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.