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    • #8773

        Hi all,

        Summer is arriving, unfortunately travelling is not permitted till now.

        Lets have some fun with a circuit combining legacy and modern modules.

        I’ve build a mystery circuit. Who can tell (or guess) what happens when using the upper and/or lower switches ?
        Can you also see how the power connections have been made ?

        The battery is wired to the circuit in a rather strange way, who can tell how this comes ?

        As a change, I’ve used a picture of the setup.

        Write down your comments here !
        Wish you lots of fun with this experiment.

        Mystery circuit

      • #8775

          I had to build this circuit – before I got no idea… Pressing the lower button will turn the light on, the upper button causes the light to go off. So it works similar as a Flipflop.

          The battery: I can not see any strange connection so far – give me a hint!


        • #8776

            <p style=”text-align: justify;”>Hello Guenther,</p>
            Electronic circuits are sometimes mysterious, not ?

            Glad you took the time to build this experiment.
            Actually, this circuit is a thyristor.

            By closing the lower switch, we put a small voltage on the “gate” and activate the thyristor.

            By closing the upper switch, we are “opening” the feedback loop so the thyristor deactivates.

            A hint for the battery connection anomaly : check the grounding of the circuit 😉
            I will publish soon a version with 2 silicon transistors, the diagram will be clearer.


            Another question, Why is there a capacitor of 0,1uF in the circuit ?

            Will it still work without ?




          • #8777

              Hi all,

              As promised, here a thyristor circuit made with a NPN and a PNP Silicon transistor.

              It is in fact an equivalent circuit. Lectron has also a thyristor module nr. 2418.

              A thyristor has 3 connections, a Gate, a Cathode and an Anode.

              In our circuit, the lamp is connected to the “Anode”.

              The upper switch is connected via a voltage divider (made of the 4,7k and 1,5k resistors) to the “Gate”.

              The lower switch is connected to the “Cathode” .

              A thyristor is like a switch with remote control.

              When the Gate is grounded, the path between the Anode and the Cathode is open. This means that the light bulb doesn’t lit.

              Once we connect the Gate to a positive voltage, the path between Anode and  Cathode closes and the light bulb is lit.

              When we remove the voltage at the Gate, the path between the Anode and Cathode remains closed.

              Only by disconnecting this path (by pushing on the normally closed lower switch) the thyristor resets at its beginning position.

              The circuit seems somewhat compacter than the one with the Germanium transistor.

              Here is “an open air” circuit of the thyristor.

              A question, why is there a 1,5k resistor in the circuit ?

              After building this circuit, you’ll find out !



            • #8778

                Coming back to circuit #1: after removing the 0.1µF capacitor nothing (new) happended – it works in the same way as before.

                And why not using (-) as GND – since 1953 the so-called GND changed with nearly every radio model / maker / whatever circuit. Always since that time PNP and NPN transistors (first Germanium, since ~ 1963 more and more Silicon types) were used in a mix (instead or as a compliment, for example push-push stages without transformers). Car radios had an external switch for changing (+) or (-) to car chassis GND.

                So I used in a second experiment this variant – and needed 9 blocks less = > 24% (!)

                The 0.1µF capacitor was not needed for the asked function, neither with the PNP Germanium (above right) and nor with the PNP Silicon transistor (inserted block).

                With the second circuit (easier to understand like electronic dummies like me 😉 I will report soon.



                • #8783

                    Professors Frank and Günther,

                    Thank you both for the challenges presented in the Lectron System circuits that you have presented.

                    My newest acquisition (thanks again Günther and Frank) of the Ausbausystem 5 includes a thyristor block.  Unfortunately, no instruction manual came with the unit.  The Ausbausystem 5 had some similar subject matter to what would become the KfZ model focusing on automotive electronic systems.  Experiment 11.68 in the KfZ manual discusses the role of the thyristor (part #8100 423) in power control applications.

                    Here is also a link to provide an overview of what the thyristor component does (yes I had to educate myself on this subject although I was familiar with the component with its GE branded name of SCR).

                    • This reply was modified 3 years, 3 months ago by Michael.
                    • This reply was modified 3 years, 3 months ago by Michael.
                    • This reply was modified 3 years, 3 months ago by Michael.
                • #8792

                    The designation SCR – for Silicon Controlled Rectifier – was chosen 1957 by GE and is still common in USA. Westinghouse used the designation Trinistor, and Europe combined Thyratron and Transistor to Thyristor.

                    The 4 layer construction is PNPN – where the first P is the Anode, the second P the Gate und the last N the Cathode.

                    There are also Thyristor Tetrodes / SCR Tetrodes available; here has the first N layer also a connection = Gate. So this type can be switched by 2 Gates – one with negative and the other with positive voltage.

                    Photo thyristors and other special versions are available, too, even in integrated circuits.

                  • #8794

                      Now I have finished the 2nd experiment with silicon transistors – but after “power on” the bulb is ON, so I always have to STOP with the lower switch. Then all is working good, until the next power OFF / ON…

                      Removing the resistor 1.5kΩ will cause malfunction, because the NPN transistor base is “hanging in the air” and cannot work as designed.

                      The circuit only works rather well with Silicon transistors; I tried to use a PNP Germanium transistor (like in experiment #1) but this time without success. The block covers are equal, but everybody has to have a look inside: TO-1 outline = Germanium, TO-92 (or TO-106 in this photo) = Silicon.

                      By the way: the transparent “Steck” blocks (plug-in) had the article numbers #8199002 / 8199003 (PNP), the “normal” versions #814405…8 (PNP/NPN).

                      The battery block #8100540 (9V, neutral contacts – later #2124) was available since 1975 and came with the “Physik Experimentell” training set from Mr. Saucke (who wrote the Buchlabor and developed the “Spulenbaustein” #810505 (#2706) etc. The thyristor #8100423 (#2418) is – together with many other semiconductors – from the 197x years, so these all are “legacy” versions, too… May be a co-working of Mr. Guerth / Mr. Birett and Mr. Timmer around 1970.



                    • #8795

                        Hi Guenther,

                        Glad you are involved in examinating the circuit’s improvements !

                        When looking in the 1205 box, I discovered a PNP Germanium transistor without resistor !

                        To distinguish between Ge and Si transistors, the new Germanium transistor Modules have a Ge marking.
                        It was included with the OpAmp experiment set. I thought I hadn’t one.

                        I will try your circuit out today and wil report.

                        Concerning the 0,1µF capacitor, it was needed in my setup or the the thyristor got triggered when powering on.

                        It works as follows :

                        When power is applied, the capacitor starts charging. Since there’s a current flowing through it when charging, it momentarily shorts the Base of the NPN transistor to Ground.

                        This is a kind of POR (Power On Reset) and prevents false triggering of the Thyristor.

                        Glad to see that you seems not needing it. Have you tried several times reconnecting the power without having the problem that the lamp starts to light up immediatly ?


                        • This reply was modified 3 years, 3 months ago by LectronFan.
                      • #8798

                          Hello Michael,

                          Hmm, I’ve seen this set before on Ebay ? 😉

                          This seems a combination set of the new Motor set and KFZ set.

                          The new Motor set uses driver blocks for controlling the motor, thus really using the motor in working circuits.

                          It seems that the Ausbausystem 5 has only a TRIAC and empty transistor modules.

                          Perhaps it was the idea to use “loose” power transistors for driving the motor.

                          The modern MOSFET modules 2443 and 2444 are able to drive the high motor currents (as seen on some experiments posted here in the forum).

                          Can you provide more details about this set ?

                          Which components are used and which “loose” transistors came with this set ?


                          • #8802

                              Hi Frank,

                              Please examine the photo I provided of the Ausbausystem 5.  You will see a Diac (8100 425), a Thyristor (8100 423), Zener Diode (8100 422), and a ‘Leistungsdiode’ (8100 421) in addition to the Triac (8100 424) that you mentioned.

                              This is a very rare model despite its longevity in the price lists.  I can’t tell you too much about it because no instruction manual came with this particular unit.  I therefore cannot say what are authoritatively the correct blocks that should be in the ‘official’ Ausbausystem 5 model.  There is no known cut sheet or brochure for this model either.

                          • #8799

                              Sorry guys,

                              Another post for today !

                              Guenther’s new design of the first circuit made me experiment 😉

                              As PNP transistor, I used the Ge version 2429 without resistor (included in the OpAmp set).

                              Instead of the lamp, I would love the use the led with resistor 2407 (also included in the OpAmp set).

                              But, the circuit stopped from working !

                              So time to think about this and make it work again !Thanks to the easy and versatile Lectron system, this was quickly done.

                              To make it exciting, I would like to get the Lectroneers at work and find also the solution.

                              A hint : only 2 passive modules have to be changed. A passive module can be a resistor, capacitor, coil, wire.

                              An active component can be a transistor, diode, integrated circuit.

                              Please post your solution here !

                              Oh yes, now the circuit performs well with the led or with the lamp.

                              Good luck !

                            • #8800

                                Hello Frank,

                                first of all: the usage of a LED can be realized with a parallel resistor of 120Ω … 2.2kΩ.

                                The problem with my version of your experiment #2 is solved with a 0.1µF capacitor:

                                And the 0.1µF capacitor in experiment #1 was worthful; the first 2…4 times the circuit worked o.k., but then the problem occured… so your version is well.

                                Best regards,


                                • This reply was modified 3 years, 3 months ago by Guenther.
                              • #8804

                                  Hello Guenther,

                                  I think it depends of the gains of the transistors whether the capacitor is needed or not.

                                  But to be on the safe side, it deserves a place in the circuit 😛

                                  Aha, your solution to the led problem is a good find, but not the ideal solution !

                                  Indeed, when shunting the output with a resistor will make it work. But the current draw will increase.

                                  Lets assume that we would like to save our battery thus using a led. So, the first design (using your better setup) should be modified by changing 2 components.

                                  The question remains, which ones ?


                                • #8807

                                    Hi everyone !

                                    Here’s the solution for the led usage : just replacing a resistor into 100k and swapping the 0,1uF capacitor for a 10k resistor makes it work.

                                    Since we use the led instead of the lamp, the voltage across this component will  be higher since the led draws lesser current.

                                    Thus we need to adjust the voltage divider to the base of the NPN transistor.

                                    Using a 100k and a 10k resistor does the trick !


                                    Led thyristor

                                  • #8808

                                      Hi Frank,

                                      I just looked at your solution – and I have to say that I would never have come to this solution quickly…

                                      I will build it myself in a few days and compare the electricity consumption, among other things.
                                      Thank you & best regards,


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