• This topic has 10 replies, 3 voices, and was last updated 2 months ago by rj4u.
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    • #8534
      rj4u
      Participant

      Hi all, thought you might be interested in my copy of the Raytheon  Lectron 820 set that I have built. I posted some information on this set about 4 weeks ago and since then the set is near completion. A few minor issues that I will discuss in a future post. For this post I have provided a picture of what I have assembled. I plan to post details of all the blocks and perhaps go through all the experiments in the Series 3 manual. Most work correctly. There are a few concerns and I will be asking the power users some questions over the parameters of some of the blocks. For what it’s worth,

      Thanks,

      Bob

      • This topic was modified 2 months ago by mwpeters75.
      • This topic was modified 2 months ago by mwpeters75.
    • #8536
      mwpeters75
      Keymaster

      Hi Bob,

      Thanks so much for your latest and most fascinating update regarding your model 820 built from scratch.  Truly a unique creation!  I look forward to your future updates with more details and concerns as you go through the experiments.

      Best regards,
      Michael

    • #8540
      LectronFan
      Moderator

      Hi Bob,

      Now,  you’re ready for mass production !

      Just kidding, this set is an eye catcher, well done !

      I recommend using strong neodymium magnets underneath each cube to make a sturdy construction.

      For the ground connection, you can use these magnets for contacts. Some of them have small eyelets where you can attach a wire using a bolt and nut.

      Did you use a special earphone ?

      I would love to see a circuit build with this set.

      Greetings

       

    • #8542
      rj4u
      Participant

      LectronFan,

      Thank you for your comments.

      All connections are made with neodymium magnets both underneath for ground and also for connection between cubes. I will provide more details later this evening.

      Earphone is still an issue. Obtaining a 300 ohm earphone is not impossible, just a pain. More on this also.

      Back with more details in a bit.

      Bob

       

    • #8546
      rj4u
      Participant

      Transistors:

      100k and 300k with AC125. Here I used an ‘equivelent’ NTE102A.

      680k RF resistor AF126. Used ‘equivelent’ NTE160

      In process of parameterizing these transistors. The AC125 and AF160 can be found and I may ebay some to see how close they are to the NTE’s. NTE’s were easier for me to get.

      My tuner block seems to have a measured resonance in the AM band but I have not had much luck with the three transistor AM radio. Amplifier sections seem as though they are working. I need to spend more time first calculating what the circuit gains should be and then measuring on the bench. Could simply be that I have poor reception and this amplified crystal radio is hard pressed to bring anything in without a mile of antenna.

      That’s about it for the actual build. I am an avid wood worker so machining the parts was pretty straight forward. Still, why anybody would do this I don’t know. Actually I do, because I can share this with others and perhaps spark an interest in engineering and building.

      I will start with circuit demonstrations tomorrow.

      Regards,

      Bob

       

    • #8547
      rj4u
      Participant

      So it’s pictures that need moderation……

    • #8545
      rj4u
      Participant

      Battery Block:

      9 volt batteries are the worst batteries ever. This 9 volt power block is a 3.4 volt lithium polymer 1.5 AH. This is feed through a USB 5V battery management circuit that allows it to be charged from a USB port. See small slot at end of block. Two holes on top show charge status LEDs. 3.4 volts connects to boost converter for 9 volt output. Not bad for most circuits. Slight bit of switcher ripple on output that probably impacts AM radio circuits. Maybe not, but I intend to do surgery on this block and add some additional output filtering.

       

       

    • #8544
      rj4u
      Participant

      Special and problem blocks:

      Speaker Block:

       

      The speaker block has a 300:8 ohm audio transformer. Actually a 600 ohm center tap to 8 ohm using the center tap for 300 ohms. 2.5 inch 8 ohm speaker.

      Question: What is the DC resistance of the 300 ohm side of a real Lectron speaker block?

       

      Earphone Block:

      My problem with the earphone block is in actually obtaining a 300 ohm earphone. To overcome this problem with circuits that use the earphone as a 300 ohm resistor, I have simply created a 300 ohm block.

      Next post: Power block

    • #8543
      rj4u
      Participant

      The blocks,

      This photo shows the typical components of the component block. Two neodymium magnets for each of the two or three connect faces. North/South polarity on each face. Single magnet on bottom for (+) ground plane. Ring lug associated with each magnet for electrical contact between bricks. Component and lid.

       

       

      This photo shows component soldered to ring terminals which are part of the magnet assembly. Repeat for all components. Ring lug added to bottom magnet in cases of need for ground connection.

    • #8551
      LectronFan
      Moderator

      Hi Bob,

      Thank you for the very detailed pictures, it all becomes clear how the contacts and magnets interact.

      Concerning your 9V battery block. This is a great idea to use a polymer battery and booster converter. Indeed, as you mentioned, the booster can cause interference in audio circuits like amplifiers and radios. A suitable coil in series with the output and capacitor across the output terminals might reduce this. Experimenting is the key to success!

      Concerning the speaker block, I measure a DC resistance of 28 Ohms.

      So, care must be taken if we design a circuit using this speaker. Check the experiments published here on the forum how this could be done.

      Wish you all the best and a good health

    • #8552
      rj4u
      Participant

      Thanks for the DC measurement. 28 ohms falls right in line with what I measure.

       

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