MFJ Enterprises Versa-Tuner II User manual

INSTRUCTION MANUAL
CAUTION: Read All Instructions Before Operating Equipment
MFJ ENTERPRISES, INC.
300 Industrial Park Road
Starkville, MS 39759 USA
Tel: [phone] Fax: [phone]
COPYRIGHT 2013 MFJ ENTERPRISES, INC.
C
Model MFJ-941EK
VERSION 1A

DISCLAIMER
Information in this manual is designed for user purposes only and is not
intended to supersede information contained in customer regulations, technical
manuals/documents, positional handbooks, or other official publications. The
copy of this manual provided to the customer will not be updated to reflect
current data.
Customers using this manual should report errors or omissions,
recommendations for improvements, or other comments to MFJ Enterprises, 300
Industrial Park Road, Starkville, MS 39759. Phone: [phone]; FAX: (662)
323-6551. Business hours: M-F 8-4:30 CST.

MFJ-941EK Tuner Kit Instruction Manual
- 2 -
INTRODUCTION
General Information:
This manual contains all the information you'll need to build, calibrate, and use
your new MFJ-941EK Versa-Tuner II kit. The Versa-Tuner II is actually four very
useful station accessories combined into one package. The first is MFJ's wide-
range 300-Watt T-network that can match virtually any HF antenna you're likely to
encounter. The second is our highly accurate dual-range SWR/Wattmeter that
features cross-needle metering. The third is an eight-position RF-routing switch
for selecting a variety of antennas, either through the tuner or around the tuner in
bypass mode. And, finally, there's a built-in 300-Watt 4:1 balun to accommodate
antennas using balanced feedline. Despite its versatility, the circuitry and
mechanical layout for the MFJ-941EK are straight forward, and these instructions
will guide you through assembly from start to finish.
Before You Start:
Prepare a clean work surface and use muffin tins, egg cartons, or small paper
cups to organize your parts. To reduce eyestrain, choose an area with strong
overhead lighting and add a high-intensity desk lamp for close-up work.
Construction requires the tools listed below:
[ ] Soldering iron with a narrow chisel tip.
[ ] Soldering-iron holder with a moistened cleaning sponge.
[ ] Your choice of leaded or lead-free solder with rosin or no-clean flux.
[ ] Small needle-nose pliers or surgical hemostat.
[ ] Side-cutter type wire nippers.
[ ] Solder sucker or de-soldering braid
[ ] Magnifying glass or loupe for reading component markings
[ ] Phillips-head screwdriver
[ ] 5/64" Allen wrench (for knobs)
[ ] 3/32" Allen wrench (for shaft coupler)
[ ] 1/4" nut driver (for 4-40 hardware)
[ ] 5/16" nut driver (for 6-32 hardware)
[ ] 3/8" nut driver (for 10-32 hardware)
[ ] 7/16" nut driver (for insulated terminal posts)
[ ] 1/2" nut driver (for 3/8" ID control-nuts)
As you work, watch for the four most common kit-building errors:
1. Wrong Part: Identify, sort, and organize all parts ahead of time.
2. Reversed Polarity: Double check diode and meter polarity.
3. Defective Soldering: Routinely check for cold solder joints or bridged tracks.
4. Omitted part: Check off each construction step as you go.

MFJ-941EK Tuner Kit Instruction Manual
- 3 -
INTRODUCTION
Before soldering, always inspect leads and terminals for oxidation. If dull, clean
or burnish them with a small brass-wire hobby brush or glass-fiber brush
(available at Radio Shack). Clean surfaces and good heat distribution are the
keys to strong solder.
MFJ-941EK Parts Inventory:
Use the bill of material (BOM) on the next page to account for all the pieces in
your kit, checking each part off as you go. If there's a missing or damaged item,
write down the MFJ part number and contact MFJ for replacement (see Warranty
page for instructions). Most parts are packed in three plastic bags -- one for small
hardware items, one for pc-board components and pre-cut wire, and a third for
larger parts.
Figure 1.1: MFJ-941EK Tuner Kit

MFJ-941EK Tuner Kit Instruction Manual
- 4 -
INVENTORY
Begin your inventory with the hardware bag. For identification purposes, PH =
Phillips Head, SM = Sheet Metal Screw, SS = stainless steel, KEP = nut with an
integral lock washer, OD = Outside Diameter, and ID = Inside Diameter.
[X] Qty Description MFJ Part Number
[ ] 8 4-40 x 3/8" Machine Screw, PH 654-0375
[ ] 3 4-40 x 1/2" Machine Screw, PH SS 654-0500
[ ] 3 4-40 x 1/4" Threaded Aluminum Spacer 716B-0250
[ ] 11 4-40 Hex Nut, KEP 705-0440K
[ ] 2 6-32 x 1/4" Machine Screw, PH 656-0250
[ ] 1 6-32 x 1" Machine Screw, SS, PH 656-1000
[ ] 1 6-32 Hex Nut, KEP 705-0632K
[ ] 2 6-32 Hex Nut 705-0632
[ ] 1 6-32 Flat Washer 710-0643S
[ ] 2 6-32 x 1-1/4" OD Fiberglass Washer 714-06125
[ ] 1 6-32 x 1/4" Nylon Spacer 718-1218-0250
[ ] 8 #6 x 3/8" Screw, Sheet Metal, Black 656S-0375B-A
[ ] 2 #6 x 3/8" Sheet Metal Screw 656S-0375A
[ ] 2 10-32 x 3/32" Set Screw, Hex 660-0187-SA
[ ] 1 10-32 x 3/4" Machine Screw, PH 660-0750
[ ] 1 10-32 Hex Nut, KEP 705-1032K
[ ] 1 10-32 Wing Nut 705-1032S-W
[ ] 1 #10 Solder Lug 720E-0621L
[ ] 1 #10 Split Lock Washer 711-1037S-SL
[ ] 2 #10 Flat Washer 710-1050
[ ] 1 1/4" ID Heyco Shaft Bushing 740-2102
[ ] 1 1/4" ID x 1/2" OD x 3/4" Coupler, 10-32 725-3105
[ ] 1 1/4" x 3-1/2" Metal Shaft, 1/2" Flatted End 725-2112
[ ] 3 3/8" Hex Control Nut, Panel Mount 705-3732RI
[ ] 3 3/8" ID x 5/8" OD Flat Washer, Metal 710-3762
[ ] 1 3/8" ID x 5/8" OD Shoulder Washer, Fiber 714S-3762
[ ] 2 3/8" ID x 5/8" OD Flat Washer, Fiber 714-3762
[ ] 4 3/8" ID x 3/4" OD Flat Washer, Fiber 714-3775
[ ] 1 3/8" ID x 5/8" OD Flat Washer, Teflon 714-3762T
[ ] 4 3/8" ID x 3/4" OD Flat Washer, Teflon 714-3775T

MFJ-941EK Tuner Kit Instruction Manual
- 5 -
INVENTORY
Next, inventory the circuit board bag containing small pc-board components
and pre-cut wire. Color codes and number codes are included to help you sort
resistors, capacitors, and chokes.
[X] Qty Description MFJ Part Number
[ ] 2 100Ω1/4W Resistor (brown, black, brown) 100-2100
[ ] 1 150Ω1/2W Resistor (brown, green, brown) 101-2150
[ ] 1 3.3k 1/4W Resistor (orange, orange, red) 100-3330
[ ] 1 47K 1/4W Resistor (yellow, violet, orange) 100-4470
[ ] 4 50-K Trimpot, 10-mm Horizontal Mtg 133-4500B
[ ] 1 33pF Disc Ceramic Capacitor, 1kV (33) 200-0033-2
[ ] 1 220pF Disc Ceramic Capacitor, 1kV [phone]-2
[ ] 5 .01uF Disc Ceramic Capacitor, 50-V [phone]
[ ] 1 3-10 pF Trim-Cap, Horizontal Mtg 280-2010
[ ] 1 680 uH Choke (blue, gray, brown) 401-5680
[ ] 1 Directional-Coupler Xfmr, .37-OD Toroid 10-01003
[ ] 2 Schottky Diode, CDSH270 (or 1N270) 302-0270
[ ] 1 Switch, DPDT, Push-On/Push-Off 504-0022
[ ] 1 Switch, 4PDT, Push-On/Push-Off 504-0023
[ ] 1 2.1-mm PCB Power Jack 601-6021
[ ] 3 Hookup Wire, 5", Black 871-2400-0500
[ ] 1 Hookup Wire, 5", Red 871-2422-0500
[ ] 1 Hookup Wire, 5" Violet 871-2477-0500
[ ] 1 Hookup Wire, 5" White 871-2499-0500
[ ] 1 Tie Wrap, 4" Nylon 745-2149
[ ] 8 Buss Wire, 5-1/4", #16 Tinned 870-0016-0525
[ ] 1 Buss Wire, 6-1/2", #16 Tinned 870-0016-0650
[ ] 1 #4 Shoulder Bushing, Teflon 740-1012T
[ ] 1 Brass Eyelet (Small) 725-4108

MFJ-941EK Tuner Kit Instruction Manual
- 6 -
INVENTORY
This list covers the large item bag of larger items:
[X] Qty Description MFJ Part Number
[ ] 1 PC Board, Single-Sided 861-0949E
[ ] 3 Insulated Binding Post, Red, with Hardware 606-0003
[ ] 4 SO-239 UHF Chassis Mount Connectors 610-2005
[ ] 1 300-W 4:1 Balun on 1" Toroid Form 10-10002B
[ ] 1 2-1/2" Precision Cross-Needle SWR Meter 400-3083A
[ ] 1 Molded Plastic Meter-Mount Bracket 736-0201
[ ] 2 12 - 313 pF Air-Variable Capacitor 282-2006
[ ] 1 3/8" OD Plastic Pushbutton, Red 760-2140
[ ] 1 3/8" OD Plastic Pushbutton, Black 760-2122
[ ] 4 1/4" ID x 1" OD Knob, Black 760-0035
[ ] 1 Switch, 8PDT, 2-Section Rotary 500-0028-1
[ ] 1 2.1-mm DC Power Cable with Coax Plug 620-8321
Finally, these separate bag items are bagged seperately.
[X] Qty Description MFJ Part Number
[ ] 1 941E Inductor and Switch Assembly 10-13003
[ ] 1 MFJ-941E Aluminum Chassis 800-0941E
[ ] 1 MFJ-941E Front Panel Decal (pre-installed) 782-0941E
[ ] 4 Rubber Feet (pre-installed) 770-1162
[ ] 1 MFJ-941E Chassis Cover, Black 804-0941E
[ ] 1 Assembly and Operating Manual 925-0941EK

MFJ-941EK Tuner Kit Instruction Manual
- 7 -
CONSTRUCTION
Key Assembly Instructions:
Key words are used to shorten the length of the assembly steps to one line. Find
means to pull specific items from the parts inventory for installation. Identify
means to look for a mark or feature that orients the part for installation. Install
means to clean leads, insert them at a specified location, and bend or wrap them
so the part stays in place. Solder means to apply solder, inspect the connection,
and nip off protruding leads or pins. Legend refers to silk-screen lettering on the
printed circuit board.
Circuit Board Assembly:
Find the circuit board and take a minute to survey the component-side legend for
various part locations. When you're ready to begin construction, find the five
resistors listed below:
(2) 100 ohm (brown, black, brown)
(1) 150 ohm (brown, green, brown)
(1) 3.3K (orange, orange, red)
(1) 47K (yellow, violet, orange)
[ ] Install a 150 ohm 1/2-Watt resistor at R1 and solder.
[ ] Install a 3.3K resistor at R2 and solder.
[ ] Install a 100 ohm resistor at R3 and solder.
[ ] Install a 100 ohm resistor at R4 and solder.
[ ] Install a 47K resistor at R9 and solder.
Next, find four (4) 50K trimpots (black, 3/8" OD, 3 pins)
[ ] Install 50K at R5 and solder.
[ ] Install 50K at R6 and solder.
[ ] Install 50K at R7 and solder.
[ ] Install 50K at R8 and solder.
Find the four (4) disc ceramic capacitors listed below. Note that three leftover .01
uF capacitors will be installed later.
(1) 33pF (33)
(1) 220pF (221)
(2) .01 uF (103)
[ ] Install 33 pF at C3 and solder.

MFJ-941EK Tuner Kit Instruction Manual
- 8 -
CONSTRUCTION
[ ] Install 220 pF at C5 and solder.
[ ] Install .01 uF at C6 and solder.
[ ] Install .01 uF at C7 and solder.
Find the 3-10 pF trimmer capacitor (white ceramic, ~1/2" OD, 3 pins).
[ ] Install at C4 and solder.
On the pc board, locate the legend marking for C12 (next to trimpot R5).
[ ] Form a 1/4" jumper using a clipped-off lead end. Install at C12 and solder.
Find the 680-uH RF choke (blue, gray, brown).
[ ] Install 680-uH at L2 and solder.
Find two (2) Schottky diodes, CDSH 270 (blue) and identify the banded end.
Refer to Diagram 1.
Cathode End
Diagram 1: Diode Orientation
[ ] Install a diode at D1 with the banded end (cathode) toward the D1 legend.
[ ] Install the second diode at D2 with banded end toward the D2 legend.
Find the following items:
(1) Switch, DPDT, push-on/push-off (6 pins)
(1) Switch, 4PDT, push-on/push-off (12 pins)
(1) 2.1-mm PCB power jack
[ ] Install the DPDT switch at SW1. Confirm all pins are fully seated, and solder.
[ ] Install the 4PDT switch at SW2. Seat pins, and solder.
[ ] Install the 2.1-mm power jack at J1 and solder.
Find the 8PDT pc-mount 2-section rotary switch (from the larger parts bag)
[ ] Orient the switch over the pc-board legend at SW4 and install.
[ ] Confirm all pins are firmly seated and solder.

MFJ-941EK Tuner Kit Instruction Manual
- 9 -
CONSTRUCTION
Find the six (6) pre-stripped 5" lengths of jacketed hookup wire:
(3) Black
(1) Red
(1) White
(1) Violet
[ ] Locate three holes marked Ground on the edge of the pc board near R8.
[ ] Install a black wire in each and solder (free ends to be connected later).
[ ] Install a red wire at LMP (behind SW1) and solder.
[ ] Install a violet wire at FMTR (between SW1 and SW2) and solder.
[ ] Install a white wire at RMTR (opposite side of SW2) and solder.
Find the following items to construct SWR transformer T2.
(1) .37" OD toroid with bifilar winding
(1) #4 Teflon shoulder bushing
(1) Small brass eyelet
(1) 5-1/4" length of #16 buss wire
Refer to Diagram 2 below:
Buss Wire
Brass eyelet
Bend Wire Over
Solder to Pad
T2 Shoulder Bushing
BussWire
Top View
Install Toroid
Side View
Bushing
Install
In Eyelet
Install Eyelet and
1
2
3and Solder to Eyelet
5
Over Eyelet
4
Install
Shoulder
Install Wires and Solder
6
Diagram 2: SWR Transformer Installation

MFJ-941EK Tuner Kit Instruction Manual
- 10 -
CONSTRUCTION
[ ] Locate the pc legend for T2.
[ ] On the solder side, install the brass eyelet through the T2 pad, as shown.
[ ] Solder the eyelet flange in place, but do not fill the opening with solder.
[ ] Insert buss wire into the opening and make a 90-degree bend at the end.
[ ] Solder the bent end of the wire to the eyelet.
[ ] On the component side, install the toroid over the protruding eyelet.
[ ] Install the Teflon shoulder bushing on top, pressing it into the toroid center.
[ ] Confirm toroid is flush with pc board and wires aligned with mounting holes.
[ ] Install and solder all three leads (twisted tap lead goes in the center).
Find six (6) additional 5-1/4" lengths of #16 buss wire.
[ ] Install a buss wire at D/L and solder (rear of SW4)
[ ] Install a buss wire at WIRE and solder
[ ] Install a buss wire at COAX2 and solder.
[ ] Install a buss wire at COAX1 and solder.
[ ] Install a buss wire at C2 and solder (right front of SW4).
The sixth buss wire is connected between the pc board and a tab on SW4. Refer
to Diagram 3 below:
D/L
Wire
SW4
Connect
and Solder
Diagram 3: SW4 Tab Location
[ ] Install a buss wire at the unmarked hole between D/L and WIRE, and solder.
[ ] Locate the exposed solder tab on top of SW4's front wafer.
[ ] Route the buss wire to the designated terminal, install, and solder.
This completes circuit board sub-assembly. Note that several tuner models use
the same pc board and some parts locations are not used for this project. Before
moving on, take a few minutes to inspect and double-check your work.

MFJ-941EK Tuner Kit Instruction Manual
- 11 -
CONSTRUCTION
PC Board Installation:
Find the MFJ-941E chassis. Also, find the following hardware items:
(3) 4-40 x 1/2" Machine Screw
(3) 4-40 x 1/4" Threaded Aluminum Spacer
(3) 4-40 Hex Nut, KEP (nuts with lock washers)
Locate the three circuit board mounting holes on the bottom of the chassis.
These form a triangle -- two at the rear and one in front. Spacers are mounted as
shown below in Diagram 4:
KEP Nut
PC Board
Spacer
Screw
Chassis
Diagram 4: PC Board Mounting
[ ] Install spacers with 1/2" screws and spacer. Don't fully tighten.
[ ] Align and install the circuit board on top of the spacers.
[ ] Tighten the threaded spacers in place.
[ ] Secure the circuit board on top of spacers using KEP nuts.
Rear Panel Components:
Coax connectors are mounted from the inside of the chassis as shown below in
Diagram 5:
Diagram 5: Coax Mounting

MFJ-941EK Tuner Kit Instruction Manual
- 12 -
CONSTRUCTION
Find the following coax connector items:
(4) SO-239 female chassis-mount coaxial connector
(8) 4-40 x 3/8" Machine Screw
(8) 4-40 Hex Nut, KEP (nuts with lock washers)
[ ] Install a connector at COAX 1 and tighten hardware.
[ ] Install a connector at COAX 2 and tighten hardware.
[ ] install a connector at TRANSMITTER and tighter hardware.
[ ] Install a connector at DUMMY LOAD and tighten hardware.
On the pc board, locate the free end of each of the following wires and route
them to the designated connectors.
[ ] Route COAX1 buss wire to COAX 1 connector, trim, install, and solder.
[ ] Route COAX2 buss wire to COAX 2 connector, trim, install, and solder.
[ ] Route T2 buss wire to TRANSMITTER connector, trim, install, and solder.
[ ] Route D/L buss wire to DUMMY LOAD connector, trim, install, and solder.
Find the following Ground Post items:
(1) 10-32 x 3/4" Machine Screw, PHH
(1) 10-32 Hex Nut, KEP
(1) 10-32 Wing Nut
(1) #10 Solder Lug
(2) #10 Flat Washer
(1) #10 Split Lock Washer
Locate the ground-post hole (GND) on the rear panel. Refer to Diagram 6.
Screw Solder Lug
KEP Nut
Flat Washer (2)
Split Lockwasher
Wingnut
Groundpost Detail
Diagram 6: Groundpost Mounting
[ ] Install the solder lug on the screw and insert it out through back panel.
[ ] Install the KEP nut and tighten in place securely.
[ ] Install two flat washers

MFJ-941EK Tuner Kit Instruction Manual
- 13 -
CONSTRUCTION
[ ] Install the split lock washer.
[ ] Install the wing nut (loosely).
From the larger parts bag, locate the three red plastic insulated terminal posts.
Confirm that each one has a mating lock washer and nut. Install according to
Diagram 7.
Lockwasher
Nut
Diagram 7: Groundpost Mounting
[ ] Install a terminal post at WIRE on the back panel (next to GND) and secure.
[ ] Install two terminal posts at BALANCED LINE and secure.
[ ] On the pc board, locate the buss lead labeled WIRE.
[ ] Trim and install it on the WIRE terminal post. Solder.
Find the following components to install the 300-W 4:1 Balun:
(1) 300-W, 4:1 Balun on 1" Toroid Form
(1) 6-32 x 1" Machine Screw, SS, PH
(1) 6-32 Hex Nut, KEP
(1) 6-32 Flat Washer
(2) 6-32 x 1-1/4" OD Fiberglass Washer
(1) 6-32 x 1/4" Nylon Spacer

MFJ-941EK Tuner Kit Instruction Manual
- 14 -
CONSTRUCTION
On the chassis, locate the balun transformer mounting hole (approximately 2" in
front of the terminal posts and ground post). Refer to Diagram 8 below:
KEP Nut
Metal Washer
1-1/4" FG Washer
4:1 Balun
1"Screw
1/4" Spacer
Diagram 8: Balun Mounting
[ ] Insert the 1" machine screw up through the bottom of the chassis.
[ ] Install a 1-1/4" fiberglass washer followed by the 1/4" nylon spacer on top.
[ ] Install the balun over the spacer, orienting leads toward the back panel.
[ ] Install the second 1-1/4" fiberglass washer to sandwich the balun in place.
[ ] Install a #6 flat washer and KEP nut. Tighten, but don't crush balun windings.
[ ] Locate B&W twisted lead on balun. Install on the ground-post lug and solder.
[ ] Trim and install the white lead on either BALANCED LINE post and solder.
[ ] Trim and install the black lead on the other BALANCED LINE post and solder.
Find the following items to prepare for installing the SWR meter:
(1) 2-1/2" Precision Cross-Needle SWR Meter
(1) Molded Plastic Meter-Mount Bracket
(2) #6 x 3/8" Sheet Metal Screw
(3) .01 uF Disc Ceramic Capacitors (marked 103)

MFJ-941EK Tuner Kit Instruction Manual
- 15 -
CONSTRUCTION
Refer to Diagram 9 below during meter installation.
Locate the adhesive foam-tape pad adhered to the rear of the meter assembly.
This pad is installed to cushion the meter bracket and provide tension. Do not
remove the protective layer of tape to expose the adhesive underneath!
.01
.01
.01
++
-
-
Red
Violet
White
Black (3)
Slide Meter Onto
Meter Bracket
1
Move Bracket
into Mounting
Location
2
Secure with
3/8" SM Screws
3
and Meter
Foam
Pad
Wiring Meter
Mounting Meter
Diagram 9: Meter Mounting and Wiring
[ ] Locate the lamp assembly that protrudes from the back of the meter.
[ ] Orienting the bracket as shown, gently lower the meter onto it.
[ ] Move into mounting position, aligning meter face with the panel opening.
[ ] With bracket aligned on mounting holes, install using two #6-3/8" SM screws.
Refer to Diagram 9 wiring pictorial, install the .01 capacitors and hookup wire
leads as shown:
[ ] Install a .01 uF capacitor across the (+) and (-) terminals of each meter.
[ ] Install a .01 uF capacitor across the terminals of the lamp assembly.
[ ] Trim and install a black wire to the minus (-) terminal of each meter.
[ ] Trim and install a black wire to either terminal of the meter lamp assembly.
[ ] Trim and install the (FMTR) violet lead to the (+) terminal, side meter.
[ ] Trim and install the (RMTR) white lead to the (+) terminal of the right meter.

MFJ-941EK Tuner Kit Instruction Manual
- 16 -
CONSTRUCTION
Find the following parts for installation of the tapped tuning inductor:
(1) Tapped Air-Wound Inductor and Switch Assembly
(1) 3/8" Hex Control Nut, Panel Mount
(1) 3/8" ID x 5/8" OD Flat Washer, Metal
(1) 3/8" ID x 5/8" OD Shoulder Washer, Fiber
(1) 3/8" ID x 5/8" OD Flat Washer, Fiber
(2) 6-32 x 1/4" Machine Screw, PH
(2) 6-32 Hex Nut
Look inside the air-wound inductor to locate two protruding solder lugs (see
Diagram 10 below). These lugs will be used to attach the inductor to the chassis.
Also, note that the frame of the wafer switch will be isolated from chassis ground
using fiber washers. The shoulder washer centers the switch in the panel
opening.
Shoulder Washer
Flat Fiber Washer
Flat Metal Washer
Control Nut
Inductor Switch
Mounting
Lugs
Diagram 10: Inductor Mounting
[ ] Install the fiber shoulder washer on the Inductor switch, as shown above in
Diagram 10.
[ ] Insert the switch shaft at INDUCTOR and align coil lugs with chassis holes.
[ ] Install two 1/4" screws up through the chassis and secure coil with hex nuts.
[ ] Seat the switch and confirm that the shoulder washer is centered in the hole.
[ ] Install a 5/8" fiber washer, metal washer, and control nut. Tighten in place

MFJ-941EK Tuner Kit Instruction Manual
- 17 -
CONSTRUCTION
Like the Inductor switch, the Transmitter and Antenna tuning capacitors are
isolated from the chassis by non-conductive washers. The Transmitter control
uses fiber washers and the Antenna control uses Teflon washers. Find the
following items:
(2) 12-313 pF air-variable capacitors
(2) 3/8" Hex Control Nut, Panel Mount
(2) 3/8" ID x 5/8" OD Flat Washer, Metal
(1) 3/8" ID x 5/8" OD Flat Washer, Fiber
(2) 3/8" ID x 3/4" OD Flat Washer, Fiber
(1) 3/8" ID x 5/8" OD Flat Washer, Teflon
(2) 3/8" ID x 3/4" OD Flat Washer, Teflon
Flat 3/4" Insulating Washer
Flat 5/8" Metal Washer
Control Nut
Flat 5/8" Insulating Washer
Flat 3/4" Insulating Washer
Stator
Rotor
Diagram 11: Capacitor Mounting
[ ] Install a 3/4" fiber flat washer on one of the variable capacitors.
[ ] Insert the shaft at TRANSMITTER with the stator to the right side, as shown in
Diagram 11.
[ ] From the front, install a 5/8" fiber washer, centering it in the hole.
[ ] Install a 3/4" fiber flat washer, a 5/8" metal washer, and a control nut. Secure.
Repeat the same procedure for the Antenna capacitor using the three Teflon flat
washers.
[ ] Install the other capacitor at ANTENNA, as shown.

MFJ-941EK Tuner Kit Instruction Manual
- 18 -
CONSTRUCTION
Looking at the coil assembly, you'll see that the top winding has been cut and is
isolated from the remainder of the coil. This wire is used to connect the stator of
C1 to the pc board. It will be pulled back from the two front retainer rods and
routed as shown below in Diagram 12:
C1
Stator
Rotor
Solder to Switch
Tab Adjacent
To C1
Antenna
Capacitor
Coil Wire
Buss
Wire
Buss
Wire
C2 Stator
Rotor
Tap
Coil
Top
of
Coil
Onto
End
Diagram 12: Wiring Detail
[ ] Carefully remove the top wire from the two front retainers, as shown.
[ ] Trim and install the right lead end to the stator of the Antenna capacitor.
[ ] Trim and solder the left lead-end to the switch tab adjacent to C1 at SW4*
*The pad at legend C1 and the exposed tab on SW4 are common to each other.
Connecting the buss wire directly to the switch tab is simpler than lifting the
board to solder it in at C1.
To complete tuner wiring, find the remaining #16 buss wire.
[ ] Trim and install a buss wire onto the rotor tab of the Antenna capacitor.
[ ] Install the opposite end as a tap on the exposed inductor winding, as shown.
Locate the left front retaining rod of the Inductor. There will be a curled-back
wire-end at that location. That is the top end of the tuner coil.
[ ] Install a length of buss wire onto the top winding of the coil (at left-front rod).
[ ] Trim and install the opposite end to the Transmitter capacitor stator post.
[ ] On the pc board, find the buss wire installed at C2.
[ ] Install the opposite end to the Transmitter capacitor rotor tab (C2).

MFJ-941EK Tuner Kit Instruction Manual
- 19 -
CONSTRUCTION
Tuner wiring is now complete. Before going on, check all solder connections and
hardware for security. The next stage is final assembly.
Find the following items to complete the Antenna Selector Switch assembly:
(1) 1/4" ID Heyco Nylon Shaft Bushing
(1) 1/4" ID x 1/2" OD x 3/4" Shaft Coupler
(1) 1/4" x 3-1/2" Metal Shaft with 1/2" Flatted End
(2) 3/32" x 10-32 set screw, hex head
(1) 1" OD Knob, Black with Silver Insert
Install the Antenna Selector shaft and knob as described below:
[ ] Insert the Heyco nylon bushing into the front panel at Antenna Selector.
[ ] Start two #10 Allen set screws into the shaft coupler (3/32" Allen Wrench).
[ ] Install the shaft coupler on SW4. Secure rear set screw with a Allen wrench.
[ ] Insert round end of shaft through the front panel bushing and into the coupler.
[ ] Temporarily secure front set screw using an Allen wrench.
[ ] Install the 1" knob, aligning its set screw with the flatted side of the shaft.
[ ] Tighten the knob in place with a 5/64" Allen wrench.
[ ] Rotate the switch fully counter-clockwise to its stop.
[ ] Loosen front shaft-coupler screw, rotate knob to Dummy Load on the left side.
[ ] Re-tighten the coupler set screw. Rotate knob and confirm pointer alignment.
Find these remaining items to complete final assembly:
(3) 1" OD Knob, Black with Silver Insert
(1) 3/8" OD Plastic Pushbutton, Red
(1) 3/8" OD Plastic Pushbutton, Black
[ ] Fully mesh Transmitter capacitor plates. Install knob with pointer at "0".
[ ] Fully mesh Antenna capacitor plates. Install knob with pointer at "0".
To align the knob on the Inductor switch, first locate the switch's "home" or open
position. Looking at the rear of the switch wafer, the wiper ring and selector tab
should be aligned, as shown below. If not, temporarily install a knob and advance
the switch until the two are aligned. See Diagram 13.