Ramsey Electronics QAMP20 User guide

QAMP20 • 1
Ramsey Electronics Model No. QAMP20
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!
20 MTR 20 WATT QRP
LINEAR AMPLIFIER KIT
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QAMP20 • 2
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
Ramsey Electronics publication No. MQAMP20 Revision 1.5a
First printing: January 1993
COPYRIGHT 1994 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Victor, New York
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.

QAMP20 • 3
Ramsey Publication No. MQAMP20
Price $5.00
TABLE OF CONTENTS
Introduction to the QAMP20........... 4
How it works................................... 4
Parts list ......................................... 5
Learn as you Build ......................... 6
QAMP20 assembly instructions ..... 7
Initial tests ..... .............................. 12
Verifying RF output power ........... 13
Troubleshooting tips..................... 15
Using the QAMP20 ...................... 16
Parts layout diagram .................... 17
Schematic diagram ...................... 18
Ramsey kit warranty .................... 19
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
RAMSEY ELECTRONICS, INC.
590 Fishers Station Drive
Victor, New York 14564
Phone [phone]
Fax [phone]
www.ramseykits.com
20 METER QRP
CW POWER
AMPLIFIER KIT

QAMP20 • 4
INTRODUCTION
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 • 5
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]
RESISTORS:
3 1 K ohm resistors (brown-black-red) [R1,5, TP1]
1 6.8 K ohm resistor (blue-gray-red) [R2]
2 10 K ohm resistors (brown-black-orange) [R3,12]
1 470 ohm resistor (yellow-violet-brown) [R6]
1 100 K ohm resistor (brown-black-yellow) [R7]
2 270 ohm resistors (red-violet-brown) [R8,9]
1 51 ohm resistor (green- brown-black) [R10]
1 2.2 K ohm resistor (red-red-red) [R11]
1 5 K potentiometer (marked 502M) [R4]
SEMICONDUCTOR DEVICES:
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 • 6
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 • 7
In all the following instruction steps, our word "INSTALL" means to do the
following:
•Insert the part, oriented correctly, into its correct holes in the PC board.
•If helpful, gently bend the part’s wire leads or tabs to hold it in place, with the
body of the part snugly against the top side (component side) of the PC
board.
•Solder all wires or pins of the part, whether the 2 wires of a resistor or the 3
or 4 wires of a transistor.
•Trim all excess wires extending beyond each solder connection, taking care
that wire trimmings do not become lodged in PC board solder connections.
CONSTRUCTION:
Since you may appreciate some "warm-up" soldering practice as well as a
chance to put some "landmarks" on the PC board, we'll first install some
"hardware" components.
1. Install S1, PC mount pushbutton switch. Solder all 6 pins securely.
2. Install J1and J2, PC mount RCA phono jacks. Solder all 4 pins on each
securely as these connectors will be subjected to some stress when
coax cables are connected to them.
3. Install J3, PC mount DC power jack.
4. Install relay K1. Notice that it installs only one way.
5. Install potentiometer R4. This pot allows adjustment of the bias to the
power transistors.
6. Install C9, .01 µf disc capacitor (marked .01 or 103 or 10 nf).
7. Install Q5, 221334 PNP transistor, with the flat side oriented toward D2.
8. Install R6, 470 ohm resistor (yellow-violet-brown).
9. Install R10, 51 ohm resistor (green-brown-black).
10. Install R11, 2.2 K ohm resistor (red-red-red).
11. Install R12, 10 K ohm resistor (brown-black-orange).
12. Install D2 and D3, 1N4148 style signal diodes (glass body with black
band). Pay special attention to the banded ends. The banded end on a
diode is the cathode and must be oriented correctly or the circuit will
not work. Both diode D3 and diode D2 are detectors for sensing applied
RF power.
13. Install C10, .1 µf disc capacitor (marked .1 or 104).
14. Install R7, 100 K ohm resistor (brown-black-yellow).

QAMP20 • 8
15. Install Q3 and Q4, 2N3904 NPN transistors, observing proper
orientation of the flat side. These two transistors amplify the signal
diode's output to a level high enough to close relay K1.
16. Install diode D4, 1N4002 style black epoxy diode. Check positioning of
the banded end.
17. Install jumper JMP2. Use a piece of scrap component lead wire bent
into a "staple" shape and inserted into the board like a component.
Jumpers act as electronic "bridges" carrying signals over PC board
circuit traces underneath.
18. Install C13, .1 µf disc capacitor (marked .1 or 104).
19. Install L4, 10 µH inductor (green body with brown-black-black bands).
20. Install R3, 10 K ohm resistor (brown-black-orange).
21. Install C2, 10 µf electrolytic capacitor. Electrolytic capacitors are
polarized with a ( + ) and a ( - ) lead and must be installed correctly for
proper operation. Generally, capacitors have their ( - ) lead marked
with a black stripe while PC boards have the ( + ) hole indicated.
22. Install D1, 6.2 volt Zener diode (gray body with a black band). This
diode provides a stable voltage which is used to provide bias for the
power transistors.
23. Install R5, 1 K ohm resistor (brown-black-red).
24. Install R2, 6.8 K ohm resistor (blue-gray-red).
25. Install R1, 1 K ohm resistor (brown-black-red).
26. Locate another 1 K ohm resistor (brown-black-red). Trim back one lead
to a length of ¼ inch. Bend this wire into a small loop as shown. This
loop will act as a convenient point to connect a test probe for setting
the bias voltage. Insert the resistor into the PC board and hold it
carefully while you solder it to the board.
27. Install R8, 270 ohm resistor (red-violet-brown).
28. Install C11, .001 µf disc capacitor (marked .001 or 102).
29. Install R9, another 270 ohm resistor (red-violet-brown).
30. Install C12, another .001 µf disc capacitor (marked .001 or 102).
31. Install C8, .1 µf disc capacitor (marked .1 or 104).

QAMP20 • 9
These last four parts (R8,9 and C11,12) form parasitic suppression networks
across each transistor to suppress any tendency for high frequency oscillation
in the power amplifier.
32. Install C3, another .1 µf disc capacitor (marked .1 or 104). Both of
these capacitors bypass the center tap of the ferrite transformers to
ground. Bypass means to provide a low impedance path to ground.
33. Install C1, 100 to 220 µf electrolytic capacitor. Be sure to observe
correct polarity.
34. Install C4, 180 ρf disc capacitor (marked 180 or 181).
35. Install C5, 330 ρf disc capacitor (marked 330 or 331).
36. Install C6, another 330 ρf disc capacitor (marked 330 or 331).
37. Install C7, another 180 ρf disc capacitor (marked 180 or 181).
38. Install wire jumper, JMP1. Use a scrap piece of component lead wire.
39. Locate the MOSFET power
transistors and prepare the leads for
insertion into the PC board. Bend
down the two outside leads about
1/8" from the transistor body and the
center lead about 3/16" from the
body.
40. Mount the transistors and heatsinks to the PC board using the 4-40
screws and nuts. Solder all transistor leads. Note that the heatsinks
may look slightly different from the ones shown.
We're almost finished. All we need to do now is install a few remaining parts
that have to be handmade - for that "old-world craftsmanship" touch! We'll
prepare all those parts now for further assembly. We supplied plenty of
enameled wire for your kit but if you mess up, you can get a whole 50' spool of
it from Radio Shack (278-1341).
Transistor bend pix

QAMP20 • 10
41. Winding L1 and L3 toroid RF coils (two identical units ): Locate 2 of the
donut shaped yellow toroid cores provided in the kit. Cut 8" of the
enameled magnet wire and, following the drawing, thread the wire
through the core 12 times - not 11, not 13; it MUST be 12 times
through the core, pulling each turn gently tight. Winding too tightly
runs the risk of scraping off the enamel insulation and shorting the
wire. Tin each end with solder by holding your soldering iron and solder
the ends until the insulation melts away and the copper wire
underneath coats nicely with solder. Tin all the way up to the toroid
core body.
42. Winding L2: Locate the remaining yellow toroid core and cut 9½" of
enameled magnet wire. Wind 14 turns through the core using the same
procedure as above. Tin the wire ends as before. Mark this part with a
piece of tape, a dab of paint or a magic marker. We don't want to
confuse it with the other two toroid coils wound just before!
43. Winding T2: Locate the smaller of the two 2-hole ferrite cores. Cut off
one 11 inch length of enameled magnet wire and thread the wire
through the core 6 times, pulling each turn gently tight. That's 6 times
through each hole, resulting in 6 complete turns through the core.
Be especially careful not to strip the insulation by pulling too tightly
around the core. The amount of wire cut for this task is the proper
amount. If you have too little or too much, you haven’t wound the core
correctly. Tin each end with solder as before. Tin all the way up to the
core body. This winding is the primary of transformer T2.
44. Cut off another length of the same wire, 8 inches long. Wind 1 turn
through the core, loop out 1 inch, twist together and run one more turn
12 turns through center of core
IMPORTANT:
Loop the first winding
around the front of the
core as shown.
IMPORTANT:
around the front of the
core as shown.
Loop the first winding
14 turns through center of core