Consolidated Construction Manual
38 Special
(a kit by NorCal QRP Club)
(all information here is gleaned from the internet, or
uses the 38 Special Manual as a guide. The copyrights
are retained by their original authors, Doug KI6DS and
Ori AC6AN, and grateful thanks is offered for their
permission to re-write their work)
I ended up frying the IC's in my first 38 Special kit,
and decided to build another. Several of the mods and
problems I encountered left me confused, so with the
goal of building a neat, professional-looking radio, I
decided to develop this construction manual, with the
mods integrated into the construction of the initial
rig. This manual is not a substitute for the original
38 Special manual, only a supplement. The original
manual is well-written, but not idiot-proof. Since I'm
an idiot, I need this "expanded" manual.
Each construction step has potentially several parts.
The first is called "Stock" and relates to those
components that are for the stock (unmodified) radio.
The mods included in this construction manual are the
most stock: the TiCK Keyer, the 5 watt mod using an
IRF 510 final amplifier, and the RIT mod. In addition,
I've included some mods that I plan to make on my
radio, like continuously variable RF Output control,
and increased TiCK sidetone. These mods are from the
Internet, and have not been tested.
Most people I've talked with seem to indicate the RIT
mod to cause more problems than perhaps it solves - the
radio seems to be less stable. I don't plan on doing
this mod, but added it here for convenience. Other,
more "esoteric" mods can be gleaned from QRP-L.
I would recommend one thing, though. If this is your
first kit, or if you aren't confident of your building
skills, build the radio stock first - no mods,
including no 5-watt or TiCK mod. Any modification that
involves a trace cut shouldn't (IMHO) be done until the
rig is verified as performing "on specs." I'm
discovering the hard way that mods have a way of
sneaking up on you, and making the process of debugging
the radio ever-so-cumbersome. I've also added to the
end of this manual Ori's superb troubleshooting guide,
and a few of my own notes on debugging my radio, which
I hope will be of assistance to the first-time
builder/debugger.
If this document provides assistance and enjoyment in
constructing the 38 Special, I will have achieved my
goal. Ori, Doug, Jim, and the gang at NorCal has
provided us with a wonderful opportunity. I hope
instead of compensation, that operating the rig will be
foremost in your mind, and that you will faithfully QSL
every contact made with the radio. That is
compensation enough for me!
Marty Watt, KM7W
Jackson, Tennessee
Stock:
Wind the toroids and transformer per the
instructions in the original 38 Special
manual. Do not install at this time!
(Note: problems in peaking the receiver on
alignment seems to indicate a problem with the
toroidal transformer, T1. Removal of 1 to 2 turns
on the secondary of the T1 transformer seems to
solve the receiver alignment problem. Two
distinct peaks while adjusting TC1 are a must - if
you don't get two peaks, T1 is suspect.)
5-Watt Mod:
Wind L101, 27 Turns on a Red T37-2 core.
Stock:
Install the 12 MHz crystals. There are ground
pads provided on the top of the board near the
crystals, but I'm not sure if these areas are
usable or not. In any event, a short wire from
the case of the crystal to ground (somewhere) is
required to stabilize the crystal operation.
Stock:
Install the 5 ICs in the places provided.
Carefully observe the orientation of the IC
sockets with the notch aligned with the notch
on the silkscreen. Back ohm ards IC's
generally don't work. Socketing the ICs is
mandatory, in my opinion, as stability is not
affected, and the board is so well-done is
doesn't lend itself to unsoldering IC chips.
TiCK Keyer:
Socket U6, the socket for the TiCK keyer
chip. Note that the chip instructions
recommend socketing. Check the orientation
carefully! My chip had a notch and a red
dot. Per Gary at Embedded Research, the dot
indicates the chip type to the manufacturer,
NOT pin 1. Align the notch, not the dot!
Stock:
Install TC1 and TC2, paying close attention
to orientation. The flat side of the
capacitor should match the flat side on the
silkscreen.
Stock:
Install diodes and transistors, noting
correct orientation (banded end on diodes,
flat side on transistors in TO-92 cases)
D1 - 1N4007
D2 - 1N4007
D3 - 1N4004
D4 - 1N914
D5 - 1N914
D6 - 1N914
D7 - 1N914
D8 - 1N914 (Note: Do not install if doing 5-watt
mod!)
5-Watt Mod:
Install wire jumper in D8.
TiCK Mod:
Install VR201 - 78L05 regulator in TO-92
case.
Install TR201 - 2N2222 or 2N3904
transistor in TO-92 case.
RIT Mod:
Install D301 - 1N914
Install D302 - 1N914
Stock:
Install resistors
R1 - 1.3k ohm brn/org/red
R2 - 1.3k ohm brn/org/red
R3 - 1.3k ohm brn/org/red
R4 - 10k ohm brn/blk/org
R5 - 3.9k ohm org/whi/red
R6 - 1.3k ohm brn/org/red
R7 - 3.3k ohm org/org/red
R8 - 18k ohm brn/blk/org
R9 - 10k ohm brn/blk/org
R10 - 27k ohm red/vio/org
R11 - 6.8k ohm blu/blk/red
R12 - 2.2k ohm red/red/red
R13 - 470 ohm yel/vio/brn
R14 - 2.2k ohm red/red/red
R15 - 150k ohm brn/grn/yel (Note: Do not install
for TiCK Keyer Mod)
R16 - 68k ohm blu/blk/org (Note: Do not install
for TiCK Keyer Mod)
R17 - 2.2M ohm red/red/grn (Note: Do not install
for TiCK Keyer Mod)
R18 - 30k ohm org/blk/org
R19 - 4.7k ohm yel/vio/red
R20 - 270 k ohm red/vio/yel
R21 - 510ohm grn/brn/brn
R22 - 390ohm org/whi/brn
R23 - 33k ohm org/org/org
R24 - 47 ohm yel/vio/blk (Note: Do not install
for "More Audio" Mod)
R25 - 30k ohm org/blk/org
R26 - 30k ohm org/blk/org
More Audio:
Place wire jumper in R24, instead of 47ohm
resistor
TiCK Keyer:
R17 - 270k ohm red/vio/yel for loud sidetone
560k ohm grn/blu/yel for medium sidetone
1M ohm brn/blk/grn for quiet sidetone.
Leave R15 and R16 open
R202 - 10k ohm brn/blk/org
5-Watt Mod:
R102 - 220 ohm red/red/brn (do not install if doing
variable power out mod!)
R103 - 10k ohm brn/blk/org (do not install if doing
variable power out mod!)
R104 - 10 ohm brn/blk/blk (add ferrite bead to leg of
R104 installed closest to
R103 prior to installation)
Variable Power Out mod:
(Note: Some internet users question whether or
not this mod drives the final PA too hard.
However, all this mod does is allow you to vary
the voltage provided to the IRF510 from 0-max with
the normal 5 watt mod installed)
Install 22 k ohm resistor on one end of 50 k
ohm pot (any value between 25-100k ohm should
be fine)
Solder wire to other end of the 22 k ohm
resistor.
Solder other end of the wire to the cathode
(banded) end of D7.
Solder wire from other side of pot to top
(ground) hole of R102
Solder wire from center of pot to the bottom
hole of R102 (where R102 and C102 join). If
voltage is maximum when pot is turned counter-
clock wise, then reverse the connections at
the ends of the pot.
Stock:
Install disc capacitors, except C7 and C11:
C1 - 0.01 uF
C2 - 0.01 uF
C3 - 150 pF
C4 - 0.01 uF
C5 - 0.1 uF
C6 - 0.01 uF
C8 - 47 pF
C9 - 39 pF
C10 - 12 pF
C12 - 0.1 uF
C13 - 0.1 uF
C14 - 0.01 uF
C16 - 22 pF
C17 - 47 pF
C18 - 0.1 uF
C19 - 47 pF
C20 - 47 pF
C21 - 47 pF
C22 - 100 pF
C23 - 22 pF
C24 - 0.1 uF
C25 - 0.01 uF
C26 - 220 pF (Note: Do not install for "5 watt" Mod)
C27 - 0.1 uF
C30 - 0.1 uF
C31 - 0.01 uF
C32 - 220 pF
C33 - 0.01 uF
C34 -- 0.001 uF monolythic
C35 - 0.1 uF
C36 - 0.1 uF
C39 - 0.1 uF
C41 - 0.1 uF
C42 - 0.1 uF
C43 - 0.1 uF
C44 - 0.1 uF
TiCK Keyer Mod
C202 - 0.1 uF monolythic
5 watt Mod:
C26 - 330 pF disc
Wire jumper C101 (Note: Do not wire jumper if doing
variable power out mod)
C102 - 0.1 uF monolythic
C103 - 0.1 uF monolythic
Variable Power Out mod:
C101 - 0.1 uF monolythic
Stock:
Install X2, the 22.118 MHz crystal. Be sure
to solder the can to the ground plane via the
silver tabs provided on the top side of the
board.
Stock:
Install remaining disc and electrolytic
capacitors:
C7 - 47 pF
C11 - 5 pF
C15 - 22/16V Electrolytic
C37 - 22/16V Electrolytic
C38 - 22/16V Electrolytic
C40 - 220/16V Electrolytic
Stock:
C28 - 820 pF silver mica or polystyrene (Note: Do not
install for "5 watt" Mod)
C29 - 560 pF silver mica or polystyrene (Note: Do not
install for "5-watt" Mod)
5 Watt Mod:
You have a decision to make! The original mod
indicates the first set of components. Further
testing has "optimized" the output network at the
second set of values. Something in these ranges
should work - but the second method is supposed to
suppress harmonics and peak power output slightly
better. Choose your values!
C28 - 820 pF silver mica or polystyrene
C29 - 560 pF silver mica or polystyrene
C501 (on board, C505 on schematic) - 330-560
pF silver mica or polystyrene
OR
C28 - 1000-1200 pF silver mica or polystyrene
C29 - 560 pF silver mica or polystyrene
C501 (on board, C505 on schematic) - 560 pF
silver mica or polystyrene
Stock:
L1 - 4.7 uH choke (see freq coverage notes
below - do not install if doing RIT mod!)
L2 - 20 Turns
L3 - 8 Turns
L4 - 12 Turns
5 watt Mod:
L5 - 27 Turns
RIT Mod:
L1 - 6.8 uH choke
Frequency coverage is (by and large) determined by
the value of L1. Some got better coverage without
the RIT mod by changing L1 to a 5.6 or 6.8 uH
choke. The frequency range typically drops lower,
and can be brought up with the use of a variable
cap in line with the choke. Other methods involve
winding a few more turns on the existing molded
choke, to one end. The new windings are connected
to the end of the existing choke, and the winding
is soldered to the board. If the frequency moves
in the wrong direction, wind in the opposite
direction. Only a few turns are needed - 5 to 6
perhaps.
In my case, the stock frequency coverage was
10.101 to 10.124. I was pretty happy. 20 kHz is
about all one can expect out of a VXO without
creating instability problems, drifting, chirping,
and other "omygoshwhyisitdoingthis?" items.
Stock:
Install T1 - insert and solder primary (ends C&D
per the manual) first, then the secondary (A&B per
the manual).
Stock:
Install VR1, the 7808 regulator, flat tab to the
outside of the board.
5 watt mod:
Install TR101, the IRF510 Final PA
transistor. Pay close attention to the
information in the manual regarding grounding
the tab - DON'T!
TiCK mod:
Install TiCK chip into socket.
All mods, trace cuts:
Pay attention to the manual, and cut the required
PC board traces for the mods you are performing.
TiCK mod, cut trace marked by "2" on the
diagram in the manual.
5-watt mod, cut trace marked by "1" on the
diagram in the manual.
RIT mod, cut trace marked by "3" on the
diagram in the manual.
Additionally, if you are performing the "Louder
TiCK sidetone" mod, do the following:
Find the trace that connects C15, C32, and
R19. It is a dogleg trace between U2 and U4.
C32 connects via a "stubby" trace about
halfway on the longer trace between C15 and
R19. Cut the stubby trace (and C32 is thus
cut out of the circuit).
Install a 4.7 k ohm (yel/vio/red) resistor
from the end of C32 you just cut out to pin 6
of U5. This mod puts the TiCK keyer sidetone
into the Audio chain via it's own 4.7k ohm
resistor, rather than through R19/R20.
Stock:
Install off-board connections per the manual.
Tuning pot, 100 k ohm, high end to pad 18,
mid to pad 17, and low to pad 16.
Note that better tuning linearity is achieved
by using an AUDIO taper pot for the 100 k ohm
tuning pot. Linear pots (I discovered) don't
work very well.
RF gain, either a 1k or a 5k pot will
suffice, linear taper is fine. High to pad
13, mid to pad 12, low to pad 11.
If installing the RIT mod, you'll need a 10 k
ohm pot. High to pad 14, center and low tied
together and soldered to tuning pot.
Variable RF output mod requires a 50 k ohm
pot. Installation outlined above.
Key input Stereo Jack, Tip to pad 9, Ground
to pad 10 (watch this - the jacks will fool
you!) - if installing the TiCK chip, see
below, and do not install this jack.
Power connection, positive to pad 3,
negative/ground to pad 4. Feel free to add a
toggle switch and a fuse if desired,
somewhere in the positive lead.
TiCK mod:
Paddles input stereo jack, tip/dit
paddle to pad 6, mid/dah paddle to pad
7, ground to pad 5.
Install the normally open, momentary
SPST switch, one end to pad 5 and the
other to pad 10.
Stock:
Place chips in sockets if not done earlier.
Align per instructions. If you do NOT get two
peaks of audio when turning TC1, consider taking a
turn or two off of T1 secondary until you DO get
two peaks. These "twin peaks" are critical to
receiver alignment.
If you have installed the TiCK keyer mod,
transmitter alignment without a scope is not
recommended, but can be done by monitoring the
transmitted (dummy loaded!) tone through a general
coverage receiver, and adjusting TC2 for best
tone, not necessarily power out. Tune around as
well and check for minimal spurs. Most signal
spurs are around 9.0 to 9.5 MHz, if at all. Check
with a scope at the first opportunity!
Mount in case of your choice.
If something doesn't work, proceed to Ori's
"debugging basics" which are included with this
document.
ENJOY!
A Debugging Primer (by Ori, AC6AN)
This text describes the basic troubleshooting procedure
for the "38 Special" transceiver. There are different
levels of tests possible, depending on the test
equipment on hand. In an attempt to simplify things,
this text concentrates on the basic tools available to
most potential builders of the kit. Brief references to
more advanced tests are also included where
appropriate.
General "dead" Transceiver Procedure
(1) Apply power briefly and touch all ICs. None should
be more than lukewarm. Anything else and you have
a problem around the "hot" chip.
(2) When any part of the design is suspected "dead"
the first step is to test all power supply
connections (referenced to ground):
(a) 12V at the power connector
(b) 8V at all ICs as follows (IC/pin): U1/8,
U2/14, U3/8, U4/20, U5/8
(3) Other DC voltages:
(a) verify about 4V at U5 pins 3 and 5.
(b) check the base of TR1 (2N3904, middle pin) as
follows:
about 0.6V on receive (key open)
about 1.5V on transmit (key down)
(c) check U2/12, U2/13, U4/1, U4/13, banded side
of D6:
8V on receive (key open)
0V on transmit (key down)
(d) check U2/5, U2/6, U4/7, banded side of D1 and
D2:
5V on receive (key open)
8V on transmit (key down)
(e) check DC voltage on banded side of D3, while
varying the tuning pot position for 0-8V
voltage range. Any problem with the DC
voltage levels mentioned means you have
something wrong in that area of the board.
These tests can be done even with a cheap
analog voltmeter.
(4) Verify sidetone with key down. If you hear the
sidetone then the audio stage is OK and most
likely U4 is not faulty. In general, we found
that the ICs are very rugged. Do not remove an IC
from the board before you have verified all
components around it first!
Basic Receiver Tests
It is assumed that the DC tests checked OK.
(1) First test that the headphone jack is compatible
with the socket.
(2) You should hear the sidetone with key down. This
tells us that the audio amp circuit (U5) is
functioning.
(3) If no sidetone heard, the audio amp might still be
OK:
(a) Listen with the headphones while touching
different places in the receive path with a
metalic object (screwdriver, etc.). You
should hear some noise in the headphones
(possibly you'll pick up a local AM station,
due to the high gain):
U5/2, U5/6
U2/10, U2/11, U3/4
U3/1, U2/2
U3/6, U3/7 (both are part of the 12.0 MHz
oscillator)
U2/1
U1/4 (if U2/1 was OK and this one is dead,
then check the crystal filter)
U1/6, U1/7 (both are part of the 22.1 MHz
oscillator)
U1/1
banded side of D1 and D2
antenna connector (center pin)
The above procedure tests the receive chain
"back ohm ards". If you stop hearing at a
particular point, check the circuit in
between that point and the previous ("good")
point.
(4) If you have a general-coverage receiver, "listen"
to the 12.0 and the 22.118 MHz oscillators around
those nominal frequencies. Use a short wire for
the antenna of the test receiver and place it
close to the "38 Special" board, while applying
power. Check that the 22.118 MHz signal varies
when you change the position of the tuning pot.
Check that the 12.0 MHz moves down about 600 Hz
with key down vs. key open. This step verifies
that the oscillators are functioning correctly.
This step can be also executed with a scope and a
frequency counter (make sure the probe is not too
capacitive).
Basic Transmitter Tests
It is assumed that the DC tests checked OK.
(1) You should hear the sidetone with key down,
assuming you verified that the audio amp is
functional. Lack of a sidetone may mean that the
sidetone circuit is faulty or that U4 has some
problem. Do not remove U4! Check all other
components around it first.
(2) With a general-coverage receiver, you should hear
a carrier around 10.110-10.130 with key down. Tune
the transmit trimcap TC2 and scan that range with
a short wire as an antenna on the test receiver.
You should use a 50 Ohm load for the "38 Special"
for this test. In general, the sidetone on a
stock kit will sound harsh when it's not tuned
correctly, so this should be used as the first
indication of correct transmitter tuning.
(3) Verify that the oscillators are working correctly,
as described in the previous section (basic
receiver tests). The correct operation in receive
mode is satisfactory.
(4) All other transmit chain tests require a scope.
Signal levels in the transmit chain are viewable
on all scopes (at least 100 milivolts p-p) and
should be easy to trace. You should be looking
for a clean sinewave at the base of TR1 with key
down, and check for about 2.5 p-p swing on its
collector. On the dummy load at the antenna
connector you should see a few volts p-p swing and
very clean sinewave at the 10.110-10.130 MHz
range.
(Editor's note: the Base of TR1 can be measured
at the junction point of R10 and R11. Collector
measurements can be made at R12, Emitter at R13)
More detailed description of signals is beyond the
scope of this basic debugging procedure, and may appear
in a future article.
72 es 73 de
Marty, KM7W
__________________________________________________________________
Jackson, Tennessee e-mail: mdwatt@usit.net
http://www.public.usit.net/mdwatt
"The Curmudgeon's Corner"
NorCal #???? - ARCI #7514 - QRP-L #953 - AK/QRP #098 - Grid EM55oq
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