Ramsey Electronics Stereo Amplifier QAMP20 User Guide

20 MTR 20 WATT QRP  
LINEAR AMPLIFIER KIT  
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!  
 
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  
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  
RAMSEY ELECTRONICS, INC.  
590 Fishers Station Drive  
Victor, New York 14564  
Phone (585) 924-4560  
Fax (585) 924-4555  
QAMP20 • 3  
 
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 • 4  
 
PARTS LIST FOR THE QAMP20 QRP POWER AMPLIFIER  
CAPACITORS:  
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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:  
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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:  
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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:  
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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:  
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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  
 
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.  
ˆ 1. Install S1, PC mount pushbutton switch. Solder all 6 pins securely.  
ˆ 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.  
ˆ 3. Install J3, PC mount DC power jack.  
ˆ 4. Install relay K1. Notice that it installs only one way.  
ˆ 5. Install potentiometer R4. This pot allows adjustment of the bias to the  
power transistors.  
ˆ 6. Install C9, .01 µf disc capacitor (marked .01 or 103 or 10 nf).  
ˆ 7. Install Q5, 221334 PNP transistor, with the flat side oriented toward D2.  
ˆ 8. Install R6, 470 ohm resistor (yellow-violet-brown).  
ˆ 9. Install R10, 51 ohm resistor (green-brown-black).  
ˆ 10. Install R11, 2.2 K ohm resistor (red-red-red).  
ˆ 11. Install R12, 10 K ohm resistor (brown-black-orange).  
ˆ 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.  
ˆ 13. Install C10, .1 µf disc capacitor (marked .1 or 104).  
ˆ 14. Install R7, 100 K ohm resistor (brown-black-yellow).  
QAMP20 • 7  
 
ˆ 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.  
ˆ 16. Install diode D4, 1N4002 style black epoxy diode. Check positioning of  
the banded end.  
ˆ 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.  
ˆ 18. Install C13, .1 µf disc capacitor (marked .1 or 104).  
ˆ 19. Install L4, 10 µH inductor (green body with brown-black-black bands).  
ˆ 20. Install R3, 10 K ohm resistor (brown-black-orange).  
ˆ 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.  
ˆ 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.  
ˆ 23. Install R5, 1 K ohm resistor (brown-black-red).  
ˆ 24. Install R2, 6.8 K ohm resistor (blue-gray-red).  
ˆ 25. Install R1, 1 K ohm resistor (brown-black-red).  
ˆ 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.  
ˆ 27. Install R8, 270 ohm resistor (red-violet-brown).  
ˆ 28. Install C11, .001 µf disc capacitor (marked .001 or 102).  
ˆ 29. Install R9, another 270 ohm resistor (red-violet-brown).  
ˆ 30. Install C12, another .001 µf disc capacitor (marked .001 or 102).  
ˆ 31. Install C8, .1 µf disc capacitor (marked .1 or 104).  
QAMP20 • 8  
 
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.  
ˆ 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.  
ˆ 33. Install C1, 100 to 220 µf electrolytic capacitor. Be sure to observe  
correct polarity.  
ˆ 34. Install C4, 180 ρf disc capacitor (marked 180 or 181).  
ˆ 35. Install C5, 330 ρf disc capacitor (marked 330 or 331).  
ˆ 36. Install C6, another 330 ρf disc capacitor (marked 330 or 331).  
ˆ 37. Install C7, another 180 ρf disc capacitor (marked 180 or 181).  
ˆ 38. Install wire jumper, JMP1. Use a scrap piece of component lead wire.  
ˆ 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  
Transistor bend pix  
body.  
ˆ 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).  
QAMP20 • 9  
 
ˆ 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.  
ˆ 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!  
12 turns through center of core  
IMPORTANT:  
Loop the first winding  
around the front of the  
core as shown.  
ˆ 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.  
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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  
14 turns through center of core  
IMPORTANT:  
Loop the first winding  
around the front of the  
core as shown.  
QAMP20 • 10  
 
through the core, continuing on in the same direction as before. Tin  
each end with solder all the way up to the core body. This winding is  
the 2 turn center-tapped secondary of T2.  
ˆ 45. Winding T1: Locate the remaining larger 2-hole ferrite core. Cut off a  
10 inch length of the enameled magnet wire and thread the wire  
through the core 3 times, pulling each turn gently tight. That's 3 times  
through each hole resulting in 3 complete turns through the core.  
Again, the amount of wire cut for this task is the proper amount. If you  
have too little or too much, then you have not wound the core correctly.  
Tin each end with solder as before. Tin all the way up to the core body.  
ˆ 46. Cut off another length of wire, 9½ inches long. Wind 1 turn  
through the core, loop out 1 inch, twist together and run one more turn  
through the core. Continue on in the same direction as before. Tin each  
end with solder all the way up to the core body. This winding is the 2  
turn center-tapped primary of T1.  
ˆ 47. Locate the smaller transformer (T2) and install it snugly on the PC  
board.  
ˆ 48. Install the larger transformer (T1) into the indicated location on the PC  
board.  
ˆ 49. Install L1, a 12 turn toroid inductor wound previously. If desired, a small  
dab of hot melt glue, bathtub sealer, or caulk may be used to secure  
the toroids.  
QAMP20 • 11  
 
ˆ 50. Install L2, the 14 turn toroid inductor - you marked it special,  
remember?  
ˆ 51. Install L3, the remaining 12 turn toroid inductor.  
This completes the assembly of your QRP power amplifier. Now's a good time to  
give your masterpiece a good going over, being especially alert for any:  
bridged-over solder joints;  
misplaced components;  
transistors or diodes placed wrong;  
electrolytic capacitors installed wrong.  
INITIAL TESTS:  
To prepare your amplifier for testing you'll need the following:  
1. Multimeter capable of measuring voltage and current.  
2. 12 volt DC power source of at least 3 amp capacity.  
3. Suitable dummy load and resonant antenna.  
4. QRP transmitter with a power output in the ½ to 2 watt range,  
such as the Ramsey QRP-20.  
5. Proper cables to interface between the QRP transmitter and the  
QRP power amplifier.  
With the above all set up and handy, let's get testing!  
1. Rotate Bias pot R4 fully CCW.  
2. Connect a multimeter to TP1; set the meter to read up to 5 volts DC  
3. Connect a dummy load to J1, the amplifier RF output. In a pinch, a light bulb  
may be used - see the section, "Verifying RF Power Output."  
QAMP20 • 12  
 
4. Temporarily install a jumper from the collector of Q3 to ground.  
5. Apply power to the amplifier but do not turn on the transmitter. Measure  
the current drawn by the amplifier and slowly rotate the bias pot, R4,  
clockwise until you reach a reading of ¼ amp. Do not allow the current to  
rise above ½ amp. If you cannot adjust or reduce the current, disconnect  
the power supply and consult the troubleshooting hints section. The voltage  
at TP1 should be about 3.2 to 3.5 volts.  
6. Turn off power. Disconnect jumper from Q3 to ground.  
7. Connect the QRP transmitter to the input of the amplifier. Key the  
transmitter. You should hear the T-R relay click and see amplified power  
output. Measure the DC current draw; it should be in the 1 to 3 amp range  
depending upon power output. Unkey the transmitter. The relay should  
drop out and the current should drop back down to ¼ amp.  
This completes the testing of your QRP power amplifier. The PC board should  
be mounted into a protective enclosure to guard against accidental contact. The  
Ramsey CQAMP case set provides an ideal perfectly sized cabinet that  
matches all other Ramsey kits.  
Study the following sections on DC power supply and RF power considerations.  
Operate your transmitter with good amateur practice.  
YOUR POWER SUPPLY AND RF OUTPUT POWER  
For optimum performance, one or two volts of extra DC supply power can make  
quite a difference in any RF power amplifier. For example, two lantern batteries  
in series, or 8 D cells, will obviously provide about 12 volts with sufficient  
current capability for casual operating. For maximum RF output power, use a  
supply of 13 to 14 volts DC. The easiest method is to place two fresh D cells in  
series with your power source if a full 13.6 - 15 volts DC is not available. Be  
aware that batteries are not the optimum power source, especially if you are  
prone to long QSOs! A word of caution concerning wall plug style AC adapter  
power supplies: They are not suitable for operation of your amplifier due to their  
poor regulation, AC ripple content, and RFI susceptibility.  
With 1 watt of drive and a supply voltage in the 11-12 volt range, you can  
expect a 1 to 2 amp current draw and about 10 watts of RF output power. With  
a solid 13 to 14 volt supply, you can expect about 2 to 3 amps current draw and  
up to 10 or 12 watts of RF output power. With 2 watts of RF drive, expect up to  
20 watts RF output!  
VERIFYING TRANSMITTER RF OUTPUT  
The most important thing to know is whether your transmitter is delivering some  
measurable and reassuring level of RF power. Then you can continue on to  
adding the QRP amplifier and checking out the whole set-up.  
QAMP20 • 13  
 
Ideally, you have a small RF wattmeter, already inserted in the antenna line,  
capable of accurately measuring low output power in watts. And it cost you less  
than what you paid for the transmitter kit. Right? In the words of Wayne from  
"Wayne's World"... Not! So here are a few other ideas for you to try.  
Saying the same thing another way, we assume you know that accurate,  
commercially built RF wattmeters cost much more than what you paid for this  
Ramsey amplifier kit. Since this solid-state amplifier does not require lots of  
critical tuning or adjustments, a periodic power output check-up should suffice. If  
you don’t own or have access to a low-level RF power meter, use a trick that is  
decades old - the common flashlight or panel bulb. All you need to know is the  
basic difference between bright, superbright, dim, unlit and burned out! Using a  
light bulb to check power output is also a satisfying way to put Ohm's Law to  
work. Your Radio Shack catalog specifies operating voltage and current in  
milliamperes for a variety of small replacement lamps and a local automobile  
parts store is a treasure trove of various other lamps. It may be worth your while  
to make up a simple plug-in "output tester" for your amplifier - a male RCA plug  
connected to a socket for the bulb of your choice or even soldered directly to the  
bulb.  
RF voltage levels in this amplifier can vary from 2 to 25 volts RMS depending on  
various factors. Typically, 1 watt power levels are achieved in the 5 to 7 volts  
RMS range, 5 watts at 12 to 15 volts, and 10 watts at 20 to 25 volts. A good test  
bulb for this amplifier is the #93 automobile lamp bulb or the #1156 type bulb.  
Both are 12.8 volt rated, with the #93 being specified at 1 amp and the #1156  
being 2 amps for normal brilliance. Using some Ohm's law calculations shows  
that the #93 is a 12 watt lamp and the #1156 is a 24 watt lamp. We can  
conclude that 10 watts or so of RF should light a #93 bulb reasonably well, while  
20 watts should be about right for a #1156. Try it out!  
Please remember, though, that a flashlight bulb does NOT present the proper  
load impedance to the amplifier output, so theoretical calculations based on the  
bulb`s rating can only be approximate. For example, the #93 at full brilliance  
presents a 12 ohm load to the amplifier. Because of this, the amplifier may act  
"flakey" when tuning up into a light bulb, and by all means you should not  
consider a light bulb an accurate indicator of the QAMP-20's performance! If  
ANY light bulb lights up when connected to the antenna jack of this amplifier,  
you can be satisfied that you have RF output power at least equal to the DC  
power rating of the bulb you are using. If you burn out your bulb, rejoice and put  
your rig on the air!  
Amateur radio magazines and handbooks provide a variety of circuits for RF  
wattmeters and relative field-strength indicators, including methods of using your  
VOM as an indicating device. CQ magazine for March 1990 offers an article by  
 
KB4ZGC on how to make a highly accurate yet inexpensive dummy load and  
wattmeter capable of showing 1/10-watt differences in RF power. If you use a  
wattmeter characterized for the HF frequency region, it will not give accurate  
results at the much higher two meter frequencies, although it will be quite  
adequate for go/no-go testing.  
MAXIMIZING RF POWER OUTPUT  
The simplest way to ensure maximum reasonable power output without  
component damage is to run the DC voltage in the 13 to 14 volt range,  
observing a maximum limit of +15VDC. Typically, an automobile power source  
is 13.6 volts when the engine is running, and most mobile rigs are specified at  
this voltage level.  
IMPORTANT NOTE: If you are experimenting with this transmitter and see a  
sudden and massive increase in power output and DC current, you have not  
reached the promised land or created a 100 watt amplifier! Sudden surges like  
that are a sure sign of amplifier self-oscillation. Kill the DC power supply  
immediately because your RF power transistors are heading to self-destruction  
while probably interfering with every TV set in the neighborhood! A poorly  
matched antenna along with higher supply voltages is usually responsible for  
this occurring. Any prolonged "parasitic" emissions may also overheat and  
destroy other components in the amplifier.  
TROUBLESHOOTING HINTS  
The QRP power amplifier is very straight forward and simple to troubleshoot.  
When beginning to track down a problem, use some common sense to narrow  
down your search area.  
If the amplifier is not keying upon application of RF power, check to see if the T-  
R relay circuitry is operating. A quick read-over of the theory of operation tells  
us the diode detector senses the RF and a pair of transistors amplifies the  
signal to activate the T-R relay. Proper logic tells us to: 1) First check and see if  
RF is getting to the diodes; 2) see if they are detecting RF; 3) see if the  
transistors are driving the relay. Proper procedure is to take just one part of the  
circuit at a time and follow the signal through.  
If the amplifier does not amplify, check to see if RF is flowing through to  
transformer T2 and across to the RF power transistors. Amplified output should  
appear at output transformer T1 and then on to the low pass filter. Remember  
that RF enters and exits through relay contacts on K1.  
Do the transistors get too hot? Do they get hot without amplifying? Things to  
check are the bias circuitry and RF path through the relay. The amplifier should  
draw about ¼ amp with no signal applied. If you see more than that, recheck  
the bias setting (see the section "INITIAL TESTS").  
QAMP20 • 15  
 
If you hear an AC hum on the transmitted signal, usual causes are RF getting  
back into the power supply or a bad VSWR on the antenna.  
These short checks in no way detail any and all problems that can rear their  
ugly head, but should get you on the way to solving most errors. We'd like to be  
able to foresee a problem a builder may encounter, but the sheer number of  
parts and the permutations and combinations of installing them makes any list  
of precise, exact solutions impossible. If you run into a roadblock, gather all your  
thoughts and information and give a call to the factory for some help. If you elect  
to enlist the help of a local expert, great...but be sure the expert is qualified (no  
need for having someone lead you down the wrong path)! Remember: You may  
always return the kit for factory service, and there's no charge if the problem is  
our fault. See the warranty on the last page of this manual.  
USING THE QRP POWER AMPLIFIER  
Hooking up and using the amplifier is easy: Just connect your existing  
transmitter to the QAMP input and the antenna to the QAMP output. A resonant  
antenna is an absolute requirement for QRP operation, and an amplifier is not a  
"band-aid" for a poor antenna system!  
For maximum performance, a QRP station must include the following:  
1
2
3
A resonant antenna (dipole or quarter-wave vertical);  
Good quality coaxial feedline and connectors;  
An effective earth ground.  
We cannot expect good results from low levels of RF output if the power gets  
wasted in lousy coax, corroded connections, or poor antennas.  
If you elect to use an antenna tuner, it is extremely important that you  
understand exactly how to use tuners and what they can and cannot do. A few  
watts of RF can easily become lost in an incorrectly adjusted antenna matching  
device. The whole idea of a QRP station is to keep things simple and  
economical, so we cannot overemphasize the priority of a clean, efficient  
connection of the amplifier output to a resonant antenna.  
ENCLOSURE RECOMMENDATIONS  
Your finished amplifier can be installed in a variety of enclosures of your own  
design and choosing. You might be planning to combine several Ramsey circuit  
kit boards in a single enclosure. Use of the inexpensive and attractive Ramsey  
case and hardware set will give your unit that nice finished look and increase its  
resale value. These sturdy black instrument cases are supplied with neatly  
lettered front and rear panels, switch knobs, rubber feet and mounting screws.  
QAMP20 • 16  
 
While we believe that the Ramsey enclosure and knob option is a fine value for  
finishing off your Ramsey kit, we are happy to give you a couple of additional  
suggestions and our reasons for them. If your first goal is economy and rugged  
portability, you will find that the circuit board can be mounted nicely in a  
standard VHS videotape storage box, which also gives room for storing cables,  
a small homemade keyer, etc. The controls are easily mounted at one end of  
such a box. It may be necessary to cut away the molded posts which secure  
the tape itself. These storage boxes come in several styles, so pick one which  
truly looks practical as a project enclosure. To accomplish RF shielding, the  
most economical metal enclosure nicely suited for Ramsey amateur kit board is  
Radio Shack No. 270-253A. This metal utility cabinet can accommodate both a  
receiver, transmitter and amplifier board, plus speaker, with room for various  
refinements you might like to add.  
PARTS LAYOUT QAMP20 POWER AMPLIFIER KIT  
QAMP20 • 17  
 
QAMP20 • 18  
 
The Ramsey Kit Warranty  
Please read carefully BEFORE calling or writing in about your kit. Most  
problems can be solved without contacting the factory.  
Notice that this is not a "fine print" warranty. We want you to understand your rights and ours too! All  
Ramsey kits will work if assembled properly. The very fact that your kit includes this new manual is your  
assurance that a team of knowledgeable people have field-tested several "copies" of this kit straight from  
the Ramsey Inventory. If you need help, please read through your manual carefully, all information  
required to properly build and test your kit is contained within the pages!  
1. DEFECTIVE PARTS: It's always easy to blame a part for a problem in your kit, Before you conclude  
that a part may be bad, thoroughly check your work. Today's semiconductors and passive components  
have reached incredibly high reliability levels, and it’s sad to say that our human construction skills have  
not! But on rare occasions a sour component can slip through. All our kit parts carry the Ramsey  
Electronics Warranty that they are free from defects for a full ninety (90) days from the date of purchase.  
Defective parts will be replaced promptly at our expense. If you suspect any part to be defective, please  
mail it to our factory for testing and replacement. Please send only the defective part(s), not the entire kit.  
The part(s) MUST be returned to us in suitable condition for testing. Please be aware that testing can  
usually determine if the part was truly defective or damaged by assembly or usage. Don't be afraid of  
telling us that you 'blew-it', we're all human and in most cases, replacement parts are very reasonably  
priced.  
2. MISSING PARTS: Before assuming a part value is incorrect, check the parts listing carefully to see if it  
is a critical value such as a specific coil or IC, or whether a RANGE of values is suitable (such as "100 to  
500 uF"). Often times, common sense will solve a mysterious missing part problem. If you're missing five  
10K ohm resistors and received five extra 1K resistors, you can pretty much be assured that the '1K ohm'  
resistors are actually the 'missing' 10 K parts ("Hum-m-m, I guess the 'red' band really does look orange!")  
Ramsey Electronics project kits are packed with pride in the USA. If you believe we packed an incorrect  
part or omitted a part clearly indicated in your assembly manual as supplied with the basic kit by Ramsey,  
please write or call us with information on the part you need and proof of kit purchase.  
3. FACTORY REPAIR OF ASSEMBLED KITS:  
To qualify for Ramsey Electronics factory repair, kits MUST:  
1. NOT be assembled with acid core solder or flux.  
2. NOT be modified in any manner.  
3. BE returned in fully-assembled form, not partially assembled.  
4. BE accompanied by the proper repair fee. No repair will be undertaken until we have received the  
MINIMUM repair fee (1/2 hour labor) of $25.00, or authorization to charge it to your credit card account.  
5. INCLUDE a description of the problem and legible return address. DO NOT send a separate letter;  
include all correspondence with the unit. Please do not include your own hardware such as non-Ramsey  
cabinets, knobs, cables, external battery packs and the like. Ramsey Electronics, Inc., reserves the right  
to refuse repair on ANY item in which we find excessive problems or damage due to construction  
methods. To assist customers in such situations, Ramsey Electronics, Inc., reserves the right to solve  
their needs on a case-by-case basis.  
The repair is $50.00 per hour, regardless of the cost of the kit. Please understand that our technicians are  
not volunteers and that set-up, testing, diagnosis, repair and repacking and paperwork can take nearly an  
hour of paid employee time on even a simple kit. Of course, if we find that a part was defective in  
manufacture, there will be no charge to repair your kit (But please realize that our technicians know the  
difference between a defective part and parts burned out or damaged through improper use or assembly).  
4. REFUNDS: You are given ten (10) days to examine our products. If you are not satisfied, you may  
return your unassembled kit with all the parts and instructions and proof of purchase to the factory for a  
full refund. The return package should be packed securely. Insurance is recommended. Please do not  
cause needless delays; read all information carefully.  
QAMP20 • 19  
 
QAMP20 20 WATT LINEAR AMPLIFIER  
Quick Reference Page Guide  
How it works...................................4  
Parts list..........................................5  
Learn as you Build..........................6  
QAMP20 assembly instructions .....7  
Initial testing ..... ...........................12  
Verifying RF output power............13  
Using the QAMP20.......................16  
Parts layout diagram ....................17  
Schematic diagram.......................18  
Ramsey kit warranty.....................19  
REQUIRED TOOLS  
TOTAL SOLDER POINTS  
Soldering Iron Ramsey WLC100  
Thin Rosin Core Solder Ramsey RTS12  
121  
ESTIMATED ASSEMBLY  
TIME  
Beginner...............4 hrs  
Intermediate .........2 hrs  
Advanced .............1.5 hrs  
Needle Nose Pliers  
RTS05  
Ramsey MPP4 or  
Small Diagonal Cutters Ramsey RTS04  
<OR> Technician’s Tool Kit TK405  
ADDITIONAL SUGGESTED ITEMS  
Holder for PC Board/Parts Ramsey HH3  
Desoldering Braid Ramsey RTS08  
Digital Multimeter Ramsey M133  
Price: $5.00  
Ramsey Publication No. MQAMP20  
Assembly and Instruction manual for:  
RAMSEY MODEL NO. QAMP20 20 METER 20 WATT  
LINEAR AMPLIFIER KIT  
RAMSEY ELECTRONICS, INC.  
590 Fishers Station Drive  
Victor, New York 14564  
This Quality Electronics  
Kit was designed and  
packed in the USA  
Phone  
Fax  
(585) 924-4560  
(585) 924-4555  
 

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