Elecraft KPA100UPKT User Manual
ELECRAFT KPA100 UPGRADE INSTRUCTIONS
Revision A, October 21, 2006
Copyright © 2006, Elecraft; All Rights Reserved
Introduction
The K2/100 transceiver 100-watt final output stage (KPA100 board) has undergone several important changes since it was
introduced. If your KPA100 was built according to any version of the Elecraft manual Appendix G, 100-W Stage and RS-323
I/O (K2/100), up through revision C, this kit will upgrade your older KPA100 board with all the changes to date. KPA100s
built according to revision D or later of the manual already incorporate these changes.
If you have not already done so, you must also install the shield upgrade (order KPA100SHDKT). You can install the shield
upgrade after you have completed the modifications described here.
Tools Required
You will need the following tools to install this modification kit:
Fine-tip temperature-controlled ESD-safe soldering station with 700 to 800F tip (370-430C). Recommend a spade
tip approx. 0.05” (1.3 mm) wide.Do not use a high-wattage iron or soldering gun since this can damage pads, traces,
or the parts themselves.
IC-grade solder, small-diameter (.031”or smaller, Kester #44 or equivalent).
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DO NOT use acid-core solder, water-soluble flux solder, additional flux or solvents of any kind. Use
of any of these will void your warranty.
A vacuum desoldering tool such as the Soldapullt® model DS017LS. Soldering braid is also handy for removing
excess solder in some situations. See, Soldering and Desoldering below for more information.
#2 Phillips screwdriver with a small handle.
Needle-nose pliers.
Small-point diagonal cutters. Flush-cutting type is required (Xcelite MS54-5J or equivalent).
Digital Multimeter (DMM) for voltage checks and confirming resistor values. A DMM with capacitance
measurement capability is desirable, but not required.
A magnifying glass or visor is often invaluable.
A conductive wrist strap and anti-static mat are strongly recommended. These items are available at very low cost
from Jameco, Mouser, and other electronics suppliers.
Refer to www.elecraft.com for tool sources and solder recommendations.
Soldering and Desoldering
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Use adequate ventilation when soldering; avoid inhaling smoke or fumes. Always wash your hands after
handling solder, as lead residue is highly toxic.
Removing components from double-sided boards can be difficult, since the holes are plated through to connect with traces on
both sides of the board. A number of suggestions are provided below.
When removing components:
Don't pull a lead or pin out of a hole unless the solder has been removed, or you are applying heat. Otherwise, you can
literally pull the cylindrical plating out of the plated-through hole that joins the top and bottom traces. If you’re having
difficulty, cut the component leads then remove the clipped lead from the hole. Only one component is reused (C83) and
it is clearly identified in the text.
Elecraft • www.elecraft.com • 831-662-8345
Limit soldering iron contact to a few seconds at a time.
Use a large vacuum desoldering tool (solder sucker) such as described under Tools Required above. Solder wick is
useful for removing excess solder from a joint, but requires great care if you use it to clean out a hole.
Invest in a PC board vice with a heavy base if possible. This makes parts removal easier because it frees up both hands.
If in doubt about a particular repair, ask for advice from Elecraft or from someone else with PCB repair experience.
Pre-Wound Toroids
Two new toroids are required for this upgrade. They are not difficult to wind, and full instructions are provided. If you prefer
not to wind them yourself, you can obtain a pre-wound toroids from an Elecraft-qualified source. Ordering information can
be found on our web site, www.elecraft.com. You do not need to send your cores or wire to the winding service.
Parts List
We recommend that you do a complete inventory before beginning assembly. The inventory helps you correctly identify all
the parts to avoid mistakes during assembly. The numbers or colors shown in parenthesis are those you should find on each
part. There may be other letters and numbers stamped on the parts as well.
Reference. Designator Description Qty
C64, C79 Capacitor, .0047 µF 5% 250V or greater, LS 0.4 2 E530262
C67, C86 Capacitor, 0047 µF, 100V, LS 0.2 2 E530102
L16, RFC1 Toroid Core, T50-1 (blue) 2 E680001
R4 Resistor, 100k (brn-blk-yel) 1/2W 1 E500006
R19, R20 Resistor, 1.6 ohm (1.6 Ω) 2W 2 E500130
R22 Resistor, 300 ohms (300Ω) 2W 1 E500129
R33 Resistor, 1K (brn-blk-red) 1/2W 1 E500013
R38, R39 Resistor, 22 ohm (22 Ω) 3 W 2 E500128
R40 Resistor, 22k (red-red-org) 1 E500090
RFC4, RFC5 RF Choke, 15 µH (brn-grn-blk) 2 E690006
Misc. #26 Red Enamel Wire 6ft E760002
Misc. #20 Solid Black Insulated Wire 5in E760006
Misc. Thermal pad (for Q1 and Q2) 2 E980051
Misc. Jack screw, Hex, 4-40, M/F 2 E700078
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The following procedures require you to remove components from the KPA100 printed-circuit board (PCB).
Part
Number
We strongly recommend you use the tools listed under Tools Required and follow the procedures carefully to avoid
damage to the PCB. See the hints under Soldering and Desoldering.
Part I: Removing the KPA100 Board
Disconnect all wires connecting your K2/100 to external devices.
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Set aside in a safe place all hardware you remove in the following steps for reinstallation later.
Remove the six screws that attach the KPA100 to the K2: there are two at the top front corners, one on each side of the
K2, and two at the rear.
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Lift the KPA100 up slightly to access the cable connections along the right side. Unplug the ribbon connector that
Standoff
attaches to the control board, the speaker, Aux 12V, and Aux RF connectors that attach to the K2 RF board. Lift the KPA100
off of the K2 and set it top down on a clean surface to avoid scratching the heat sink. Set the K2 aside in a safe place.
Remove the seven screws attaching the shield to the hex standoffs, lift the shield off and set it aside.
If you have the shield modification kit installed, remove the corner screw at J2 holding the solder lugs that connect the
shell of J2 to the hex standoff and shield.
Remove the seven hex standoffs and lock washers that secure the board to the heat sink. Two of the standoffs are near
the center of the board (see Figure 1). Do not lose the lock washers.
1/2 inch
Standoff
Q3
Q4
Q2
Q1
1/2 inch
Figure 1. Removing the KPA100 PCB.
Remove the three screws that attach the KPA100 back panel to the heat sink.
De-solder the two speaker leads at the loudspeaker. Take care not to drop solder on the speaker cone or otherwise
damage it.
Remove the screws securing Q3 and Q4. These screws secure the transistors to the heat sink. Do not lose the lock
washers.
Remove the four screws that secure PA power transistors Q1 and Q2 to the heat sink. Do not lose the lock washers.
Gently lift the KPA100 PCB off of the heat sink. Set the heat sink aside in a safe, clean place. Take care not to damage
the two thermal pads for the transistors. These are small rectangular pads that should remain attached to the heat sink.
Carefully peel the thermal pads off of PA power transistors Q1 and Q2 so that the bottom of each transistor shows clean
metal. You have new thermal pads in the kit to use when reassembling the KPA100. However, the old pads can be reused if
you remove them without tearing or otherwise damaging them.
Remove capacitor C83 from the PCB. Do not damage it. C83 is a large 1000 pF silver mica mounted on the PCB near
the end of binocular core transformer T2. C83 is soldered to the board with two short leads that rest on top of the solder pads
at the end of T2. The leads do not pass through the board. You can remove it easily by removing any excess solder on the
pads, then heating one lead at a time while gently lifting that end of the capacitor. You’ll install it directly on the end of T2
later.
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Part II: Input and Feedback Circuit Changes
R19 - 1.6
R20 - 1.6
R23 - Jumper
C82 - Removed
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Depending upon the age of your KPA100, the following changes to the Input and Feedback circuits may have
already been incorporated. The changed parts and their new values are shown in Figure 2. Proceed directly to Part
III if these changes have been made. Otherwise follow the procedure below to make the changes.
R39 - 22 Ω
R38 - 22 Ω
L18 - Jumper
Figure 2. Input and Feedback Circuit Component Changes.
Remove capacitor C82 (near where the Aux RF coaxial cable attaches to the PCB). C82 will not be replaced.
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When replacing parts with new parts or jumpers, first remove the old part, then clear the solder pad holes of
all solder before installing the new part. (See Soldering and Desoldering on page 1 for more information.) Install the
new part, solder and trim the leads flush with the PCB.
Replace resistor R23 with a jumper (R23 is near the small binocular core transformers T1.) Make the jumper from a 1”
(25.4 mm) length of the #20 insulated wire. Remove insulation from each end to leave just slightly less than 1/2” (12 mm) of
insulation in the center of the wire. Bend the stripped ends of the wire to fit the solder pads for R23. Solder and trim the
excess leads flush with the PCB.
R22 - 300 Ω
Ω
Ω
Remove insulation from each end, leaving 1/4” (6 mm) of insulation at the center of the wire. Bend the stripped ends of the
wire to fit the solder pads for L18. Solder and trim the excess leads flush with the PCB.
Replace inductor L18 (near Q1) with a jumper. Make the jumper from a 3/4” (19mm) length of the #20 insulated wire.
Replace R22 with a 300 ohm (300 Ω) 2 watt resistor.
Replace R20 with a 1.6 ohm (1.6 Ω) 2 watt resistor..
Replace R19 with a 1.6 ohm (1.6 Ω) 2 watt resistor.
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