5.6. The Boxes
For all lovers of the electronics, the box
where their device is to be put is the famous “production weak link”. The
finished boxes are either impossible to purchase, or they can be bought but
their dimensions or shape is inappropriate, or they are too expensive, or...
In cases like this one should be quick-witted enough to find some
square-shaped box that is being used at household, or some packaging box or
similar. That is how it’s done in the “whole white world”. Two years ago, in
the famous electrotechnical magazine ETI TOP PROJECTS the article named “TIC
TAC RADIO” was printed, where a receiver with ZN414 that is placed in the
transparent plastic box of TIC TAC mints (In the abstract, it was written
that making this device serves well as an excuse for buying candies, which
is probably meant for the readers that are on a diet for aesthetic reasons).
However, the “finishing touch” is of great importance for everything. The
majority of your friends will be more impressed by a lovely box where the
receiver is placed, than the reproduction quality, type of modulation and
other technical characteristics. And a nice, appropriate box cannot be
bought, it is up to you to make it. It can be something as on pic.3.11 or
similar. The idea can be also found in some catalogue of radio receivers’
manufacturers, or you can think of something of your own. As far as the
author of these lines is concerned, he likes best the wooden boxes from the
20’s and 30’s of the previous century, from the times of the charleston, E.
H. Armstrong and Al Capone. They looked something like those on the pic.5.17
and can serve you as an inspiration for your personal design.
The mid button is for the variable
capacitor for station tuning, the right one is for the potentiometer for
volume regulation. The button on the left can be a rotary switch for turning
on/off (S). It can also be a tone regulation button, and for the
reaction-type receivers it can be a button of the potentiometer that
regulates the magnitude of the reaction. In the last two cases, the on/off
switch (S) is located on the regulation potentiometer. The outside antenna
and ground hubs are located at the rear panel of the box. The wires
connecting the hubs with the PCB should be isolated, flexible and long
enough to be able to open the panel and put it at upright position.
If the receiver is power supplied from the outside net, a green LED should
also be added, as the power indicator. The good place for it is just above
the variable capacitor’s button, instead of the triangle-shaped marker.
Pic.5.18 shows the parts for the first box from pic.5.17. For the front and
rear side two pieces of 5 cm thick plywood, measuring 22 cm x 15 cm are
needed; for the side panels, two pieces of 10 cm thick plywood, 15 cm x 9
cm, and for the bottom side - one piece of 10 cm thick plywood, measuring 13
cm x 9 cm. The best way to cut these parts is to be done by the carpenter on
the special machine, since only then will they be of strictly rectangular
shape, and bottom and side panels will have exactly the same width, which is
very important during assembling. On the front side, the circle and the arc
are drawn with the aid of the sector, and the cutting is done with the
carving saw. The part that is cut from the back panel will serve as a
closure. When it is cut it isn’t necessary to treat it with emery, since it
will fit nicely in the hole on the rear panel even if it isn’t cut evenly.
On the inner side of the rear panel two plywood lattices measuring about 2
cm x 13 cm should be nailed. Four wood screws will be screwed in them later
(the holes are shown as four dots), which will serve to tighten the closure.
Connecting of the pieces is done with the wood glue and small nails. Before
you start hammering, it is very useful to drill a few holes for the nails in
the front and rear panel with 1 mm drill. The nails are partially hammered
into the panels, the edges are then covered with glue, and the nailing can
then be done. When all this is finished, the box should look as the drawing
at the right end art of the pic.5.18 *vertical stripes over the loudspeaker
opening are not shown. They can be omitted, and you can nail in a few thin
lattices, when the box is finished, as shown on the last drawing on the
pic.5.17). The semicircle part is made of 5 mm x 5 mm lattices, or similar,
which are put side by side on the upper edges of the front and rear panels,
that are covered with glue (the picture shows only one of these lattices).
When the last one is fitted, the space between them is filled with “putty”
that is made by mixing the fine wooden chips with the wood glue, with the
aid of a steel plate. After that, the lattices are tightened to the panels’
edges by two pieces of strong scotch tape, which are shown in dashed lines,
and everything is left to dry well. When drying is, after about 10 hours,
finished, all the edges and lattice parts that protrude are well flattened
with emery. All the remaining holes are filled with the fast-drying putty,
and everything is abraded once again, and the putty is applied again, and
abraded again, etc., until the upper part is semicircle-shaped, all the
sides smooth and the edges correct.

* Before the loudspeaker is attached with
screws, a piece of decorating cloth should be placed between the panel and
the loudspeaker, which will protect it and contribute to better looking box.
* Perhaps some of the readers will seem that there’s a lot of exaggeration
in previous lines, and even too much pedantry. There’s a Latin proverb, that
says: AGE QUOD AGIS - Do the things you do, which, in our case, can be
interpreted as: You should either make the box properly or not making it at
all.
* This box is relatively small, it is predicted for the loudspeaker that is
about 12 cm wide. If you have bigger loudspeaker, and it will certainly play
both louder and better, you should make a bigger box. The dimensions
calculation is done by dividing the diameter of the bigger opening, that
will suit bigger loudspeaker, in centimetres, by 11, and all the measures on
pic.5.18 are multiplied with the number attained. E.g. if the diameter for
the new, bigger hole is 15 cm, new dimensions are obtained by multiplying
the old ones by 1.36.

5.7. Bimboard, Protoboard . . .
The readers that have carefully studied all
the radio receiver projects that are described here, have possibly noted
that the author referred to experimenting either with values of some
components or with entire circuits, and all that was in order to practically
find the optimal solution. When small changes are discussed, such as finding
the optimum value for some resistor, that can be done on the previously made
PCB. In case of bigger changes that of course is not convenient, and
sometimes it is almost impossible. For all kind of electrical diagrams
check-outs as well as various experimenting with all electronic devices,
including radios, it is the best to use a special experimental board, which
can be purchased under various trade names: protoboard, bimboard, matador,
steckplatine, steckboard etc. All of them have in common that component
connecting is done without soldering, by simply inserting the legs into the
small holes on the plate.
As an example, pic.5.19 shows a full-scale experimental board that can be
purchased in one of the Belgrade electronic shops. It has 630 vertically
aligned holes, connected internally in 126 groups of 5 holes each, and
another 100 holes placed in two topmost lines, connected in two horizontal
groups by 50 holes each. The connections between the holes are inside the
board and cannot be seen, they are shown on picture in dashed lines. The two
topmost parts are used fo bring the supply voltage, and the battery or the
adaptor is connected to them. One of them, most often the one that has minus
pole connected to it (in all the devices described herein), also serves as
the device Ground. The holes contain miniature metal hubs that are elastic,
so when a leg is popped in, a reliable mechanical and electrical junction is
accomplished. The distance between the adjacent holes is 2.54 mm (1/10
inch), which allows for connecting the vast majority of electronic
components, which are being produced with inter-leg distance that is equal
to a hole number multiplied with 2.54 mm (in the producers and sellers’
catalogues the 2.54 mm distance is marked as R, which stands for raster, and
the components that have their legs horizontally and vertically distanced to
2.54 mm multiplied by some whole number are said to have their legs in
raster).
The necessary electrical junctions between the hole groups are accomplished
with connecting wires that can be bought at Conrad, but are more often
self-made from plastic-isolated 0.5 mm or 0.6 mm copper wire. These pieces
vary in their length and can be bent as the biggest piece in the lower left
part of the pic.3.19, although it is better and nicer to use regular pieces,
shaped as the cyrillic letter P.
Pic.5.19 also shows an example of practical usage of one such board. The
radio-receiver from pic.3.15 is made on it. As can be seen, the coil ends
are stuck into the holes whose coordinates are j,37; j,39; i,45; i,47, the
diode in holes i,39 and i,45, the pin No.1 of the IC in e,54, etc. With the
connecting wires the legs No.1 and 3 are connected, the ones that are
connected with the potentiometer slider, and legs No.2 and 4 are connected
to the ground by means of 4 connecting wires (the minus pole of the
battery), etc.
It is now clear that experimenting is done in a very simple manner. E.g. if
you are interested how does a capacitance of C2 affect the tone colour in
the headphones, all you should do is remove it and insert a capacitor of
greater or smaller capacitance, etc.

* The hubs on the board are elastic, so
that conductors of various diameters can be easily inserted. No wires much
thicker than 0.6 mm should be inserted, since the hubs will deform. The
components whose legs are too thick as the variable capacitors,
potentiometers, transformers and similar, are connected over pieces of wire
that are soldered to them.
* It is useful for the connecting wires to be made with isolations of
various colours, so that red ones could be used e.g. for connecting with the
+ battery pole, the black ones with Gnd, the yellow ones for the signal etc.

5.8. Universal PCB
Practical realization of simple radio
receivers, as well as other simple electronic devices, can be done in many
ways, as it was discussed in PE No.2. One of those is shown also in this
number. That is construction of the detector receiver from pic.3.11, where
some of the components are mounted onto the box walls (the variable
capacitor, coil and the hubs), while other (the diode and two
block-capacitors) are placed between them. With some skills, and by the aid
of few smaller nails nailed from the inside of the front panel, a more
complex device could be made, say, that from pic.3.12. But this solution
would start looking as “the dead cockroach technique”, which will be
discussed in the “Funniest Electronics”. The real solution is the PCB that
can be made from the drawings that are given, or those you will draw
yourself, together with the instructions given in chapter 5.1.
There’s another option for practical realization. It is a universal PCB,
that can be bought in the electronic components’ stores. There are more
sorts of these PCB’s, and all of them have in common that the holes on them
are drilled on the distance of 1/10 inch (R=2.54 mm).
One of the universal PCB’s is shown on pic.5.27. It consists from a huge
number of round copper isles, with hole in the middle. The components are
being soldered first (resistors, diodes, IC’s, capacitors...), and then the
component pins are connected by pieces of isolated copper wire, on the
soldering side.
As an example, pic.5.28 contains the photograph of the receiver from
pic.3.21-a that is made with the universal PCB from pic.5.27. It can be
placed into a box as on pic.3.21-c, except the box should be bigger, in
order for the loudspeaker to.


5.9. A Modern Oldtimer
The receiver on pic.5.22 is designed for
the readers that wish to make a semi-conductor model of a complete direct
radio receiver that was being produced many years ago, with electronic
tubes. It had a total of 3 tubes, one of the contained the HF pentode
(utilized in the HF amplifier) and the diode (used in detector), the other
one had a triode (pre-amplifier) and powerful pentode (power amplifier),
whilst the third one contained the duo-diode (the rectifier).

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