
2
R9, R10
47
47 Ω resistors
yellow-violet-black
1
R12
100
100 Ωresistors
brown-black-brown
4
R4, R7, R8, R17
330
330 Ωresistors
orange-orange-brown
3
R5, R6, R16
1K
1K resistors
brown-black-red
2
R1, R3 (input attenuator)
See text
1
R15
4K7
4K4 resistor
yellow-violet-red
2
R11, R13
100K
100K resistor
brown-black-yellow
1P15K
5K Adjustable resistor
503 - 53
6
C1, C2, C3, C5, C6, C9
10n
10n capacitors
103 or 0.01
7
C7, C10, C11, C12, C14,
C15, C16
100n
100n capacitors
104 or 0.1
3
C4, C8, C13
100uF
100uF electrolytic capacitors
100uF
1Q1BC557/558
BC557 or BC558 PNP transistor
BC557/558
1Q22N3819
2N3819 Fet tansistor
2N3819
3
Q3, Q4, Q5
BS170
BS170 Fet transistors
BS170
1Q6RD16HHF1
RD16HHF1 Power amp transistor
RD16HHF1
1
Q7 (see text)
--
(see text)
--
1D16V2
Zener diode 6V2
6V2
1L1FT50-61
FT50-61 toroid 10 x 2 turns (see text)
FT50-61
43cms
Enamelled wire
--
43cms enamelled wire for L1 toroid
--
8
Terminal-pins
--
Terminal-pins 2 + 2 + 2 + 2
--
4
Spacers+screws+nuts
--
Hex spacers + M3x4 screws + M3 nuts
--
1
Heatsink
--
RD756 Heatsink for Q6 (Power Amp)
--
1
QPA-1 PCB
--
QPA-1 board
--
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 3
PLEASE READ ALL OF THE ASSEMBLY
INSTRUCTIONS COMPLETELY AT LEAST ONCE
BEFORE BEGINNING.
TIPS FOR FIRST TIME BUILDERS
Tools required:
- A 30W soldering iron with fine tip, small wire cutters for cutting component leads, wire strippers, longnose pliers, needle-nose pliers, X-Acto knife, screwdriver for M3 screws, alignment tool for adjusting IF
transformers.
- You will need a good light and a magnifying glass to see the fine print on the components and other
assembly details.
Instruments required:
- Multimeter, oscilloscope (desirable but not essential), frequency counter or HF receiver, RF power
meter, dummy load: 5W - 50 Ohms.
Soldering:
There are two important things which need to be done to insure successful operation of a kit. The first is
to put the component into the proper place on the circuit board; the second is good soldering.
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 4
To solder properly, you must use a high-quality solder for electronics use and the correct type of iron.
Use a small soldering iron with a fine, pointed tip. The soldering iron should be about 30 watts (if it is not
thermostatically controlled). Use only high-quality electronic type solder. NEVER use any extra flux. You
should hold the hot soldering iron in contact with both the circuit board and the component lead for about
two seconds to heat them up. Then, keeping the soldering iron in place, touch the solder at the junction
of the lead and trace and wait about two seconds or so until the solder flows between the terminal and
the trace to form a good joint. Now remove the soldering iron. The soldering iron should have been in
contact with the work piece for a total time of about 4-5 seconds. After soldering each joint, you should
clean the soldering tip, removing any excess solder. This prevents mixing in old solder and residues from
previous soldering operations.
Finding the correct component:
Diodes
Be careful to observe the correct polarity of the diodes. There is a black band towards one end of the
diode. This band should be oriented towards the line printed on the component outline of the circuit
board.
Electrolytic capacitors:
These must be placed with the correct polarity. The positive lead (+) is always the long lead. The
negative terminal (-) is the short lead and is marked by a stripe on the body of the capacitor. Make sure
that the positive lead of the capacitor goes through the hole marked with a "+" on the circuit board.
Coils and transformers:
You may find it convenient to wind and prepare all the coils and transformers before beginning to mount
the components. That way you won't have to stop and possibly lose concentration while winding them.
This is the part of the construction that some consider to be the most difficult. I personally find it to be
one of the easiest stages, and it can even be relaxing. Look for the most appropriate moment to do it,
and most importantly, take your time. The drawings and instructions in the manual will illustrate and
accompany you in the process.
RECOMMENDED ASSEMBLY SEQUENCE
1.- The resistors are installed first. Mount all the resistors R1 to R13.
Install and solder P1
2.- Next mount the D1 diode, being careful to place them with the correct orientation. This is a band on
one end that corresponds to the component outline on the circuit board.
3.- There are ceramic and electrolytic capacitors. They all have their value printed on the body. Refer to
the “identified” column in the parts list. Install and solder all the capacitors C1 to C16
When you mount them, make sure to leave the leads as short as possible.
The electrolytic capacitors must be placed with the correct orientation: the LONG LEAD goes in the hole
labeled “+” and the SHORT LEAD is "-", indicated by a band containing "-" signs on the side of the
capacitor.
4.- Place and solder Q1 to Q5 transistors in place printed on the board. Your printed silhouette should
match the body of the transistor. Q6-Q7 will be installed later.
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 5
5.- Install the pins-terminals. Turn the board over and insert and hold the header in place, using a
“jumper” placed on the header while you solder the pins to avoid burning your fingers. Use your other
hand to hold the soldering iron and move the board towards the solder to solder the headers in place. If
you have someone available to help you, it will be much easier!
6.- The L1 Toroid will be wound as shown below.
L1 TOROID WINDING
L1 is an impedance matching transformer with a bifilar winding. An FT50-61 is used (black toroid with
12mm/0.5in OD). It has 10+10 turns.
- Cut a 42cm (17in) long piece of 0.5mm diameter enameled wire.
- Bend the wire in half.
- Twist it so that there are about two twists per cm.
- Before beginning to wind, leave 15-20mm of wire, measured from the end of the wires to the outer
edge of the toroid. Now wind ten (10) turns on the toroid. Remember: Count one turn for every time the
wire passes through the center of the toroid.
- Spread the turns evenly around the toroid.
- Cut the ends and separate the two windings.
- Use a sharp X-Acto knife to scrape the enamel off the ends that will be soldered. The ends of the coils
that we have made need to be prepared in this manner before soldering them into the board.
- Using a multimeter in its ohm or continuity function, locate and mark the ends, identifying them as “a” “a1” and “b” - “b1”.
- Mount the toroid into the appropriate holes as marked on the circuit board.
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 6
Note: For greater clarity, the drawing shows one black wire and one red wire. In reality, both wires are of
the same color.
MOUNTING THE POWER TRANSISTOR Q6
The printed circuit board of the QPA-1 allows the placement of two different MOSFET transistors: Q7
and Q6. The place of Q7 is for an IFR510 or equivalent and the place of Q6 is for an RD16HHF1.
In this kit we will use Q6 since the RD16HHF1 is a modern MOSFET transistor special for RF that offers
greater gain and efficiency than other transistors.
If you are going to use the QPA1 as a CW transmitter and with a moderate output power (about 5W
max.), then it will be sufficient to mount the Q6 with the radiator included in the kit. See the following
image.
Note: The body of the Q6 is connected to its "SOURCE" terminal. As this terminal goes to GND, the
transistor can be fastened with a screw without any insulation. It is advisable to use a little thermal paste
to help dissipate the heat.
Q6 mounted on the plate with the radiator
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 7
If you are going to use the QPA-1 every day as an amplifier or as a CW transmitter with output powers of
more than 5W, we recommend using a larger radiator or fasten the transistor directly in the metal box.
See the following image.
Q6 fastened in the metal box.
INPUT ATTENUADOR R1-R2-R3
The input of the QP1-A has an attenuating network formed by R1, R2 and R3.
If you use the ILER-DDS Kit based on the AD9850 DDS or another similar circuit that delivers a low level
signal (0dBm or less), place a 1Ω resistor in the R2 place and do not place anything in the R1 locations
and R3.
If the input signal is going to be higher than 0dBm, then we recommend using an attenuator with the
appropriate attenuation factor.
Even with attenuator, we DO NOT recommend the use of QPA-1 with input powers higher than 27dBm
(about 500mW). Use 1/2W resistors if necessary.
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 8
CONNECTIONS, ADJUSTMENT AND START
1.- The power supply 12 to 14V goes to “+” and “GND” terminals printed on board.
2.- Connect the signal source at the "INPUT" and the LPF low pass filter/filters at the "OUT" suitable for
the bands to be worked and a power meter with a load of 50 ohms on the output filters.
3.- The jumper formed by the terminals "TX/K" must be connected while transmitting and must be
disconnected when it is not transmitted (it feeds the "Idle" of the Q6 and should not be present while the
transistor is not working).
- If the QPA-1 is used as a CW transmitter, then the jumper terminals "TX/K" will be connected to the
telegraph key and the input signal can remain connected even if it is not transmitting.
- If QPA-1 is used as an amplifier for a SSB transmitter, CW or other signal sources, then the "TX/K"
jumper must be attached while transmitting and disconnecting when it is not transmitted.
Setting of "P1" - Terminal "TP" - Start-up
The only adjustment to be made is the "Idle" (Biasing) of the final transistor Q6 through the adjustable
resistor P1.
Note: Make this adjustment with the power transistor cool.
With no signal at the "INPUT", set the amplifier to TX (terminals "TX/K" connected) and set P1 until you
get about 4.5V at the "TP" test point.
Now inject the signal source into the "INPUT" and keeping the "TX/K" terminals together, the output
power should be within the expected levels in relation to the input.
Note that slightly varying the voltage present in "TP" will increase or decrease the output power. This is
because the polarization of the "Gate" of the transistor varies and the type of amplification of the
transistor and therefore its gain. It is not recommended to exceed 5V.
Important note: Carry out the adjustments and checks in small time intervals and check that the Q6
radiator does not reach a very high temperature.
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 9
LIMITED WARRANTY
Please read carefully BEFORE building your kit
All electronic components and hardware supplied with the kit are under warranty in case of any
manufacturing defect for the period of one year after purchase. The warranty does not include the
transmitter final amplifier transistor.
The original purchaser has the option of examining the kit and manual for 10 days. If, within this period,
the buyer decides not to build the kit, he/she may return the entire unassembled kit at their own expense
for the shipping expenses. The shipping expenses and sales commissions (i.e. bank, Ebay, and Paypal
commissions) included in the purchase price will not be returned.
Please, BEFORE returning a product, request instructions by email at: ea3gcy@gmail.com
Javier Solans, EA3GCY, warrants this device to function according to the specifications, provided that it
is assembled and adjusted as described in this documentation, and used correctly according to all
provided instructions.
It is your responsibility to follow all the instructions in the manual, to identify all the components correctly,
and to use good workmanship and proper tools and instruments in the construction and adjustment of
this kit.
REMEMBER: This kit will not work as a commercially manufactured product; however, if can often give
similar results. Do not expect great performance, BUT YOU ARE SURE TO HAVE LOTS OF FUN!
If you believe that there is a missing component for the kit, please do a thorough inventory of all parts
using the parts list in the manual. Check all bags, envelopes and boxes carefully. If needed, you may
email me and I will replace any component that you are missing. Even if you can find the exact part
locally, please let me know so that we are aware of the problem to help other customers.
I can also supply any part that you have lost, damaged or broken accidently.
If you find any errors in this manual or would like to make a comment, please do not hesitate to contact
me at: ea3gcy@gmail.com
THANK YOU for building the QPA-1 Amplifier kit.
Enjoy QRP!
73 Javier Solans, EA3GCY
QPA-1 Low level input QRP HF Amplifier and CW TX (3 a 30MHz) Page 10
SCHEMATIC
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