Another such neat trick is in most simple photographic flashes: the neon bulb which indicates that flash is ready also provides feedback to the flyback charging supply by increasing it's load when correct voltage is reached.
And then there is typical CRT degaus circuit, which produces the required damped oscillation waveform by running mains voltage throught two thermally coupled thermistors.
Edit: Horizontal deflection circuits of CRT TVs and monitors are usually full of neat tricks: shifted hysteresis inductors, deriving various voltages from the flyback and output multiplier, synchronisation of main SMPS switching frequency to horizontal retrace... One can view CRT VGA monitor as one big switchmode power supply with video amplifier bolted onto it (and many CRT monitors are actually mechanically built this way, with RGB video going directly from the captive VGA cable to amplifier on the neck board)
Some people have decided to fix this by using an electronic voltage circuit to get a clean 5V from the noisy 12V supply. But the instruments just wouldn't work right.
It seems the instruments relied on the 5V supply being jittery. With a smooth voltage, the mechanical instruments would get stuck.
Watch a pilot in an older airplane. He'll tap the gauges, too, to get an accurate reading.
It's very elegant, but if you take out one, it goes haywire.
Are you sure that this is not a https://en.wikipedia.org/wiki/Vibrator_(electronic) that would be powered by a solenoid and not just a bimetallic strip?
You were actually initially right, I searched for that actual part and it is indeed a bimetallic strip along with a heater (that turns off when the strip moves away from a contact) and not a device with a solenoid/relay.
Apparently whatever it supplies is tolerant of that sort of interruptions in its power source -- I imagine that it would operate on a quite lower frequency than a "vibrator"-type power supply where magnetic force moves the contacts (and elasticity returns them).
The thing is, the instruments require the noisy 5V.
You can buy kits with an electronic 5V source, and also to replace the old guts of the instruments with modern ones. That retains the original look, with modern accuracy and performance.
Probably all multisync monitors I've seen have actual neon lamps and I believe that these neon lamps are in fact crucial for the "multisyncness", because they provide time for the control electronics (which given the package and pinout seems to usually be 8051) to settle after mode change without blowing out the CRT.
For a long time I've considered all the warnings of the "wrong video mode may damage your display" kind as nonsense. Then about ten years ago I had blown two 12" POS monochrome CRT monitors by unintentionally running them at 1024x768@75Hz, there was correct image for about a second followed by loud bang.
If regular CRT televisions behave the same way, that means at some point in time it would have been possible to create a "jamming signal" that transmitted a signal with the wrong refresh rate and blew up all the TVs in the area.
There is nothing stopping non-multisync monitors (including TVs) from trying to sync to an out of range signal and depending on the design they might damage themselves trying.
It's kinda the same as the move from internal combustion engines to electric. The discrete parts count drops to a tiny fraction of the former. (Though, I guess if we were to count transistors in an IC as individual parts, LCD trumps CRT.)
Then again, one could build a CRT without a billion dollar fabrication facility. The same can't be said of LCDs (AFAIK).
Regardless, I really enjoy these posts. I don't understand half of it (though I understood more of this one than usual, as my dad owned a TV shop when I was a kid and I got some hands-on experience with CRTs early in life), but they're very satisfying. I wish I could play with cranky old computers more often.
The pinnacle of analogue electronics and precision is the line of Tektronix analogue oscilloscopes. They are marvelous from just about every angle. Each box is a blend of physics, mathematics, mechanical and electrical engineering that is simply unsurpassed. The engineering is reminiscent of the space race. No expense spared. Everything covered in gold and full of precision machined parts.
My current favorite Tektronix unit (I have a few!), a 475, is 42 years old, works perfectly and is still classified as relatively high performance compared to modern equipment. And the knowledge gained from looking after it and understanding it is STILL valid and STILL 100% usable in 2017.
Someday, I'll have more time to play with electronics. It's something I enjoy, and I have most of the tools for it (except a scope), but I always seem to have too many other things requiring my time and attention.
I worked with high-end 90s-era Tektronix scopes when I worked in television. They definitely weren't pure analog by that time, as they had memory and a variety of modes providing both digital and analog data, but they were still pretty cool.
But it feels like it’s lacking a soul.
Playing around with Electronics is my disconnect from reality for a bit. Works pretty well :)
If You find any of your father’s stuff, spend some time with it. It helps things believe it or not.
I guess those days are over?
They’re still perfectly useful instruments to be honest.
The volume control knob abruptly stopped working; the organ was stuck at maximum volume.
He opens it up to discover the volume control simply controls the brightness of a light bulb, which had burned out.
The light bulb shone on a photo resistor, which governed the output volume.
Coming from the reinforcement side, a lot of DJ gear baffles me. They look at audio much differently, which I suppose is understandable when you’re mixing two decks with an occasional bandpass versus a 50+ channel metal band with subgroups and racks of outboard effects.
So, how do faders and knobs work nowadays?
Oh, are they perhaps still potentiometers, with the difference that you can now low-pass filter them before reading off and digitising their values, since you don't have to pass the audio signal through them?
1. One of my DMM's, a Fluke 8600A, has a light bulb in it as part of the charge circuit: https://i.imgur.com/TMvRmKF.jpg
2. My Tektronix DM44 strapped to the top of one of my scopes has one as part of the ohmmeter input circuit.
3. Also used for amplitude stabilisation in feedback networks in the negative feedback path.
Very common tricks and very useful little things.
Only problem is they get hot, eat a lot of current and snuff it occasionally. They were replaced by JFETs for typical feedback applications.
Some photos: https://photos.app.goo.gl/cn1CV9ts5sINLlwa2
You can see the 10181 ALU chips - these are ECL versions of the popular 74181 ALU.
That's because the bulb doesn't have 600V across it. In a normal application as an actual glowing bulb, it's rated to have 28V across it, pass a certain current, and emit light at a certain brightness.
In this application, it's being used as a current limiter, and the high voltage supply to CRT grids is very low current (several milliamps at most) --- thus, the current through the bulb and the voltage across it will also be very low.
It's not uncommon to exceed forward constant max current specs for an LED with pulses (PWM), for example.
Light bulbs are sometimes used for stabilizing oscillators. I think it works like an (audio) volume "compressor" would.
For example the Thorens TD125 turntable uses a light bulb as part of the oscillator circuit that generates the AC signal that powers the motor.
Not everyone has this gift of being able to explain stuff in layman's terms even if they are expert on the subject. Carl Sagan was best at it, on the other extreme you have those that use jargon beyond the audience's knowledge, pretending to know but not understanding it really. This whole Alto series has had some great writing in it.
That warning light also has a second, and even more important, function. It induces a load on the alternator to energize the charging coils. A few hours spent removing what I thought was a defective alternator and $100 having it rebuilt. Only to find out it was a $1 bulb.
In this digital world analog circuits are like witchcraft to me. How you think things work is not at all how it works.
Alternators have a circuit such that when the battery current is no longer needed (the alternator has spun up and is putting out more voltage than the battery) an arrangement of diodes cuts off the battery field coil circuit and then the light goes out.
When the alternator is self-energizing, there is a feedback mechanism then at play which controls the field current, keeping the alternator voltage level: without it, the voltage would rise uncontrollably: more voltage from alternator -> more current through field coil -> greater induction of voltage. Before the alternator is self-energizing, what regulates the field current is that bulb.
So that is to say, if you see the light on all the time when the alternator is spinning, that warns you that it's not actually working. It is not it's not putting out enough voltage (perhaps none at all) to overpower the battery circuit and become self-energizing. This could be because the rotor coils are burned out, or other problem: wiring or whatever.
Since that bulb is off most of the time, we don't expect to have to change it very often.
If an alternator bulb has burned out, and the unit is not very old, that could indicate a problem.
Going back and forth with alternator mechanic he asked me to pull the instrument panel and inspect the bulb.
The globe was powered from a mercury cell, and because it's voltage was so constant, the light stayed at constant brightness.
Then a simple plastic lens overlayed alternate stripes from the image and the globe. The user adjusted the aperture until the stripes vanished, which guaranteed that the exposure was correct.