Unusual functions of cheap parts

Did you know that a carbon arc acts as a negative resistance? Run the arc on DC and put an LC tuned circuit in series with the arc (coil of heavy copper tubing) and you have a powerful oscillator.

We worked with a company that was developing an xray imager, and was buying very expensive electrically conductive glass (gigohms per square sort of range.) They discovered that certain welding glass was identical and about 1/20 the price.

John

Certainly.

I used arc welding glasses when conducing these experiments.

Some trivia:

In the silent film era, actors had eye problems due to the UV radiation from arc studio lamps.

Most of the usable illumination from the arc lights is actually from the glowing carbon electrodes.

"Automatic arc lights" used a solenoid in series with the arc to keep the distance constant between the poles regardless of carbon electrode burnout. I assume that if this is to be used with a AC arc light, both the moving coil as well as the static coil should carry the arc current.

Paul OH3LWR

A 2N2369 is a gold-doped NPN, gold-doped to kill storage time and improve recovery from saturation. I don't recall any PNP device with gold-doping... or the equivalent.

...Jim Thompson

And optocouplers can do interesting things:

Very simple high-voltage opamp, up to 400 volts p-p.

Isolated totem-pole driver, from a few volts up to 400.

Current limiter.

Low-leakage diode, sort of like an LED painted black.

John

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Exactly-when I was a kid we made them like this all the time. As I recall, it came from "700 scientific experiments, with illustrations"...

John Devereux wrote in news: snipped-for-privacy@cordelia.devereux.me.uk:

To save power, use the LEDs of a backlight to measure the ambient light to decide to switch the backlight on or not.

M.

The Motorola McMOS handbook (2nd edition 1974) warns about this usage by pointing out that by cascading three such AC coupled stages, the last stage will be saturated by the noise from the first stage.

Paul OH3LWR

I posted some opamp schematics to abse a while back. I guess I could do it again if they're no longer available.

The others chould be fairly obvious.

John

Switching a 20 year old 24v weller soldering iron on and off is a good test for seeing if an 8051 cpu board is EMC proof

martin

Right, if CTR > 1.

John

Going the other direction, I used the elements from a toaster as a load to discharge wet-cell lead-acid batteries. It was a discharge/charge cycling test.

John

But, it's a bit easier to degauss your picture tube with a soldering gun than with a refrigerator.

John

E.G the CMOS 4007. See the old handbooks for a '100dB amplifier' based on a RCA chip - there was a wiring error in that old description - IIRC it was 3800? - whatever, the 4007 is the same chip.

Murray vk4aok

A latch.

btw, do you know a standard complementary pnp-transistor for the 2N2369, such like 2N3905 but with higher ft and less feedback capacitance? It seems that the manufactorers have almost no data on their internet pages.

mfg. Winfried

It ran off 120 V. Parse the sentence as "two D-cell-carbon arc lamp." An earlier poster talked about building AC-powered arc lamps using the carbon rods from dry cells.

Cheers,

Phil Hobbs

It also works for this: Vcc !/c --/\\/\\/\\---+------! ! !\\e V ! --- ----/\\/\\/--+--- too load ! ! --------------------

You get a current limit and an indicator light.

As a youngster I played with TTL DIP-ICs in my chamber and my parents next room felt that the tv was going crazy. The pins had long wires...

- Henry

schrieb im Newsbeitrag news: snipped-for-privacy@g43g2000cwa.googlegroups.com...