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Two quick questions

  1. Jun 22, 2011 #1
    So, I come to you today with 2 more of my amazing 11 year old questions about physics.

    I'll make it short here:

    1. I have an awesome Eco-friendly power source idea that I'm not gonna post here 'cause it's too original. First of all, my basic knowledge of what electricity IS, is electrons jumping from one atom to another (I know, stupid sounding right?) but how do you initially get electrons to start moving? Plus, in silicon, is it the silicon atoms that let electrons jump from one atom to another, or is it just that electrons pass through the silicon atoms or something else?

    2. I have a radio from like 1939 (My great grandfather) and as a summer project, me and my dad are gonna try to fix it. It's really old and has a few vacuum tubes. First off, is there a place to get new vacuum tubes? Is there a place to get big bulky old-timey transformers and capacitors too? Thanks for the help,

    Lazernugget

    (Oh and by the way, YES I HAVE A SOLDERING IRON)
     
  2. jcsd
  3. Jun 22, 2011 #2

    dlgoff

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    Electrons "drift" through conductors. i.e. their velocity is very small compared to the random movement they are going through. I'll leave it up to you to follow through on these links.

    micohm.gif

    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html" [Broken]

    Not only do electrons move through silicon but also holes.

    intrin.gif

    http://hyperphysics.phy-astr.gsu.edu/hbase/solids/intrin.html" [Broken]

    2. I have a radio from like 1939 (My great grandfather) and as a summer project, me and my dad are gonna try to fix it. It's really old and has a few vacuum tubes. ...[/QUOTE]

    This reminds me of my early projects. I have a box of old tubes that I may share with you. Let me know the tube number when you get to that stage and I'll check. You can PM me if you want.
     
    Last edited by a moderator: May 5, 2017
  4. Jun 23, 2011 #3
    For the old radio part...

    Google should be your friend. There are lots of tubing enthusiasts out there still and folks who have hoards of back stock. But I've found that most often it's the capacitors that go bad or dry out or short or whatever. Usually they are marked with a farad and voltage value so you can make an attempt to find replacements, or even build-up what you need with multiple new smaller caps. The main problem these days will be finding the voltage rating, so remember that you can put 2 identical caps in series to double the voltage rating but it halves the capacitance.
     
  5. Jun 23, 2011 #4

    dlgoff

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    Mentioning voltage brings up something that should be noted for safety. Care should be taken not to touch anything in these old radios while they are plugged into the power source. These tube circuits require some fairly hefty dc voltages. e.g. the maximum plate voltage for the 6CA7 pentode is 800volts and when used as a class A amplifier is 265volts.

    http://en.wikipedia.org/wiki/EL34" [Broken]

    Also note that some tubes have metal caps that connect to the plate.

    http://en.wikipedia.org/wiki/Vacuum_tube" [Broken]

    edit: one other thing comes to mind concerning safety. Back then, power receptacles were "two pronged" and did not have the third terminal for chassis safety ground. So when you plugged them in, you had a 50:50 chance (depending on the orientation on the prongs) of placing 115vac directly on the chassis.
     
    Last edited by a moderator: May 5, 2017
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