[fun] Weird electronic circuits collection

VDF as valve in various apps. It does depend what you mean by legitimate.

NT

Resetting an op amp integrator by inverting the power supplies. (Turns the ESD diodes into a bridge.)

Dimly illuminated LEDs as subpicoamp switches with controllable bias current (as used in Footprints).

Inverted BJT switches.

Pease's voltage inverter (zener the BE junction and C goes below E)

Williams-tube (CRT) memory

Cheers

Phil Hobbs

A common sensor for liquid nitrogen levels, is a carbon resistor. Resistance of carbon (a semimetal) goes up sharply when it gets cold.

Wiegand wire; a magnetic core that toggles between two permanent-magnet polarities, is a B field sensor element that generates accurate repeatable pulses.

Microwave oven: an odd use for oscillator vacuum tubes.

Den torsdag den 7. december 2017 kl. 18.52.03 UTC+1 skrev Piotr Wyderski:

universal remote using the transmit LED as light sensor for recording ir

Reverse biased GaAs LED as Spad. (single photon avalanche detector.)

Very inefficient, but fun.

It started on SEB when someone questioned the V_rev. max of all leds as 5V.

George H.

Cheap rectifier diodes used as kilovolt:nanosecond pulse generators.

PHEMTs used as diodes

PHEMTs used as switches (they are generally characterized as linear RF things)

Transistors used as reference zeners

LVDS receivers used as comparators

PV optocouplers used as floating power supplies, sort of what you mentioned.

Mosfets used as heaters

Surface-mount resistors ditto

PCB traces ditto

CRTs used as signal processors

PMTs as noise generators (like radar jammers)

Vacuum tubes as vacuum gages

Capacitors used as power amps

Capacitors used as varicaps

Varicaps used as opamp front ends

Capacitors used as temperature sensors

Neon bulbs used as xray detectors

Mosfets ditto

DRAMS used as imagers

EPROMS as xray detectors

FR4 used as a thermometer

Water used as a resistor

Korg MS-20 voltage-controlled filter, using reverse-biased BJTs as the variable resistance element:

Soviet Polivoks voltage-controlled filter, adjust cutoff frequency by current-controlling op-amp GBW:

Use a bridge rectifier as a variable resistance:

Page 11 of this app note where an entire McIntosh 75 tube power amplifier is used as a schematic component for an isolated high voltage op-amp power booster:

High voltage regulator using an LM317 and pass tube with the LM317 connected between the tube's cathode and grid:

Build an audio power amp out of voltage regulators:

You can make a LDO out of a TL431 and a couple other parts. You can make a MFB filter out of a TL431. You can use two TL431 to make a high-gain differential amplifier. You can make just about anything out of a TL431

Making smoke :-)

I built a 1kW+ RF amp from five color TV horizontal flyback tubes because they were formally rated at 30W plate dissipation. That way we got around the 150W plate dissipation limit. Many ham radio operators in Germany did that.

Years later they closed this loophole and legislated 750W max RF output. Not sure if older amps are grandfathered but knowing Germany they probably aren't.

This is the amp:

Below is the "post-loophole" amp I built, throttled to 750W but it could send that into an almost dead short if needed:

Contact wear (as in relay points) maximized and named 'electrical discharge machining'.

Mercury-in-vinegar with an iron nail, the 'Beating Heart' oscillator.

Battery powered, Oxford bell ... which is uneconomic (no repeat battery sales)

Wasn't there some European country that in the early days of radio taxed receivers on the number of tubes they had, so some clever company had a custom tube built that contained all the plates, grids, and cathodes required to make a suphert, inside a single envelope? LOL

Never heard of that one but I could imagine their tax guys pulling such a stunt. I still have grandpa's radio which has such a tube. It can be called the first integrated circuit because there are also resistors and caps in it:

Some European countries used to set property taxes according to the number of windows so frugal people bricked up a few windows to save on taxes.

If you dig through the old radio-design literature you'll find all sorts of interesting designs.

There are some in which the incoming signal flows through the same tube elements twice: e.g. it's both an RF amplifier and an audio amplifier. There's a separate detector stage with a high-pass on its input and a low-pass on its output.

There are other radios (quite a few) which share significant parts of the circuitry between the AM and FM RF/IF paths. In some cases, a triode or pentode which serves one role for AM reception, serves a completely different role for FM reception.

And, yeah, tubes with two different sets and types of elements (e.g. a pentode on one side and a triode on the other) were quite common.

I don't recall ever hearing of one which rolled up "magic eye" tuning-indicator functionality with a more functional active section such as a pentode, but it wouldn't surprise me much if at least one such existed.

Using the current limit and thermal limit of (many) 7805 regulators as a temperature controlled heater for diesel injection pumps running on straight vegetable oil:

Same in many of the closet lighting systems, the LEDs are used as door opening sensors for a moment.

Best regards, Piotr

BTDT.

I have never used it in practice (so far), learnt about it from you.

BJTs ditto. CA3046 used as a heater, sensor and active ovenized element of something temperature-sensitive.

Common way to heat the mirrors in buses.

As storage elements -- yes, but processsing?

How? Electrostatic amplifiers based on saturable dielectrics? (another item to be added to the list).

Another idea I learnt from you, could be very potent.

What for?

Best regards, Piotr

Why?

As strange a circuit as you wish, but without irreversible violation of its SOAR. BC107 used for switching kiloamperes wouldn't count. ;-)

Best regards, Piotr

And in the UK, many remain bricked up 1.5 centuries after the tax disappeared. (The tax itself also lasted 1.5 centuries)

Powering and clocking an MCU at the same time by connecting a coil to its XTAL_IN pin and some other pin and using the ESD diodes as an RF bridge rectifier.

Best regards, Piotr