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    • #8275
      LectronFan
      Moderator

      Hi all,

      The more I experiment with Lectron, the more I spot differences between the different transistors and their use.

      They each have their advantages

      Let’s look at the Legacy Germanium transistors.

      Their advantage is the lower Base Emitter voltage (about 0,3V), ideal for quick switching circuits. They also have a build in resistor (680K, 330K and 100K), which saves mounting space.
      But this is also a disadvantage ! Due to the resistors, some circuits simply wont work or need  adaptation.

      Also, Germanium transistors tend to drift. This means that their amplification factor Hfe is dependant of the ambient temperature. The same transistors differ also. You can try this by building circuit 51a and 51b in the legacy manual and watch the differences in meter reading, even if they have the same resistor value build in !

      So, as for the Silicon transistors there’s much more stability.

      Since they don’t have the resistor build in, its much easier to adapt their Hfe to the circuit. They don’t drift by temperature which makes the circuit perform better. They need more space on the board though.

      Since they don’t leak current (Germanium transistors do), they can be better used for DC coupled stages.

      In our Lectron environment, the Ubungs System 1102 and OpAmp labor are 2 examples of a fine marriage between Germanium and Silicon transistors.

      And this is what I tend to strive for too ! Many future constructions will show off the advantages of both types.

      What are your opinions ?

      Many greetings

       

    • #8278
      Guenni75
      Moderator

      Hi all,

      I have been working with Germanium transistor since about 1960 – as one of my several hobbies. The history with their different techniques was very diverse since 1948: point contact / grown junction / alloy junction / diffusion alloy / drift / surface barrier / mesa / etc., even npn symmetric*.

      Every production process had a special goal, so every “type class” had advantages – except temperature, as Frank mentioned.  I love the “old” outlines, no plastic, no uniform look. So I am collecting even the very first pocket radios since 1954 with the TO-22 outline from Texas Instruments, Hitachi and Sony. Furthermore the glass versions like OC44 … OC75 or OC602 … OC614. And these transistors are still working very good since that time without problems.

      Germanium npn transistors in glass case were the OC139…OC141, described as symmetric* and could be replaced in some applications by two diodes (…?). Philips designed some pocket radios with the OC140 and OC74 as complementary push-pull output stage with OC75 as driver and a subminiature hearing aid transistor OC59 as pre-amplifier. Looking into such radios I must always laugh… that’s the diversity I like – heaven knows why. The look into radios since 1970 is most boring to me.

      This very special amplifier is since many years the last active Lectron block in my superhets with pnp types:

       

      The 1-transistor-reflex-superhet I introduced a while ago was another good example for the very special usage of (selected) germanium AM BC pnp transistors – only some Japanese types (drift types ?) worked without changing the bias resistor (or other parts of the circuit). European types only very few with some changes, Russian types were very “special”: extreme amplification / sensivity, oscillation etc.

      The germanium transistors in the Lectron blocks (AF: AC173, AC151 and RF: AF126) with the built-in bias resistor may be bypassed by using the (universal) transistor blocks with a socket. Then npn or pnp, Ge or Si, RF or AF, low power or medium power types may be used depending of the actual problem / circuit.

      In this photo from ~ 1970 Max Guerth used in this experiment a couple of this socket blocks:

       

      Silicon types are always first choice, but in circuits / models / applications before ~ 1970 I like to go “old”  – with all pro’s and con’s.

      Best,

      G.

      • This reply was modified 6 months ago by Guenni75.
      • This reply was modified 6 months ago by Guenni75.
    • #8652
      bodger
      Participant

      Speaking of germanium transistors, I found an old OCP-71 germanium phototransistor and took a close-up picture of it, thought you might be interested.

      Cheers,

      John

    • #8663
      Guenni75
      Moderator

      What a wonderful and detailed photo of the OCP71 – thank you! It’s a Philips OC71 without black painting.  It shows the internal construction of  the years 1955 … 1960 in Europe.

      The http://WWW.Radiomuseum.Org would like to show this photo on their OCP71 page (I am the semiconductor admin…) so I ask you for a approval – we can display your name as the owner.

      Best regards,

      Guenther

    • #8666
      bodger
      Participant

      Yes, you may have my permission to use that photograph on radiomuseum.  I tried to get a membership there a couple of times over the years, but was unable to figure out the process.

    • #8668
      Guenni75
      Moderator

      Membership of RMorg:

      I had to try how to find the right way… and here is it: on the main page go to the left column to line HELP and click Contact Forum. The new page shows under 1. to get the membership – then follow the “clicks” / language choice and Sign In (and a one time payment / donation of a few dollars for all the hard- and software costs of the foundation – and thousands of members and dozens of admins for their worldwide work).

      Enjoy – and best regards,

      Guenther

    • #8809
      bbarry
      Participant

      I was reading this forum about the differences in the transistors.  This evening I was reviewing experiment 42 on page 17 and found that the experiment was incorrect.  In step 2 of the experiment, the bulb goes on and not in step 2.

      I am including a pic that I took for your review of the Supplementary Instruction manual’s experiment #42.

      • This reply was modified 1 month, 3 weeks ago by mwpeters75.
      • This reply was modified 1 month, 3 weeks ago by mwpeters75.
      • This reply was modified 1 month, 3 weeks ago by mwpeters75.
      • #8813
        mwpeters75
        Keymaster

        Hi,

        Do you mean that the bulb will not illuminate in step 1 (typo possibly which says step 2)?

        Thank you for spotting this!  I am afraid that this is not the only such error in the Supplementary Manual 🙄

    • #8814
      LectronFan
      Moderator

      Hi Bbarry,

      I’m afraid the manual is correct !
      In setup 1, the lamp must light when pressing the switch.

      In setup 2 it should not.

      When I look at your picture, the lamp should not light !
      Current can not flow agains the arrow in the transistor block.

      I’m very afraid that your transistor is broken.
      Can you check with another one ?

      Greetings

       

    • #8815
      bbarry
      Participant

      Michael, I have tried every single transistor.  Even the transistors that were recently forwarded to me do not work.  Is it possible to open the transistor blocks carefully and replace them with silicon types?  Also, is it possible to purchase new blocks that will work with my current set?

      • #8817
        mwpeters75
        Keymaster

        Yes, the post Egger block white tops (which were glued) can be carefully opened as they use mini posts to attach to the clear block.  You can then replace the failed transistor.  Sorry that the sent blocks are not working correctly 😥

        Yes, the legacy transistors were still available until recently.  It seems that Lectron, GmbH has stopped doing any sort of business.  I am not sure yet whether or not this will be a permanent situation.  Mr. Pohl’s son Martin informed me a couple of weeks ago that he no longer works at Lectron, GmbH and that staff was significantly cut back in March.  I wish that I had better news.

        • This reply was modified 1 month, 3 weeks ago by mwpeters75.
        • This reply was modified 1 month, 3 weeks ago by mwpeters75.
    • #8816
      LectronFan
      Moderator

      Hi Bbarry,

      This just comes to me : is it possible that you used a different light bulb ?

      It should be a 6V and 50mA light bulb. Other types may destruct your transistors.

      The Base-Emitter junction is quite delicate and can not handle more then a certain milli ampères .

      I will make more tests and measurements this evening and will let you know.

      Greetings,

      Frank

      • #8820
        mwpeters75
        Keymaster

        Thanks so much Frank for all your help!

    • #8821
      LectronFan
      Moderator

      You’re welcome Michael, I’m glad I can help !

      Hi Bbarry,

      So I constructed the 2 circuits and everything works as described in the manual.
      Could it be possible that your light bulb is not the correct one ?

      There’s always a possibility to open the boxes and replace the transistors. Use a sharp cutter to cut between the top and case.

      I hope this is not needed.
      Can you build an oscillator circuit to check the transistors ?

      Have you read my forum posts ?

      I always explain that we need a protective resistor in series with the lamp. This is a basic rule for experimenting and will save the delicate transistors.

      Here the 2 circuits with protective resistors.

      The BE junction is always delicate so please be attentive when experimenting.

      Keep us informed !

      Circuit 1Circuit 2

      • This reply was modified 1 month, 3 weeks ago by LectronFan.
    • #8851
      bbarry
      Participant

      Frank, I did purchase a newer bulb and did try your recommendation.  Unfortunately it did not work.  I would like to replace my transistors with Germanium varieties so I would need to replace the 100, 330 and 680 ohm transistor modules.  The 680 Ohm RF has 4 leads but it is hard to find and I don’t know who is a good supplier.  Can you provide me with some sources?

      Thanks again for your time and I am sorry it took me so long to reply.  Please stay safe!

       

    • #8853
      Guenni75
      Moderator

      …there’s an actual offer on the wellknown internet auction platform from Canada: AF121

      NEVER use the 680kΩ biased RF transistor for other things than RF – the original AF126 (and the AF121 above) are only for 1 mA (Ibe) or 10 mA (Ice).

      AF126

      • This reply was modified 1 month, 1 week ago by Guenni75.
    • #8855
      LectronFan
      Moderator

      Hi Bbarry,

      I was looking for a good supplier the last days and I’m afraid that the best chances to obtain these is via EBay, just like Guenther mentioned.

      Theres still a chance however, I know a firm here in Belgium who may still have these Original transistors on stock.

      I will make a call tomorrow and ask about the price.

      I will post then here the price with shipping to you.

      If some one else is also interested, let me know.

      Please consider that the AC125 transistors have a Max. collector current of 100mA.

      The AF125 transistors have only a 10mA current and may never be used to drive replays, lamps, speakers.

      Most circuits of the original Lectron manual lack safety resistors. Be sure to Always use a resistor of min. 47Ohm in series with the light bulb.

      Depending of the model of relay used, this may also need a resistor.

      If you want to be on the safe side when you are constructing a circuit, use a 47Ohm or 120Ohm resistor connected in series with the battery.
      With a 47Ohm resistor, the max. Current flowing will be then 200mA.

      With a 120Ohm resistor, this will be then  75mA.

      An advantage of using a battery over a power supply module is that a 9V battery is limited in delivering current.

      Please check the experiments published in this forum for more details about these protection methods.

      Always double check the circuit for errors.

      Your transistors (and other components) will benefit from these protection measures.

       

    • #8857
      LectronFan
      Moderator

      Hi all,

      Good news ! I’ve contacted a supplier of electronic components today and he still has some of the AC125 and AF124 (is the same as the AF125) transistors in stock.

      The AC125 costs 3.2 euro each and the AF125 costs 4.3 euro each.

      Since these are small and lightweight components, the shipping to USA costs 5.5 euro when the package weighs lesser than 100 grams.

      So if someone is interested let me know.

      Kind regards,

      Frank

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