The Xtal Set Society Newsletter

Volume 11, No. 4 July 1, 2001

In this issue (#61) July 1, 2001

DXer, 2 Tube Regen SW Receiver

Iron Pyrites Negative Resistance Oscillator

On Q

Various Notes on the Variometer

Dxer, Two Tube Regenerative SW Receiver

“The Peebles Choice”
By Mike Peebles

A couple of issues ago, we made a nice little two tube

audio amplifier. The short wave set in this issue has
been in the back of my head for a long time. Allied

Figure 2: DXer Parts Layout

ment tubes), such as this article. I won’t take up a lot

of space for further explanation here, but it would be
interesting research for those of you who like to “dig
up” that sort of stuff. The set in this issue is designed
to be a mate to the aforementioned audio amp, and it
is a hot little set. One thing I learned from this set,
and from studying Doerle, is that you can hear around
the world with these sets using a whip antenna and a
good ground. No fooling, try it! With a set of three
plug-in coils, it will cover approximately 1.65 MHz to
18.5 MHz. This set is a little advanced, but I’ve tried
Figure 1: DXer Receiver w/ Audio Amp, and XS-105 to make the instructions so that most people could
Power Supply Kit. build it. I am also just an e-mail away for help.

Radio’s Knight kit line had a two tube,

battery operated set called the Dxer. It
was a little known set. I’m not certain
when it was produced, but my guess
would be early ‘50s. The set in this issue
is inspired by that set, but it is quite dif-
ferent. This set is a modified “Doerle”; the
Knight set did not have an inter-stage
transformer. For those of you who do not
know what a Doerle is, it was a series of
sets designed by a man of that name,
and it was very popular among experi-
menters and SW listeners in the ‘20’s
era. His sets were basically two tubes
(triodes - three elements) with a 1:3 ratio
inter-stage transformer between the
detector stage and the audio stage. Later
the sets were modified, added to,
changed, and eventually someone
designed a series with pentodes (five ele-
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 1
See Figures #3 and #4: The signal is introduced to the method used. Too much gain will put the circuit into
set via C-1, which helps as a neutralizer to help elim- oscillation, and too little will degrade the sensitivity of
inate “empty spots” throughout the bands. L-1, C-2a the circuit. The trick is to hit the happy medium,
or C-2b and C-3 make up the tuning circuit, which which comes from a little patience and practice. After
separate the desired signals. The signal is then passed all, the only way to get to Carnegie Hall is, “practice,
through C-4 into the first grid of V-1 (Pin #6). C-4 and young man, practice!”, exclaims the elderly cello play-
R-1 act as the detector (grid-leak) circuit. The signal er. C-5 and C-6 are used for bypassing purposes, and
is amplified onto the plate (Pin #2) of V-1. L-2 is con- I won’t get real technical about that here. B+ potential
nected to the plate of V-1 and serves as “feedback” to to the plate of V-1 is provided through Pins #5 and 4
L-1, as the process of re-amplification of the signal of IT-1. Since all this previous signal amplification is
occurs. The amount of feedback is controlled by R-2, actually audio content (detection occurred at C-4 and
on Pin #3 of V-1. As R-2 increases the B+ potential on R-1), it is then passed on through L-3, choking out
the second (control) grid of V-1, the amount of gain in any stray RF content, to the primary of IT-1. IT-1’s are
the tube increases. This is also known as the “regen- interesting little transformers. By accident, I discov-
eration control”, which I believe is the most efficient ered these to be great 1:3 ratio audio (rare) trans-
formers (I was about to throw them out). I purchased
them to serve as small B+ supplies, and they failed. I
told Dan Petersen, “I’ll bet these will work for an audio
interstage transformer.” Dan grunted, “perhaps,” as
he carried them back from my pickup, which was
headed back to the surplus store. The signal through
IT-1 is amplified again through the turn’s ratio of IT-
1 and amplified a third time through V-2. I found that
coupling the IT-1 transformer to V-2, via C-2 and R-4
as the grid bias, was more efficient than the conven-
tional way of “hanging” the secondary onto the tube’s
grid. Another unconventional thing is the R-5 load
resistor on V-2’s plate, with the audio passing
through C-9 to the set’s audio output. This is done to
allow varied types of audio reproduction devices. The
set will accept loads of 1k to 5k and above. Thus,
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 2
 C-3 is not real critical, but I removed all the
plates, except for two. This will help to spread the
“band-spread” to the best limits. C-4 and C-5
should be silver mica units, but if you’re not using
the set in Antarctica, then standard units should
be stable enough for most practical purposes. The
layout and wiring of V-1 and all associated parts
should be kept short, sound, and direct as possi-
ble. The backside of the front panel should be
lined with aluminum foil and grounded (or made
of metal and grounded). This reduces “hand-
capacity”, which will de-tune the circuit as your
body comes closer to the receiver. This is very
aggravating when you are trying to precision tune
the set. The shown layout of the set matches the
audio amplifier from the March 2001 issue of the
newsletter, but this does not need to be followed
exactly.

Scott Balderson’s nice 1k surplus phones work nice-

ly. Scott, those are great headphones...my set came
all the way from Australia, but what the hey!

Let’s build it! See Figure’s 3-8 for the basic construc-
tion details, referring to the parts list for correct com-
ponents and suggestions for obtaining them. It may
be difficult to obtain the exact values for C-2a and C-
2b. If you get something close, it will work OK. If
you’re fussy about exactness, then add a turn or two
on L-1 for smaller values and vice versa for larger val-
ues.

The performance and ease of use would be greatly

enhanced with the following modifications: 1) Use a
vernier dial on R-2 or place a second, smaller pot in
series with R-2 (about 5k or less). Regeneration con-
trol is very critical, as you’ll find-out, and works more
nicely with these suggestions, and; 2) Use a vernier
dial on C-3 (band-spread), as this is a critical adjust-
ment, especially the higher you go in frequency. You
can obtain these controls from some of the vendors
I’ve suggested, but get out your heart pills when you
see the price…ouch!

Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 3
 See Figure 9 (page 3) for coil winding.
Be certain to take special note of the J-
1 jumper and its positions for each
coil. Thoroughly sand the insulation
from the magnet wire. Tin and care-
fully solder each wire into its respec-
tive pin in the octal socket. Keep these
wires as short and direct as possible
without allowing them to cross each
other. The windings on the spaced
coils do not need to be spaced exactly,
but the overall length is critical.

Operating the set is tricky and takes

patience and practice. Here are a few
hints: 1) Use a good earth ground; 2)
Most antenna situations work, even a
whip antenna mounted as high as pos-
sible. Mine is mounted toward the ceil-
ing of my radio shop, and I heard stuff
from all around the world with it; 3)
Use a known receiver for reference: i.e.,
find a signal such as WWV (2.5, 5, 10
*Figure reduced by 40% and 15 MHz) on your known receiver,
then “zero-beat” it with the DXer.
Figure Qty. Description Vendor This is done by placing the Dxer in
C-1 1 Capacitor, Trimmer, 3-40pf. OS, AES, RS, Dans full regeneration (squealing), and
C-2a,b 1 Capacitor, Variable, Dual Gang, 340/80pf. (approx.) OS, AES, Dans slowly tuning until you hear the
C-3 1 Capacitor, Variable, 25pf. (approx.) OS, AES, Dans squeal in your known set. In doing
C-4 1 Capacitor, Mica, 100pf., 100V. OS, AES, Dans this, you will get an idea where you
C-5 1 Capacitor, Mica, 470pf., 100V. OS, AES, Dans are in the band. Denote the set-
C-6,8,9 3 Capacitor, Mylar, 0.05uf., 100V. OS, AES, Dans, RS tings. Fully back-off the regenera-
C-7 1 Capacitor, Mylar, 0.005uf., 100V. OS, AES, Dans, RS tion control, then advance it until
L-1,2 50' Wire, Magnet, 22ga. OS, AES, Dans, RS you hear a “rush”, then re-tune the
" 3 Plug-in Coil Form Sets, 8-Pin Octal, 1-1/2" Dia. *PO set, etc. to locate a station. With
" 1 Socket, 8-Pin Octal OS, AES, Dans practice, you’ll soon learn this
L-3 1 Choke Coil, 2.5MHy. OS, AES, Dans technique; 4) If you like code or
IT-1 1 Transformer, Interstage, 1/3 Ratio *PO single sideband, locate a signal
R-1,4 2 Resistor, 2.2M., 1/2W-5% RS, OS, AES, Dans and then place the regeneration
R-2 1 Potentiometer, 50K, Linear, 1/2W., w/Switch RS, OS, AES, Dans
control into feedback (squealing),
R-3,5 2 Resistor, 10K., 1/2W-5% RS, OS, AES, Dans
then slowly tune with the band-
R-6 1 Resistor, 1K., 1/2W-5% RS, OS, AES, Dans
spread control until audio comes
V-1,2 2 Tube, 1T4 XSS
to clarity. This is a very tricky tech-
2 Socket, 7-Pin Miniature XSS
nique and takes lots of practice,
3 Knobs RS, OS, AES, Dans
Misc. Hardware items as per drawings RS, OS, AES, Dans
but it’s a blast! Have fun! Until
1 Baseboard, Any Knot-Free Wood, 6" x 8" x 3/4"Thk. LLY
next time…Mike.
1 Front Panel, Plywood, 6" x 8" x 1/8"Thk. LLY
1 Aluminum Foil, Front Panel Shield, 6" x 8" HH Note: See Page 12 for Coil #3
1 Power Supply, 1-1/2V., 45V., 90V-DC., XS-105 XSS, Suggested Figure 9b.
2 Batteries, 1-1/2V-DC., "C" or "D" Cells, Parallel LHW
10 Batteries, 9V-DC., Transistor-Type, Series LHW

Note:
*PO: Can be purchased from: M ike Peebles, Peebles Originals, 4416 NE
129th Ave, Vancouver, W A 98682. The set includes: 1) IT-1 Transformer &
Parts, for 3) Plug-in Coil sets, less wire. Cost: $20.00 in USA and
$40.00/Foreign. Check or M O in USA and Int'l M O for Foreign, accepted.
Checks held 10 days and other orders shipped the same week.

Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 4
 My fascination led me to purchase an old
Tektronix 575 curve tracer to study the
curves of iron pyrites (Figure 1), galena and
other detector materials that we normally
play around with to make crystal sets. The
575 is a vintage but great tool, because it
continuously shows the curve in real time as
you manually manipulate the samples. This
is what is needed in order to make observa-
tions while manually touching a piece of
wire to a piece of rock. I wanted to be able
to display both the positive and negative
portions of the curves simultaneously, and
so I had to modify the curve tracer in order
to do so.
Visable on the curve tracer (Figure 2) is a
negative resistance curve that could be
obtained from several different pieces of
iron pyrites (with much finicky adjusting).

IRON PYRITES NEGATIVE RESISTANCE OSCILLATOR

By Nyle Steiner

This experiment has been a very exciting experience for me,

as it represents the ability to build a simple homemade
active semiconductor device. It is almost like making your
own homemade transistor. This is the realization of a very
old and esoteric experiment so vaguely reported in a few
articles that I have often wondered if in fact it had actually Figure 2: Negative resistance can be seen in the reverse bias por-
been done. Even so, I have always had an extreme fascina- tion of curve. 2V/div. horiz. 2mA/div. vert. Curve tracer was
tion with those reports of being able to produce a continu- modified to apply ac to device.
ous wave RF signal from a crude semiconductor material
Not all pieces of iron pyrites seem to work. I found that the
kind with a lot of little crystal formations worked the best.
The fact that I just happened to have several working pieces
makes it appear that a working crystal is not all that rare. It
was nice to realize that this phenomenon was not just the
result of some fluky one-in-a-trillion find.

Figure 1: Iron Pyrites with #30 copper wire catwhisker.

back in the very early days of radio.

This oscillating crystal experiment was a sucessful attempt

to duplicate those done in the 1920's by W.H. Eccles,
Greenleaf W. Pickard and Oleg Losev. This experiment was Figure 3: Two types of negative resistance. Left, iron pyrites.
mentioned in past Xtal Set Society Newsletters, (January Right, tunnel diode.
2000 and May 2000).
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 5
As the curve tracer photo shows (Figure 2), the negative my voice on a nearby radio with a carbon microphone
resistance region is in the reverse bias portion of the curve placed in series with the battery supply. Just imagine the
at approximately -8 Volts and 8 mA. Some of the articles fun it was to be able to talk on the radio with an electrified
refer to this as being like a tunnel diode. It is true in the crystal set.
sense of having negative resistance, but it is in fact a differ-
ent type of negative resistance. This is OK, since both types Once a good piece of iron pyrites is selected, the curve trac-
of negative resistance can have the effect of gain, supplying er is not necessary. A method of indicating whether the cir-
enough energy to an LC circuit for it to become an oscilla- cuit is oscillating or not is the most important tool in mak-
tor. The negative resistance portion of the curve is obtained ing circuit adjustments.
when negative voltage is applied to the catwhisker.
The sole purpose of the diode and 50 microamp meter is to
I am not an expert on negative resistance, but I once read an be able to tell when the circuit is oscillating. The meter can
article many years ago that described how negative resist- only deflect when oscillation occurs, and this makes adjust-
ance is in two forms. I seem to recall them being a type S ment possible without the use of an oscilloscope. With an
and a type N (I don’t even remember for sure which is oscilloscope, no meter is necessary. The best way to get the
which). One type is found in a tunnel diode, and the other circuit going is to set the 1k pot to a midpoint and then
type is found here and in other devices such as a neon lamp, probe the catwhisker around the crystal until oscillation
a unijunction transistor and what I believe to be in the old ocurrs. The searching around the crystal is by far the most
carbon arc transmitters. Figure 3 shows how the two types critical part of the adjustment. If nothing happens, the pot
of negative resistance curves are possible. The negative level is raised a bit and searching on the crystal continues.
resistance seen on the curve tracer (Figure 2) is upside down The ranges on the pot that work are fairly wide in relation
with respect to that shown in the left part of Figure 3 so that to the complete range of the pot. This puts most of the bur-
both the positive and negative portions of the curve can be den of adjustment on simply searching the crystal. Use just
the oscillation indicator for adjusting. Get the
circuit oscillating, and then tune it to a select-
ed frequency on a nearby radio. Trying to
adjust by listening to the the radio is futile,
because you have to search the crystal for
each of many many different tunings as well
as for each of many different pot settings.
You can imagine how many combinations
would have to be tried.

I found it extremely difficult to get steady

oscillations with conventional type cat-
whiskers. I tried a simple idea that I call the
Tone Arm catwhisker because of its resem-
Figure 4: Schematic of broadcast band Iron Pyrites negative resistance oscillator.
blance to the tone arm of a phonograph. With
Carbon mike enables AM broadcast to nearby AM radio. it, I can often obtain steady oscillations that
last indefinite periods of time (several min-
displayed. utes anyway). It is made by soldering a fine #30 piece of
copper wire about 1/2 inch long, pointing down, to the end
The circuit shown (Figure 4) will easily produce a continu- of a piece of thick wire that is made to balance near the
ous wave signal in the broadcast band. It seemed difficult middle as shown in Figure 5. Pressure can be adjusted by
to get it to operate above 2 mHz, but it was easy to get it sliding a small weight along the wire if necessary. This cat-
running at anything below that, including audio frequencies. whisker also worked very well when used with a normal
It seems to prefer certain LC ratios better than others. In the crystal set. To connect the iron pyrites, several turns of bare
case of the broadcast band, a 365pF variable capacitor #18 copper wire were wrapped around it and twisted tight.
worked well with a 190 µH coil (100 turns on a TP roller). I have always found this kind ofarrangement to be as good
as anything. It has never seemed that casting in molten
When adjusting the 1k pot, I could find a range where the metal, etc., is at all necessary for any of the crystals I have
oscillation amplitude would vary with the voltage from the ever experimented with. Another copper wire over the crys-
pot. This suggested the possibility of voice amplitude mod- tal and wrapped around a couple of screws in the board
ulation with a carbon microphone. I was indeed able to hear works well for mounting the crystal.
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 6
 Figure 5: Iron Pyrites Oscillator Board and nearby radio.
Note the “Tone Arm” catwhisker.

Figure 6: close up of “Tone Arm” catwhisker in contact with

iron pyrites.

mechanical or electrical, energy may accumulate from repetitive

Figure 7: Nyle’s improved Tone Arm catwhisker. A triangular
low levels of input energy recurring at the resonant frequency of
wire frame, a weighted base (with three felt bumpers on the bot-
the system. Also in a resonating system, energy continually trans-
tom) and hinges to allow the arm to move up and down easily.
fers from one form to another. In the case of a mechanical system,
such as a pendulum, energy is transferred between kinetic and
Do not sell your expensive radio just yet. This circuit is far
potential. When the pendulum reaches its highest position, it
from being a replacement. It is extremely finicky to adjust stops instantaneously as it reverses direction. At that instant, the
and doesn’t stay in adjustment well. However, I can usual- system’s energy is entirely potential. At the lowest level of the
ly find a setting where the circuit can be run for a number of pendulum’s swing, velocity is maximum, potential energy is zero
minutes while I walk away and do something else. The and the pendulum energy is entirely kinetic. At all other positions
biggest feature this circuit has to offer is the thrill of watch- the pendulum energy is the summation of these two kinds of ener-
ing it run. gy. In the electrical resonant system, energy is transferred between
electrical energy, which is stored in the capacitor, and magnetic
energy which is stored in the inductor. In any driven resonant sys-
On Q tem, energy continues to build up until it reaches a steady state
By Bill Simes condition where system losses dissipate energy at the rate energy
is being added. A resonant system also tends to remain in oscilla-
Here are some thoughts, some calculations, some empirical meas- tion after the source of excitation is removed. In that case the
urements and even a bit of discourse on coil Q as it may apply to amplitude of oscillation diminishes exponentially at a time rate
the crystal set. Said to be the quality factor of a coil, Q is a ratio determined by losses in the system. In any resonant system, the
of like parameters. i.e. Ohms divided by Ohms, energy divided by two kinds of energy will vary sinusoidally and out of phase with
energy, etc. Since a unit divided by itself is one, Q remains a one another. With these conditions in mind, let’s examine the RLC
parameter without dimension. In a resonant system, whether it be
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 7
 circuit shown in Fig. 1.
ω 0 (energy. stored .in. the. circuit ) ω 0U
Q= =
The inductance, L, is average. power . loss WL
dimensioned in henries, (Equation 3)
the capacitor, C, in
From Eq. 3 comes another expression for WL, i.e.
farads and the series
resistor, Rs, in ohms. ω 0U
Let’s assume a condi-
WL =
Q
tion of oscillation
and on substituting this in Eq 2,
immediately after the
driving signal is inter- ω0
rupted. If the losses α=
(designated by Rs) are
2Q
small, then the decay
thus expressing the exponential decay of the damped oscillations
Figure 1: Schematic rate will be exponential
in terms of Q. If energy loss over only a few cycles is neglected,
and proportional to the
then the current in Eq. 1 for those few cycles may be expressed
amplitude of oscillation. Also, for a small number of cycles, the
simply as
change in amplitude will be relatively small. In keeping with
those conditions, the circuit current, I, can be expressed in the I = A cos ω 0 t
form
making A the peak value of the current at the instant when
(Equation 1)
where ω0 is the angular resonant frequen- ω0 t = 0
I = Ae −αt cos ω 0t cy in radians per second which is 2π times
Electrical power can always be expressed as I2R using the rms
the resonant frequency, f (in cycles per second). Most any physics value of the current. The rms value of sinusoidal current of peak
text will derive the energy in joules, U, stored in an inductor to be value A is

L(I max ) so without repeating its derivation here,

1 2
U = A The average power loss in the circuit series resistance, R ,
s
2 please accept this one on faith, or consult a 2 in Fig. 1 is then
physics text. When t=0, both cos0 and e-αt
and have the value of 1, making A the value for I in Eq. 1 at that Rs A 2
instant. The current, I, is then at its maximum value, and the ener- WL = Combining this expression for WL with that of
gy stored in the inductance becomes the total energy in the circuit. 2
At that instant, circuit energy in joules can be expressed as Eq. 3, yields the familiar expression

1 2 −αt ω0 L
U= LA e Q=
2 Rs in which Rs is again the circuit series resistance in
Fig. 1. All losses in the circuit are manifest in Rs.
The time rate of change for the energy is then That would include the winding wire resistance corrected for skin
effect, any dielectric losses in the circuit, any interconnecting
dU LA 2 − 2αt
= −2α e = −2αU resistance, any radiation losses, and any other circuit loading. The
dt 2 dU combination of these rather elusive losses may make the expres-
sion of greater practical value for evaluating Rs once Q is deter-
By definition, power is energy per unit time, so dt mined by other means. Also, keep in mind that both Q and Rs will
then expresses the power being consumed in the process of damp- vary with frequency.
ing the oscillations. Call the magnitude of this power, WL.
Then Consider now the same RLC circuit when it is driven by an exter-
WL nal resonant sinusoidal source loosely coupled to the inductor.
W L = 2αU and
α= (Equation 2)
The circuit reactance is the algebraic sum of its capacitive and
2U inductave reactances. The circuit is resonant when the magnitudes
In the case for damped oscillations, Q can be defined as the ratio of these two reactances are equal. In other words,
of energy stored in the circuit to the energy dissipated during each
cycle. That is 1 1
ω0 L = then ω0 2 =
Q = energy.stored.in.the.circuit ω0C LC
energy.lost.each.cycle

If both numerator and denominator are now multiplied by ω0, the 1

yielding the familiar ω0 =
ratio remains dimensionless and Q can be expressed as LC
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 8
As explained earlier, the energy in the circuit will be stored entire- Another relationship of possible interest is the ratio of
ly in the inductor as
R0 ω0 L ω0 L
1 2 Q= then Rs =
LI Rs . Since Rs Q
2 at one extreme of the cycle and stored entirely in the
capacitor as and on using this for the value of the denominator
and using Eq. 4 for the value of the numerator and recalling that
1
CV 2 at the other extreme. At any other point in time, both I 1 R0
2 = Q2
and V will be at less than their peak values. Still the sum
ω0 = it can be shown that
of the two energies remains essentially constant over a short time LC Rs
span. Let’s choose a point in time when all the energy is stored in
the capacitor. Then if we multiply our expression for electrical Assuming R0 can be determined more accurately than Rs, this
energy by relationship would be useful for calculating Rs.
ω0 1
ω 0 and substitute for ω0 At this point I went to the basement to measure some of the
LC parameters discussed above. For the inductor, L in Fig. 1, I used
an ancient coil (circa 1920) with 57 turns of dcc 1/8-inch square
then in the numerator we can write copper bus wire wound on a 5-inch diameter form. Its inductance
measured 122 microHenries with a distributed capacity of 75.5
1 1 V2 C
U = CV 2 * = pF. The capacitor, C, was of similar vintage with a maximum
2 ω0 LC 2ω 0 L capacity of 742 pF. For instrumentation, the signal source was a
home brew Hartley oscillator. This was connected to a Mattco
From Eq. 3, it was shown that model 711 counter with 5-digit readout to give an accurate fre-
ω 0U quency measurement. A Telequipment DM64 oscilloscope was
WL = used as a high impedance voltage indicator. Vertical deflection
Q was assumed to be a linear function of voltage, and this was used
to compare relative voltage amplitudes rather than to actually
Then using the above expression for U in the expression for WL , quantify voltages. Included also in the instrumentation collection
the power loss at resonance becomes was a Radio Shack 22-181A digital multimeter for resistance
measurement. At a resonant frequencies near 0.71 mHz, coil Q
V2 C
WL = was measured to be 165, as calculated be dividing the resonant
2Q L frequency by the frequency band width (difference between the
frequencies each side of resonance that gave a deflection 0.71 of
An external source applying a sinusoidal voltage across C would that at resonance). For all of these measurements, L was excited
then see a rather high resistance, R0, at resonance. For the system by positioning it a few inches from the Hartley oscillator coil. To
to maintain its steady-state equilibrium that source would have to estimate R0, a 1-megaohm pot with short leads was connected
supply all of the power lost by the system. In which case across the capacitor. With one of these pot leads disconnected, the
V2 circuit was peaked at resonance and the scope deflection meas-
WL = ured. The pot was then reconnected across C, the tuning capacitor
2 R0 where V is now the peak value of the sinusoidal was tweaked for maximum deflection, and the pot adjusted for a
driving voltage across C. On equating our two scope deflection half that measured at no load. The resistance of
expressions for WL and solving for Ro, it is seen that the pot at this setting was then measured to provide the estimated
value of R0 at the frequency of the test. Measurements for R0 near
L
R0 = Q (Equation 4)
0.7 mhz were of the order 85 k to 90 k Ohms.
C
Let’s now analyze our data for possible application to crystal sets.
This equation may be useful to the crystal set enthusiast. First, it In general, crystal sets depend on tuned circuits, in one form or
quantifies the impedance that must be matched to transfer maxi- another, to separate and enhance incoming signals. Unlike radio
mum power to the load. Since at resonance, reactances cancel one circuits that feed tuned signal voltage to the near infinite imped-
another the resonant impedance is purely resistive. Secondly, it ance of a detector or amplifier, the crystal set is a passive device
suggests another approach to measuring Q. On solving Eq. 4 for that must exact all of its power from the tuned signal. This brings
Q it is seen that with it some bad news. Even when the crystal set circuit is
matched for maximum power transfer to the headphones, only a
R0 C part of that signal power is transferable. As an analogy, consider a
Q= = R0 conventional battery. The battery has an internal resistance, call it
L L
R, and a no-load voltage, call it VNL. If the battery is shorted, the
C power dissipated is VNL 2/R . This is the maximum power the bat-
tery can deliver. Of course this power is not delivered to an exter-

Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 9
nal load. Instead it is dissipated internally as heat. It is not too dif- the two coils are wired in series with each other so that only one
ficult to show that maximum power is transferred to an external end of each coil is available to the outside world. Refer to Figure
load when the load resistance equals the battery’s internal resist- 1 for the schematic diagram. As can be seen, the outside world
ance. The load voltage is then VNL /2 leaving the power delivered can be connected to terminals 1 and 2. So what does this won-
to the load (VNL /2)2 /R or VNL 2 /4R. So even under conditions derful widget do that is so astounding? As you turn the shaft over
180 degrees of rotation, the inductance will smoothly change over
of maximum power transfer, only ¼ of the battery power capabil- about a three to one range. This means no taps are used to change
ity can be delivered to an external load. As in the battery analogy, the inductance by switching between taps with its attendant jumps
Eq. 4 implies that maximum power will be delivered to a load in inductance. If you need a precise inductance to, say, cancel the
resistance equal to that of R0. Paralleling R0 with a load of equal antenna capacitive reactance, here’s just the ticket. What’s anten-
resistance produces a combined resistance to R0/2 which is now in na capacitive reactance? That’s another subject – Stick with me
effect the new value for R0. L and C remain unchanged in Eq. 4, on this one.
so Q must be reduced to half its no-load value to satisfy the equa-
tion. When Q is expressed as the resonant frequency divided by In my research I found plenty
the bandwidth, it is clear that for a given resonant frequency the of information about variome-
bandwidth must be doubled when Q is halved. This shows that ters and lots of pictures, illus-
crystal set selectivity will be sacrificed as sensitivity is maxi- trations, and articles about
mized. Eq. 4 offers another possibility. On solving Eq. 4 for Q it their construction and use, but
is seen that I have never found much
information about the actual
C inductances. This is where I
Q = R0 gave every consideration to
L the mechanical and electrical
From the basement data, with resonance near 0.71 mHz (w=4.46 characteristics of the variome-
E6), Q was measured to be 164 and 165 using Q=f0/∆f . Pot resist- ter and the calculations
ance measurements for estimating R0 at this frequency were 85 k required to obtain a satisfactory result…and gave it my best guess.
The one I am about to describe varies from 225 to 625 microhen-
and 90 k. Knowing the value of L to be 122 uH and using the rela- ries.
tionship ,
Construction: I wished to make this variometer out of parts that
1 C+C0 was calculated to be 411.9 pF. (this value was
LC = 2 are readily obtainable to just about anyone. With this in mind I
ω also confirmed by the variable capacitor calibration visited our local fabric store. If you would take a look at the paper
data and the previously determined value of C0 for tubes that ribbons and laces are wound on, you will notice some
the inductor). Using measured values of R0 and the known val- that are 3-1/4 inch diameter and about 2 inches long – just the
ues for C and L in the expression for Q above, Q was found to be right size for the outer coil of the variometer. If you ask nice they
156 when R0=85 k and 165 when R0=90 k. I was pleasantly sur- will probably be glad to give you some. The other coil is made
prised with the close agreement among Q values evaluated using from a 2-1/4 inch diameter mailing tube or from one of the tubes
these two methods of measurement, considering the accuracy that hold plotter paper that reproduction outfit’s use. Look under
and/or precision uncertainty of my instrumentation. “copies and reproducing” in the phone book. Of the smaller tube
you will need a 2 inch length. The other items you will need are
Hopefully, a crystal set enthusiast will find here something of use two rubber grommets that will fit snugly over the shaft, consisting
and/or of interest. In any event, to all readers I extend a heart felt of 6 inches of ¼ inch diameter wood dowel. You will also require
Thank Q! some #24 and #28 enameled wire.

Coil Form Construction:

The two coils need to be wound in slightly different fashion than
Various Notes on the Variometer normal. As the shaft extends through both of the coil forms you
by Dan Petersen, WA6ΟIL need to provide a space in the center of the form for the shaft.
Please refer to Figure 2 for the specifics on the coils. Before wind-
The Variometer: The very name conjures up images of Boris ing however, you need to prepare the coil forms by drilling the
Karloff movies (Igor! Turn the Variometer to MAXIMUM!!!) or shaft holes. To get them directly opposite one another do the fol-
perhaps Edison’s laboratory. While it won’t raise the dead, the lowing: Take a sheet of typing paper and cut a 1/2 inch wide strip
variometer is one of the oldest components used in the radio from along the long length of the paper. Now wrap the strip
industry and probably WAS in Edison’s inventory. It is also an around the body of the coil form and put a mark on the strip where
interesting gadget that can still find use in today’s crystal radio. the end overlaps the strip. Remove the strip and cut the strip
across at the mark. Fold the strip in half. Cut the strip at the fold.
The variometer is a rather simple device consisting of two coils,
The remaining strips each are ½ the circumference of the coil
one smaller and placed inside the other. A shaft extends through
form. Place the strip back on the coil form and mark where the
the two coils, enabling the operator to rotate the smaller coil with-
ends of the strip lie. Put the marks roughly halfway between the
in the larger. The variometer is called a “two-terminal” device–
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 10
ends of the coil. Measure between the ends of the coil form and
make another mark halfway from each end. Where the two lines
meet is where you want to drill the holes. Use a 1/4 inch drill bit
at high speed and use light pressure. Also, have a piece of wood
behind where you are drilling for the bit to bore into when it goes
through the form.

Winding the coils:

As stated before, the coils need to have a 0.5 inch gap in the cen-
ter of the coil with half of the windings on each side. If you use
the coil forms specified you may start the winding 0.125 inch (1/8
inch) in from the end of both coils. On the primary, wind 25 turns
of #24 enameled wire close-wound on the form, then over ½ turn
move the wire across the 0.5 inch gap and wind 25 more turns. On
the secondary, wind 30 turns of #28, half-turn over the gap, then
30 more turns. A couple coats of varnish suffice to secure the coil
on the form. I usually paint my coil forms black before winding
them. Once wound and varnished they look really vintage.

in the shaft and down a hole drilled along the length of the shaft.
This hole only needs to be 1/16 inch diameter and needs to extend
far enough to get inside the secondary form. This is a rather nifty
way to get the secondary wires out to the outside world. The coil
assembly is mounted to the base using a wood block affixed to the
coil, then screwed to the base. On mine I have the shaft pointing
up at a 45-degree angle to place the adjustment knob at a conven-
ient angle. I mounted a dial on mine by epoxying two small wood
blocks on each side of the shaft, then mounting the dial plate using
small brass flathead wood screws.

Connections:
The connections to make the thing work are quite simple. You will
note that the primary is wound with #24 wire and the rotating sec-
ondary is wound with #28 wire. Pick out one of the #24 and one
of the #28 wires, scrape the insulation off the ends, twist them
together and then solder the connection. The remaining two wires
can then be connected to binding posts. On my unit, I have
brought out all four wires to binding posts. With the posts in a line
as shown in Figure 4 the wire connections are: Large wire-small
Final Coil Assembly:
wire-large wire-small wire. I then made a brass shorting bar to go
Now comes the time to put the thing together. Prepare a shaft from
between the two middle binding posts. Removing the shorting bar
a 6 inch piece of 1/4 inch wood dowel. You will also need the two
makes the unit a “variocoupler”. This differs from the variometer,
rubber grommets that will fit snugly over the shaft. Take one
as it is now two distinct inductances with variable coupling
grommet and force it onto the shaft, pushing it about 2 inch down
between them. Frankly, I have never needed to use it in the vario-
the length. Now feed the long part of the shaft into the primary on
coupler mode.
the side farthest from where the windings end. Push it in until the
shaft sticks about 1/4 inch inside the primary. Set the secondary
Theory of Operation:
coil inside the primary and push the shaft into the secondary shaft
What you have done is to connect the two coils in series. The the-
hole on the side farthest from the windings end. Continue pushing
ory of operation is that you have two coils connected in series
the shaft through until the grommet comes up against the primary
AND they are heavily coupled to one another. Normally, two
coil. Force the other grommet onto the other end of the shaft until
inductors that are physically in series and that are NOT inductive-
it comes up to the primary. You next center the secondary inside
ly coupled will exhibit the sum of their two inductances. If you
the primary and using epoxy or other suitable glue, secure the sec-
start to inductively couple them, the magnetic fields will start to
ondary to the shaft. You must NOT glue the primary to the shaft.
interact, which will change the total inductance. In the case of the
That kind of negates the whole point of having a rotating shaft!
variometer the secondary coil can be rotated through 180 degrees.
You will note in Figure 3 that the secondary wires go into a hole
As you do this, the coils will first “boost” each other, creating a
Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 11
high inductance. As the secondary rotates through 90 degrees (or
at a right-angle to the primary, there is minimal coupling, and the
inductance is the sum of the two coils. Continuing on, the coil
fields start to “buck” one another, causing the inductance to drop
to the minimum value. The change is not linear. It flattens out
Secrets of Homebuilt Regenerative Receivers By
near the ends of rotation. Nonetheless, the change in inductance is
C.F. “Rock” Rockey. All you need are a couple of vacuum tubes
at about a three to one ratio.
or transistors and not much more than a handful of other parts to
build a simple, but hot performing regenerative receiver. With it
So What’s It Good For?
you can cover the short-wave bands, and listen in on foreign
The variometer saw use in the early days as an alternative to coil-
broadcasts, amateur communications, ships at sea, secret spy
and-slider type tuners. This of course would work well if you had
transmitters, and much more. These amazing radios may have
only one station within range. In today’s world, making a crystal
simple circuits, but the old pro's knew the special secrets needed
set with a variometer tuner is fun from the vintage aspect but is
to make them perform. This book has all the little things that are
about the worst design for trying to separate stations. Another use
left out of other books on building sets, but it does not have
for the variometer is as a regeneration control. Envision a regen
detailed instructions. These secrets set you up for success. 8 x 5½
rig using a “throttle” variable capacitor for a regeneration control.
paperback, 127 pp. Cat # LSH $9.95
Remove the variable and connect the variometer between the tick-
ler coil and the headphones. If the values are right, it will control RADIOS THAT WORK FOR FREE*****
the regeneration just as well as the throttle capacitor. Where it by K.E. Edwards. Originally published in 1977, this book has
finds the most use these days, however, is in the antenna tuner. been one of the most popular publications about crystal sets. Great
Since an electrically short antenna “looks like” a capacitive load for beginners or those needing a “refresh” of the basics. More
to your set, the variometer is just the ticket for tuning this capaci- than half of the book is introductory and includes a discussion of
tance out of the circuit. Here’s an example. I recently took part in crystal set basics, with separate chapters on antennas, detectors,
a crystal radio DX contest. For a set I used an Australian design phones, coils, and capacitors. Also included is information on
“Mystery” set with the variometer connected in series with the schematics, layout, and soldering. The last third of the book
antenna lead-in. I picked up over twenty stations in seven states includes 3 crystal set projects with parts lists & directions, 128
(and that’s BIG western states), two provinces and Mexico. pages. Cat# HRF $12.95
Farthest DX? WOAI in San Antonio, Texas, a distance of over
1700 miles. The variometer made a vast difference in the effec- Twinplex Regenerative Receiver
tiveness of my antenna. So give ‘er a go. -Dan Build 3 different hot performing shortwave regenerative
receivers! Lindsay shows you how step-by-step. Great directions,
photos, and figures. 1934 Doerle Twinplex, 6SL7 Twinplex &
Solid-State Twinplex. 5x8 paperback, 63 pp. Cat# LTR $9.95

How to Build Your 1st Vacuum Tube Regenerative

Receiver, by TJ Lindsay. Build a great little set from salvaged
material, lots of info and super step by step instructions. 5½ x 8 ½
paper, 127 pp Cat# LVT $9.95

Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 12
Xtal Society Books Your July 2001
Newsletter is Enclosed
www.midnightscience.com
B A C K I S S U E S OF T H E X T A L S ET S O C I E T Y N E W S L E T T E R
VOLUME I & II Don’t miss out on these great Originals! Now combined
Crystal Set Projects: as one book, the original 12 issues still hold their own. They include a com-
15 Radio Projects You Can Build plete set of plans for a “Modern Day Crystal Set,” Why did the sets of the
Crystal Set Projects is a collection of 1920’s work anyway? Crystal sets and wireless, 1905-1928. Matching
radio projects that won a building con- your antenna and set for maximum signal reception. The Lead Pencil
test run by the Society. Included are Detector! Detector Biasing for improved sensitivity. Double-tuned circuit
step-by-step instructions so you can crystal sets. The Universal Crystal Set. FM crystal sets? The electrolytic
build and design your own Xtal sets no detector. The coherer revisited. The Miller ‘595’ Tuner. 8½x11, spiral bind-
matter what your background in elec- ing, 80 pgs. Cat# XV2 $18.95
tronics. The projects are of various VOLUME III See description bottom left. Cat# XV3 $10.95
designs and difficulty so that everyone VOLUME IV Great stuff from 1994 on measuring coil capacitance, two
can learn something. “Crystal set cir- building projects using Quaker Oats boxes, broadcast and short-wave,
cuits have been regularly published in how to make home-brew headphones and curve tracers, how crystal ear-
the hobby press since the dawn of phones work, and a description and schematic of 10 crystal sets. 85 pgs.
radio. But the Xtal Set Society’s new project book covers more Cat# XV4 $10.95
electronic and mechanical variations of this ever-popular receiver CRYSTAL SETS: VOLUME V These reprints of the Society newsletter
than I have ever seen in one place. You’ll find hi tech and low tech from 1995 are a lot of fun. They include a three part article on the design
versions, vintage and modern versions, sets with loop antennas and of unpowered AM receivers made from rocks, including plans for building
short-wave bands. The book is as much fun to read as to build from, test equipment such as an impedance meter and a Q meter. Also covered
but I defy anyone to browse this infectious publication for long is a radio outfit in a headset, a Marconi type 107-A tuner, the matching
without experiencing an uncontrollable urge to break out the sol- secret, and a great ground-noise powered receiver. Get a copy for your-
dering iron and double-cotton-covered wire!” —Marc Ellis, Editor, self or for a fellow radio friend! 8½ by 5½ paper, 88 pgs. Cat# XV5 $10.95
The Old-Timer’s Bulletin of the AWA; Get yourself a copy! 6 x 9 VOLUME VI & VII See description on order form. Cat# XV7 $15.95
paperbk, 160 pgs. Cat# CSP 14.95 VOLUME VIII See description on order form. Cat# XV8 $15.95
CRYSTAL RADIO: HISTORY, FUNDAMENTALS, AND 1934 Official Shortwave Radio Manual Edited by Hugo
Gernsback & H.W. Secor. Build simple,
DESIGN




Written by a
long time member of the XSS, Mr. Phil high-perfomance old time shortwave radios!
Kinzie, this book chronicles the fascinating All of the secrets are here: the circuit dia-
history and development of the crystal grams, parts layout, coil specifications, con-
detector. Starting with the discovery of struction details, operation hints, and more.
solid-state rectification and then through Back in the 20’s and 30’s the only low-cost
the development of the crystal detector the way of listening in on the newly discovered
reader learns about great inventors such as and fascinating short-wave radio frequen-
Pickard, Braun, Dunwoody, and others. cies was to build a set. This is a compilation
Radio fundamentals such as antennas, of construction articles from “Short Wave
ground, lightning protection, tuned circuits, and detection are cov- Craft” magazine. 8½x11, paperback 259 pages. Cat# LSW $15.95
ered for the beginner. The unending compromise between selectiv- SECRETS OF RF CIRCUIT DESIGN 3rd edition
ity and sensitivity is discussed. Topics such as the use of multi- by Joseph J. Carr The best ways to design, build, and test today’s
tuned circuits and wave traps follow for the serious experimenter. radio frequency (RF) circuits can be found in this very thorough
Great background for any radio builder. 8½x5½ paperback, 124 guide. It’s filled with projects and experiments that make it easy to
pgs. Cat# XCR $11.95 apply RF principles to real life applications. Parts lists and compo-
nent sources are listed for every project; building radio receiver cir-
THE CRYSTAL SET HANDBOOK cuits, RF bridges, and amplifiers. The book also covers selecting
by Phil Anderson. There is nothing else out there like this and repairing variable capacitors, designing wind inductor coils for
handbook. It takes the reader beyond the basics and dis- radio circuits, and constructing and grounding simple wire anten-
cusses the math and mechanisms behind the mystery of nas. If you want to learn more about RF circuits this is a must have.
the crystal set. This book is written for crystal set enthusi- 7½x9 paperback, 568 pgs. Cat# MSR $39.95
asts, radio amateurs, first-time radio experimenters, and
electronics students. Contents include an introduction to Theory, Design, and Operation of Crystal Receivers, by K.G. Kott,
the crystal set with a simple oat box project, formulas for W8ROG. Originally published in 1953 by Mr. Kott. Recently his daugh-
coil inductance and coil Q, a procedure for measuring coil ter Nancy Kott, WZ8C found it in her father’s attic and reprinted it. With
capacitance, introductory and advanced chapters on L-C hand typed pages and nicely done hand drawings, Kott takes the reader
circuit matching, and Volume III of the Society Newsletter from basic electronic theory, to capacitors, antennas, grounds, coil wind-
(issues 13-15). 8x5½ paper, 133 pp Cat# XV3 $11.95 ings and coil design including how many turns & wire diameter, coupled cir-
cuits, detectors, and headsets. Booklet, 8x11, 66pp.Cat# KTD $11.95
Xtal Set Society  PO Box 1625, Norman, OK 73070-1625  (800) 927-1
1771  xtalset@midnightscience.com
www.midnightscience.com
 THE XTAL SET SOCIETY The AM/SW XS-1101 Crystal
PO Box 1625, Norman, OK 73070-1625 Radio Kit Our radio receives both
1-800-927-1771 order line broadcast and shortwave, and includes
two spider-web coils that are variable to
e-mail: xtalset@midnightscience.com each other. Also included are a 365pf
We are dedicated to once again building and experimenting variable capacitor, diode, and all the nuts,
with radio electronics, often—but not always—through the use of bolts, clips, knobs, and wire you’ll need
the crystal set, the basis for most modern day radio apparatus. This (antenna and earphone not included).
newsletter helps support our goal of producing excellent quality The overall range of the radio is 550kHz
technical books that encourage learning and building. To join the to 8.0mHz, depending on your antenna,
society and receive one year of the bi-monthly newsletter, remit ground, and local conditions. If you live
$12.95 to The Xtal Set Society. Canadians, please remit US $14.00. near a very powerful station the short-
Outside the US and Canada please remit US $19.00. wave may be difficult for you, but the
Please send articles and correspondence to the above address. broadcast band is very selective. We
NOTE: Unless otherwise stated, The Society assumes that the mate- tested the set here in St. Louis and had
rial you supply is fit for print (free of copyright or other infringe- great results with both AM and short-
ments) and that by your submittal you have given us your permis- wave. The clips for the detector are a nice touch for experimenters;
sion to print the material without restriction. you can attach whatever detectors you’d like to try! It even has an
President & Editor Emeritus–Philip N. Anderson, W∅XI optional, very nice wooden cabinet kit if you want to give the set a
Editor & Crystal Queen–Rebecca, xtalset@midnightscience.com finished look. The cabinet is unfinished pine and unassembled.
Managing Editor–Mike Peebles, peeblesorig@uswest.net XS-101, 4½ x 4½ x 7¾, Cat# XS101 $29.95
Contributing Editor–William Simes, W∅IZC@kcnet.com Optional cabinet, XS-201, 4¾ x 4¾ x 9¼. Cat# XS201 $16.95
Contributing Editor-Dan Petersen, petersen@worldaccessnet.com THE BOY MECHANIC, VOLUMES 1, 2 & 3
Technical Advisor–Larry Pizzella, WR6K, larryap@ix.netcom.com Compiled by H.H. Windsor, reprints of the 1913, 1915, and 1919
Technical Advisor–Joseph Cooper, VE3FMQ editions. Great drawings and just plain fun to read. Here are some
examples: “700 Things for Boys to Do. How to construct wireless
outfits, boats, camp equipment, aerial gliders, self-propelled vehi-
RADIO for the Millions cles, engines, motors, electrical apparatus, cameras and hundreds of
With over 50 different radio plans, this reprint other things which delight every boy.” 5½ x 8½ paperbk, 469 pgs ea
from the 1945 Popular Science Monthly is Cat# LB1 / LB2 / LB3 $18.95 each
packed with ideas. One to four tubers, TRF, Henley’s 222 Radio Circuit Designs
Superhets, you name it! Each project includes Every imaginable schematic from crystal sets to big multi-tube
photographs, parts list, and a schematic - not a lot 1923 receivers & transmitters. A master reference of early radio cir-
of detailed instructions, but complete plans. It’s cuits for the collector & builder. Lots of schematics! 5x8 paper-
a great book full of tube radio designs for the pack. Cat# LH2 $11.95
experimenter. 6x9 paperback, 192 pgs. Cat# LRM $11.95 The EASY Wire Antenna Handbook by Dave Ingram,
The XS102 Crystal Radio Kit! K4TWJ. This book has been around for some time, but it is still one of the
Perfect for parents, grandparents, best antenna books available. Although Dave is writing for Hams, there is
and teachers to build with kids! great info for everybody. It is full of ready-to-use designs and dimensions
Also a super starter kit for the on both “basic” and “gain” antennas. Info on hidden and disguised anten-
beginning adult builder! Includes nas, tuners and baluns, SWR meters, noise bridges, and antenna tuners.
small coil form, wire, slider 8x10 paperback, 110 pages. Cat# CEW $10.95
assembly, capacitors, and diode. The AM/SW XS-104 One-Tube Regenerative
Easy parts Simple in design but great on performance, our kit has basic,
layout guide provided for kids. Excellent per- vario-coupler regeneration control. You add an ordinary saltbox, a
formance for such a simple but elegant classic 1T4 tube (available from the XSS; see below) and a 1.5/45V DC
slider. Earplug included. Cat# XS102 $17.95 source, and you're on your way to broadcast-band through 8.5
Quantity discounts available for teachers & MHz (approx.) listening. Though simple in design, this kit is rec-
scout leaders. ommended for those with some prior knowledge of kit building.
Radio-Craft: 50 Years of With a few simple tools and supplies the kit should go together
Radio In March of 1938 Radio-Craft maga- easily. The power supply requirements are simple: one C or D cell
zine commemorated the 50th anniversary of radio with a special and five 9V-transistor batteries in series will work fine. We have put togeth-
“Jubilee Souvenir” issue, now highly sought after by collectors. Its er a nice and neat way to handle this supply in our other new kit, the XS-
look back at the first 5 decades of radio is priceless, featuring arti- 105 A-B battery supply. Both kits also fit our standard XS-201 cabinet kit.
cles on the beginning of commercial broadcasting, technical devel- For short wave listening, it is highly recommended that you use an anten-
opments in the evolution of the home radio receiver & the famous na tuner, such as the XS-103 kit. Stations ordinarily missed will be greatly
Hugo Gernsback predictions of what the future of electronics would enhanced with the XS-104/XS-103 combination. Cat# XS104 $29.95
bring. 8½x11, paper, 143 pgs. Cat# SRC $15.95 1T4 Tube for the XS104 Kit Cat# 1T4 $2.95

Xtal Set Society   (800) 927-1

PO Box 1625, Norman, OK 73070-1625 1771  xtalset@midnightscience.com
www.midnightscience.com
OUR COMPLETE CATALOG ON-LINE AT WWW.MIDNIGHTSCIENCE.COM The Voice of the Crystal: How to Build Working
Crystal Clear Volume I & Volume II Cat# SC1 / SC2 (price ea) $29.95 Radio Receiver Components Entirely From Scratch by Peter
Make a Neutrodyne Receiver 1924 reprint Cat# LNR $ 6.95 Friedrichs. Crystal radio construction often means purchasing elec-
1937 Sylvania Tube Manual Cat# LST $12.95 tronic components. Not anymore with this super new Xtal book!
Homemade Lightning: Creative Experiments in Electricity Cat# MHL $19.95 Friedrichs, an XSS member, reveals how to construct all of the parts
Teach Yourself Electricity and Electronics Cat# MTY $34.95 from scratch. Basic theory and analysis is combined with dozens of
Troubleshooting & Repairing Consumer Electronics Cat# MTR $24.95 examples of historical practice, work by contemporary experi-
100 Amazing Make-It-Yourself Science Fair Projects Cat#SAM $12.95 menters, and construction details. Inside are plans for 3 different
Robot Builder’s Bonanza:99 Inexpensive Robotics ProjectsCat# MRB $18.95 homemade headphones, including one fabricated from cigarette
Oscilloscopes and Antique Radios Cat# ROA $ 9.95 lighter parts. Also included are detectors, fixed capacitors, and a
33 Simple Weekend Projects Cat# C33 $15.95 rotary variable condenser. Plus there are coil plans for single layer,
The Complete Shortwave Listener’s Handbook Cat# MSL $29.95 spider web, baskets, and a precision double-slider. Throughout, the
Simple Weather Experiments w/ Everyday Materials Cat#SWE $5.95 author shares his thinking and practical experience, and includes
Behind the Front Panel: Design & Develop 1920’s RadiosCat#WBT $18.95 over 120 photos and hand-prepared illustrations. Superbly written,
XS103 Antenna Tuner/Trap Kit Cat# XS103 $39.95 and just plain fun to read. 6x9 paperbk, 185 pgs. Cat# FVC $14.95
XS105 A-B Battery Supply Kit (goes with XS104) Cat#XS105 $16.95
CRYSTAL SET BUILDING & MORE:
CRYSTAL SET LOOPERS A 3 VOLUME 6 & 7
TUBER & MORE: Volume 8 of the of the Society Newsletter. Build these fun
Society Newsletter It’s the best vol- projects: An FM Xtal Set, A Crystal Head-
ume yet! Build a Shortwave looper, a phone from a Cat Food Can, The Den Two
AM/SW 3 tuber, a Antenna Tuner /AM Crystal Radio, From Crystal Set to
Superhete, The Simple TRF Set, Flame
Trap, a Loop with a new twist, a
Detector for the Xtal Set, The Foxhole Set,
Frisbee crystal radio, a radio from a TRF Receiver Using the ZN414, WWII
deodorant stick, and find more fun Underground Xtal Radio, Capacitance of the
building ideas. Learn about biasing Parallel Plate Capacitor, How to Make a
effects on diode performance and crys- Double Crystal Receiver, A J-Fet Shortwave
tal detector experiments. Discover Regenerative Receiver. 6x9 paper, 168 pgs.
crystal set secrets from our members all over the world. 6x9 Cat#XV7 $15.95
paperback, 128 pp. Cat# XV8 $15.95

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The Xtal Set Society
10th Anniversary
Fan Mail for The Peebles Choice
The May issue turned out to be very popular. I
worked on the issue with the same goals as always,
but somehow it just turned out better. We would-
n’t have known it without the fan mail, which just
kept coming in. I’d like to take this space to honor
Crystal Earplug, tinned ends Cat#Ear $2.50 our Managing Editor, Mike Peebles, whose com-
Galena Crystals (mounted) Cat# XTAL $3.00 mittment to the Society has made a real difference.
Galena Crystals (raw) Cat# XTAR $3.00 Here is one of the letters we received. -Rebecca
Phospor Bronze Catswhisker Cat# XCAT $1.50
2000 Ohm Headsets - Call for availability “Dear XSS,
Diodes - 1N695 Cat# DIO .50 Just received the May issue of the Xtal Set Society
Fahnestock clips (25), 5/16 x 3/4 Cat#FC25 $5.25 Newsletter and enjoyed reading Mike’s feature
Brass binder post Cat# BBP $3.00 article ‘Coil Winding Primer.’ Lots of good solid
365 air variable capacitor, single gang Cat#365 fundamental technical info of benefit to the verter-
$10.95 an radio builder, as well as the best start for begin-
ners in their attempts to wind a servicable inductor.
THE ROCKET RADIO IS BACK! Mike’s wire gauges and coil form diameters and
Remember playing "Spy" with your spy pen number of turns is the most comprehensive I’ve ever
radio when you were a kid? This little seen! And, again, the illustrations which accompa-
Rocket Radio takes you back to those times nied Mike’s text were superior. Also enjoyed Dan
too, digging through the Cheerios box Petersen’s article ‘The Old Timer.’ The arrangement
hoping the radio was in there. Some bril- for adjusting the coupling between antenna coil and
liant marketer with gobs of mullah (not me,
the tuned coil was most interesting. I’ve never seen
ha.) had these great remakes of the original
1950's Rocket Radio made. It really works,
any other arrangement as clever as this old-timer...
but be realistic, you're not going to get and to think that it was Mike who discovered the
Radio Japan on it! Instead of the 1950's cache of 1920’s vintage commercial coils! Mike,
look, these are packaged for "kids." Get one for you and one fellow, you are good for America. I’m looking forward to the
for the kids! Cat# XRR $12.00 July issue, when hopefully we are treated to another project
by The Peebles Choice!” - Bob Ryan, Hemet, CA 
THE IMPOVERISHED RADIO EXPERIMENTER
by TJ Lindsay. Although we are all Xtal radio builders I Jeffrey Forrest, D.D.S., Livonia, MI. Jeff
know you guys are also secretly building tubes radios in has been a loyal member of the XSS - recent-
your basements. Admit it! And if you aren't you secretly ly he sent some photos of the radios he’s been
want to try it and don't know where to start, probably building along with new toothbrushes for the
intimidated about where to get those old tubes and sock- kids! Thanks Jeff, it is always fun getting
ets. TJ lists tube substitutions, using more modern stuff in your messages!
place of the expensive antiques, and they work just as well.
Also included is information on an inexpensive tube power
supply, grid-leak detectors, regenerative receivers, list of
old magazine references, tube numbering, and nice
schematics. Old time radio building for pennies. 5½ x 8½
booklet 48 pages. Cat# LRE $5.95

100 Amazing Make-It-Yourself Science Fair Projects

Imaginative projects to impress the science-fair judges, your teachers, and
your classmates! From electricity to ecology, plants to perception, light
waves to living creatures demonstrate properties and effects from all fields
of science. Each project uses readily available materials and includes
instructions & diagrams to ensure your success. 7x10 paper 224 pgs.
Cat # SAM $12.95

Your July 2001

Newsletter is Enclosed
Xtal Set Society   (800) 927-1
PO Box 1625, Norman, OK 73070-1625 1771  xtalset@midnightscience.com
www.midnightscience.com
365 pf Air Variable Capacitors
These little beauties are manufactured
especially for the XSS. Brand new caps:
single gang, 31 blade, .010-air-gap with
5/8” long tuning shaft, CCW rotation, and
slotted end rotor blades.
Cat# 365 $10.95

Dual Gang 365 pf Capacitors are now available, same as singles,

just two sections with trimmers. Cat# 365-2 $21.95

PLEASE NOTE *NEW PO BOX* FOR THE XSS

The Crystal Queen is moving to Oklahoma! No changes to the
Society at all...just a new PO Box. The 800# and website
remain the same...and as always Rebecca is still in charge!

The Xtal Set Society, PO Box 1625, Norman, OK 73070-1625

Copyright  2001, The Xtal Set Society. All Rights Reserved. Page 13