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# Thread: Vintage ammeter - photos

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)

3. 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

4. Originally Posted by rgsparber
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"...

5. Originally Posted by DIYSwede
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

6. Originally Posted by rgsparber
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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