Need a little extra boost for your QRP rig? Believe it or not, 20 watts is only
about an ‘S’ unit below a 100 watt rig! This nifty little amp will add some
“punch” to any QRP transmitter.
•Works great with Ramsey QRP rigs or any other 1-2 watt
transmitters
•Built-in T/R relay automatically switches between receive and
transmit
•Runs on 12 volts DC at 2 to 4 amps; ideal for field day or battery
operation
•Multistage low pass filter for a clean signal
•Operates all modes: CW, SSB, or AM
•Fast, easy, and fun 2 hour assembly
•Informative manual answers questions on theory, hook-ups, and
uses - enhances resale value too!
•Clear, concise assembly instructions carefully guide you to a
finished kit that works the FIRST time!
QAMP20 • 1
RAMSEY TRANSMITTER KITS
• FM10A, FM25B FM Stereo Transmitters
• TV6 Television Transmitter
• Cube TV Transmitters
RAMSEY RECEIVER KITS
• FR1 FM Broadcast Receiver
• AR1 Aircraft Band Receiver
• SR2 Shortwave Receiver
• AA7 Active Antenna
• SC1 Shortwave Converter
RAMSEY HOBBY KITS
• SG7 Personal Speed Radar
• SS70A Speech Scrambler
• TT1 Telephone Recorder
• SP1 Speakerphone
• MD3 Microwave Motion Detector
• PH10 Peak hold Meter
• LC1 Inductance-Capacitance Meter
RAMSEY AMATEUR RADIO KITS
• DDF1 Doppler Direction Finder
• HR Series HF All Mode Receivers
• QRP Series HF CW Transmitters
• CW7 CW Keyer
• CPO3 Code Practice Oscillator
• QRP Power Amplifiers
RAMSEY MINI-KITS
Many other kits are available for hobby, school, Scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.
QAMP20 QRP CW POWER AMPLIFIER KIT INSTRUCTION MANUAL
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.
1994 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
QAMP20 • 2
Ramsey Publication No. MQAMP20
Price $5.00
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
20 METER QRP
CW POWER
AMPLIFIER KIT
TABLE OF CONTENTS
Introduction to the QAMP20 ........... 4
How it works ................................... 4
Parts list ......................................... 5
The Ramsey QAMP series of QRP power amplifiers are compact 10 to 20
watt RF amplifiers for QRP CW transmitters. These amplifiers are made to
be driven by transmitters in the ½ to 2 watt range. Built-in to the power
amplifier is a sensitive T-R relay which will switch the unit in and out of the
antenna line. When in receive, the amplifier is bypassed and the antenna
feeds directly to the input jack. When you go to transmit, the T-R circuit
detects the transmit RF power and automatically switches the power
amplifier into the circuit and amplifies the applied RF power. If you decide to
run "barefoot", turning off the QAMP will disable the amplifier and your QRP
transmitter will feed directly through the amplifier without any amplification.
Power is supplied by any 12 to 15 volt DC source with a current draw of 1 to
3 amps depending upon RF power output. A 5 pole low pass filter using
toroid cores keeps harmonics and spurious signals very low. The entire
amplifier is very easy to construct, but does require you to wind a few coils
and RF transformers - we'll lead you step-by-step through all steps!
HOW IT WORKS
The QRP amplifier is very simple with most of the "magic" being done by just
a few parts, the pair of MOSFET transistors and the ferrite wideband
transformers. Transformer T2 matches the 50 ohm amplifier input to the
push-pull inputs of the FET transistors. The term push-pull means that one
transistor amplifies the positive portion of the input signal while the other
transistor amplifier the negative portion - put another way, one is pushing
while the other is pulling! The center tapped transformer splits the input
signal so each transistor will only amplify the correct part of the input signal.
Incidentally, this push-pull technique has been used for years in both
vacuum tube and solid-state gear.
The push-pull signal output from the FETs is combined and impedance
matched to 50 ohms by ferrite transformer T1. To reduce any harmonic
content, a 5 pole low pass filter consisting of L1,2,3 and C4,5,6,7 is used.
The FET transistors are biased "on" slightly for best gain and linearity. Zener
diode D1 provides a constant voltage for the bias network R2,3,4. Bias pot
R4 allows adjustment of bias voltage to the FET transistor gates. It is
adjusted for a set amount of current through the transistors.
The T-R relay circuit uses a simple diode detector consisting of D2 and D3.
The detector output is amplified by transistors Q3 and Q4 to drive relay K1.
QAMP20 • 4
PARTS LIST FOR THE QAMP20 QRP POWER AMPLIFIER
CAPACITORS:
1 100 to 220 µf electrolytic capacitor [C1]
1 10 µf electrolytic capacitor [C2]
4 .1 µf disc capacitors (marked .1 or 104) [C3,8,10,13]
2 180 ρf disc capacitors (marked 180 or 181) [C4,7]
2 330 ρf disc capacitors (marked 330 or 331) [C5,6]
2 .001 µf disc capacitors (marked .001 or 102 or 1000) [C11,12]
1 .01 µf disc capacitor (marked .01 or 103 or 10 nf) [C9]
1 Zener diode, 6.2 volt (gray body with black band) [D1]
2 1N4148 type signal diodes (glass body with black band) [D2,3]
1 1N4002 style black epoxy diode [D4]
2 Power MOSFET transistors (marked P16NF06) [Q1,2]
2 2N3904 NPN transistors [Q3,4]
1 221334 PNP transistor [Q5]
OTHER COMPONENTS:
1 Relay DPDT 12 volt [K1]
1 PC mount pushbutton switch [S1]
2 RCA style PC mount phono jacks [J1,2]
1 2.5 mm DC power jack [J3]
2 Heatsink [HS1,2]
3 Yellow toroid coil core [L1,2,3]
1 10 µH inductor [L4]
1 2 hole small ferrite transformer core [T2]
1 2 hole large ferrite transformer core [T1]
7' #24 enameled magnet wire (thin wire) [for winding L1,2,3 and T1,2]
2 4-40 x ¼” machine screw
2 4-40 hex nut
QAMP20 • 5
REQUIRED, NOT SUPPLIED:
Ramsey case, knob and panel set, Ramsey part no. CQRP
Matching input and output cables to existing QRP transmitter
12 volt DC power supply 3 amp rating
Proper dummy load or resonant antenna
"THE RAMSEY LEARN-AS-YOU-BUILD ASSEMBLY STRATEGY"
Take a look at the parts layout diagram. There is quite a lot to the construction
of the QAMP20. It's easier than it seems once you get going, especially after
you have installed a few of the "landmark" components. Once these "landmark"
components are placed, other parts’ positions are referenced to them, and
construction goes quite smoothly. This will help in relating from one part to
another what specific holes it may require on the board, and that part's
orientation. In addition, we will discuss the purpose of most components or
groups of components as we go along. This is the Ramsey Learn-As-You-Build
kit assembly philosophy. Be sure to read through all the steps, and check the
boxes as you go to be sure you didn't miss any important steps. Most of the
problems we find here at the factory are due to faulty assembly, no matter how
experienced the builder may be: it’s especially tough to tell a 30 year
experienced ham that he goofed! Before you run the circuit, check all diodes
and polarized capacitors for proper orientation.
TIPS AND NOTES:
Use a good soldering technique - let your soldering iron tip gently heat the
traces to which you are soldering. Heat both wires and pads simultaneously.
Apply the solder on the iron, lead, and the pad when pad and wire is hot enough
to melt the solder. The actual joint should look like a drop of water on paper
(somewhat soaked in).
Parts are mounted on the top side of the board. This is the side that has no
traces or pads on it.
Part orientation
- All parts in this kit are mounted at 90 degree angles, meaning
parts are either parallel or perpendicular to the sides of the board.
Part installation
- When parts are installed, the part is placed flat to the board,
and the leads are bent on the backside of the board to prevent the part from
falling out before soldering. The part is then soldered into place, and the spare
leads are removed. Make sure lead lengths are as short as possible when
dealing with the RF section of this kit.
QAMP20 • 6
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