[fun] Weird electronic circuits collection

RF sweep generators used "wobulator" vibrating capacitors.

Mechanical choppers/vibrators were the basis of early microvolt-level amps and meters.

And of course car radios used vibrators as both dc-ac converters and sometimes synchronous rectifiers.

There were lots of rotating things too: motor-generators, field-excited generators, amplidynes, HF generators as radio transmitters.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

OK - you win. The thing is still more British than the old Ellie, as British as furlongs / fortnight.

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-TV

Alexanderson alternator transmitters, for instance.

Dual-gate MOSFETs make pretty good low-leakage track/holds.

One of my faves was using the accurately-known threshold-crossing rate (TCR) statistics of shot noise to generate a detector threshold. By servoing the TCR at a lower threshold to be exactly 5 kHz (5.5 sigma in the given bandwidth), a higher threshold could be set at 7.1 sigma to ensure a false-count rate of about one per day (1E-5 Hz), even with a true count rate much higher than that.

(note the shiny new web site) ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Also used in analog computers to get four-digit resolution/accuracy.

Some serious fraction of a Hz, I'd expect.

The only time I actually did it was to charge oil caps from a neon sign transformer, battery and rheostat at the end of a long insulating shaft, with the servo loop being me turning a knob.

That was my flashtube/PMT lidar, when I was a kid.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Nice. Shiny. But why isn't Highland Technology a link?

We should add a link to your site on ours, in the electro-optics section. We have a marketing meeting this week and I'll see if The Brat is willing.

I should make my own web site and build a fan base. But I'm too lazy to do the web work.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

You could chop a small voltage, amplify it, and drive one phase of a

2-phase AC motor. It would then spin and do something to balance a bridge. Analog XY recorders did that, with linear slide pots to close the loop, millivolt ranges. Somebody (Digitek?) made a neat DVM that worked that way, with a 10-turn pot and a veeder-root digital readout.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

In addition to the chopamps, the analog computers I worked on in college had servo multipliers and sine converters that worked quite like that.

Because Dashing Firmware Hunchback forgot. I'll get him to fix it.

Sure thing. Collaborating with you folks is fun.

Well, if you generate the content, you can use Wordpress or something like that. DFH did a full-custom one, partly for educational purposes.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

It was an American machine :-)

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~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk

"Settled down" is right. I remember making point contact transistors from germanium on the kitchen bench at home, the next step up from cats whisker rectifiers using lead sulphide ( galena crystals ) for crystal sets.

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Regards, 

Adrian Jansen

A rapidly vibrating metal point inside a glass tube dipping in and out of a pool of mercury and switching a small current. The make-and-break action at mains frequency generated a comb of harmonics going right up into the SHF spectrum.

It was made by Marconi Instruments and I saw one in the research and development department of Eddystone Radio n the late 1960s. It was being used as a wideband noise source for calibrating and measuring the noise figure of the first commercial UHF receivers.

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~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk

A negative tramway booster.

It was used to overcome the volt drop in the rails which formed the return circuit for the tramway [streetcar] traction current. There was a very strict limit on the allowable potential between the rails and true ground because of the fear of electrolytic corrosion in adjacent metalwork. With a heavy load current, the rails at the far end of a long circuit could easily exceed this voltage.

A cable from the power station was laid alongside the tracks and bonded to the rails at some suitably distant point (usually about 1/3 of the distance from the far end). In the power station was a generator, mechanically driven by an electric motor from the main traction supply. It fed power into the cable at around -10 volts and could carry several hundred amps of returning traction current. It was a very strange looking machine because the frame and armature were quite small but the commutator and brushgear were massive.

Now here's the clever bit... The field windings were in series with the main power cable for that section of track, so it generated a negative voltage which varied in sympathy with the traction current and always exactly cancelled the voltage drop on the rails at some point carefully chosen for optimum overall correction. There was a shunt across the field winding which could be adjusted to maintain the correct cancellation and it was made of a similar material to the rails, so that their temperature coefficients tracked together.

Another of these machines could be placed in series with the power cables running to some remote feed-in point. In this case, it generated a boost voltage which exactly compensated for the volt drop in the feeder. In effect it behaved as a virtual negative resistance which cancelled out the real resistance of the cable.

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~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk

Rods / Blue Moon?

Direct heated valves ought to do better than that.

NT

Tell us more about these "helical log-periodic aerials". That's a new one to me. I know helical, and log-periodic, but both? Is it some kind of conical spiral?

Clifford Heath.

That was it. They were wrapped in some sort of dark-coloured weatherproofing material (fibreglass?) and looked quite menacing.

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~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk

Sorry for resorting to the Daily Wail, but they do have some of the best (and most searchable) photos.

Seeburg

--
~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk