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Thread: Vintage ammeter - photos

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  2. The Following 3 Users Say Thank You to Altair For This Useful Post:

    baja (09-25-2020), nova_robotics (09-24-2020), rgsparber (09-24-2020)

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    Supporting Member rgsparber's Avatar
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    I once developed a negative 100.208K resistor. I used one of these fine meters that read 20 micro amps to test it with zero noise. Great instruments!

    Rick
    Rick

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    Supporting Member DIYSwede's Avatar
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    Quote Originally Posted by rgsparber View Post
    I once developed a negative 100.208K resistor.
    Sorry, Rick - but I just can't get heads or tails outta that sentence, but isn't that firstly a 100.208 MΩ resistor?
    And then being "negative" also - "a resistor with a negative resistance" - hence simply a DC-to-light linear amp?

    Reminds me of my DIY audio design years where I and some of my co-dependants kidded:
    "just design an audio interconnect cable with a negative resistance, infinite input impedance and zero ohm source impedance,
    no inductive or capacitive reactance, and we'll get rid of all those heavy, ugly amps entirely"...

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    Supporting Member rgsparber's Avatar
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    Quote Originally Posted by DIYSwede View Post
    Sorry, Rick - but I just can't get heads or tails outta that sentence, but isn't that firstly a 100.208 MΩ resistor?
    And then being "negative" also - "a resistor with a negative resistance" - hence simply a DC-to-light linear amp?

    Reminds me of my DIY audio design years where I and some of my co-dependants kidded:
    "just design an audio interconnect cable with a negative resistance, infinite input impedance and zero ohm source impedance,
    no inductive or capacitive reactance, and we'll get rid of all those heavy, ugly amps entirely"...
    It was a -100.208K resistor. Put it in parallel with a +100.208K resistor and you get an open circuit:

    Rtotal = (R1 x R2)/(R1 + R2) = (100.208K x [-100.208K])/(100.208K + [-100.208K) = (-10000K/0) = infinite which is an open circuit.

    The resistor was accurate to +/- 20 parts per million per year and took up an 8 x 11 circuit board. The cost was around $10K back in the 1980's. It more than paid for itself. Oh, and it could survive an indirect lightning strike yet operate from +200V to -200V.

    Yes, negative resistor are real and useful. In grad school I made negative capacitors, inductors, and even negative diodes for my Master's project. How does that bend your mind?

    For those EE's out there, I once built an audio circuit with a driving point impedance that formed a circle as you went from 200 Hz to 3200 Hz. It used 3 transistors and was used in an analog phone connection to join three phone lines.

    Rick
    Rick

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    Supporting Member DIYSwede's Avatar
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    Quote Originally Posted by rgsparber View Post
    Yes, negative resistor are real and useful. In grad school I made negative capacitors, inductors, and even negative diodes for my Master's project. How does that bend your mind?
    -Thanks Rick. It doesn't bend my mind at all - that sentence just doesn't have any "explanatory value" to me
    -it merely introduces a brand new and very subjective use of the word "resistor".

    IMHO: In common usage of the word, a "Resistor" (but also "Capacitor", Diode" & "Inductor") denotes a passive component.
    All passive components consume power (they're hence called "Passive") - but a "negative resistor" would produce power.

    In my personal beliefs and daily use of the terms, a passive component cannot show static negative values
    w/o violating "the law of conservation of energy" and/ or 2nd law of thermodynamics.

    I can totally buy that you've designed and built active circuits showing negative resistance, capacitance and inductance.
    That's a meaningful sentence having some explanatory value, at least to me...

    Just my two cents - but perhaps you used to work for "Reversed Entropy Inc. -
    where we simply and directly turn heat into current"
    ?

    Pardon me for my Megaohm mistake above, got confused by the decimal point...

    Cheers
    Johan


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