The "All American Five", & more dangers!!

[Mp3]

It's a tradeoff. You guys get to power a jackhammer off the outlet in your kitchen because of 220/240v, we get to be more careless with mains due to the lower voltage.

In regards to the earthing aspect.....
Japan does this as well and is actually worse because the earth in Japan is the screw on your outlet. Likewise, an American came up with the lightning rod method of grounding So does it come as much surprise that our design philosophy is to do as much work with as few parts as possible?

I mean, does it really matter on 100-120v mains? My whole life i've plugged things in either way around and they work. If the plug isn't polarized so it can only be put in one way. And even then, the majority of American households made before the later-mid 1900's out here have awful nightmarish electrical wiring.

Half the outlets in my apartment built in the late 1800s - ancient as far as USA buildings go - are wired backwards. The worst that happens is a spark when you plug something in. (I know, some of you in other countries probably can't fathom that, but it's one of the joys of low mains voltage)

Anyway, if you look at trends in American design philosophies, we have an affinity for having a minimal amount of components do a large amount of work. A lot of designs that came out of the USA that compete with European/Australian/Asian designed boards are way more overbuilt, way more simplistic, and expected to be treated MUCH worse IMO. (We are really rough with our belongings compared to other nations, I think)

[vk6zgo]

(Please don't move this. It's mainly about 'general' topics)..
The "All American Five" refers to the mass produced valve radios, by very many manufacturers, from the 1930's. Apart from the standard 5 tubes & their functionality, their emphasis was on 'cheapness' of manufacture. There is/was NO power transformer, and relied on the American line voltage of 110/120-v to directly feed Plates (partly via resistors), and series connected tube 'heaters' of higher Filament Voltages etc., so that no mains transformer is/was needed.  OK, I get it, but half the time, one ended up with a 'Live' Chassis for the uninitiated!? 

So many times, I've seen ccts where a 'power' switch, if any, actually switches the Neutral!  The VAST majority of power plugs I've seen in America have only 2 pins, and no 'Earth' pin. Now I know that most 'modern' plugs/sockets there now are 'polarized' by way of a slightly wider pin, but still with no Earth??  I understand too that this is 'just' 110v, not 240v like in Australia, but I don't understand the attitude. I see numerous Youtube videos where people in the U.S. plug equipment into un-switched outlets on their bench. Ok, YOU might have wired it correctly. 

In Australia, we MUST have an Earth too, unless the device/machine is 'Double-Insulated', like a certain hair dryer etc. It just seems that America is more blase' about Neutrals & Earthing ?? (And yes, I understand about isolation transformers & isolated Variacs etc.) 

(Please don't move this. It's mainly about 'general' topics)..
The "All American Five" refers to the mass produced valve radios, by very many manufacturers, from the 1930's. Apart from the standard 5 tubes & their functionality, their emphasis was on 'cheapness' of manufacture. There is/was NO power transformer, and relied on the American line voltage of 110/120-v to directly feed Plates (partly via resistors), and series connected tube 'heaters' of higher Filament Voltages etc., so that no mains transformer is/was needed.  OK, I get it, but half the time, one ended up with a 'Live' Chassis for the uninitiated!? 

So many times, I've seen ccts where a 'power' switch, if any, actually switches the Neutral!  The VAST majority of power plugs I've seen in America have only 2 pins, and no 'Earth' pin. Now I know that most 'modern' plugs/sockets there now are 'polarized' by way of a slightly wider pin, but still with no Earth??  I understand too that this is 'just' 110v, not 240v like in Australia, but I don't understand the attitude. I see numerous Youtube videos where people in the U.S. plug equipment into un-switched outlets on their bench. Ok, YOU might have wired it correctly. 

In Australia, we MUST have an Earth too, unless the device/machine is 'Double-Insulated', like a certain hair dryer etc. It just seems that America is more blase' about Neutrals & Earthing ?? (And yes, I understand about isolation transformers & isolated Variacs etc.) 

The AA5s were more a thing of the 1940s on.
If you look at most published 1930s US radio designs, they used power transformers, with secondaries of from 285 to 385 volts "a side".

Factory made Radios were fairly expensive  back then, & a lot of circuits were designed for a fair bit of output power for use with the fairly inefficient "Electrodynamic".speakers in common use.

After WW2, the USA manufacturers wanted to produce cheap radios.

For some reason, power transformers were expensive, & "series string" tubes fairly inexpensive.
This, along with the fairly low (then) 110v Mains supply, lent itself  to the "AA5" design.
Other developments, like more efficient "Permag" speakers, & improvements in tube efficiency also contributed.

In Australia, the economics went another way:-
Tube factories had massively increased their production during the War, but virtually all the tubes they produced were in the heater voltage values  of 1.5v, 2.0v, 3.0v, 6.3v (the vast majority) & 12v.
There were also, in the early days, many hundreds of surplus tubes on the market, mostly 6.3 volt heater types

Higher voltage heaters suitable for "series strings" were not normally made, & usually had to come from the USA, the UK, or Europe.
The higher Mains voltage in Australia also made the case for transformerless designs much less compelling .
Transformers for domestic radios were neither excessively large or heavy, nor, in the Australian context, expensive.

The upshot was what became fairly standard in this country----- a 5 "valve" "mantel" radio  using a power transformer, a tube rectifier, a mixer, one stage of IF gain, then a detector/audio driver stage (a "double diode, hi mu triode") & an audio power tube(usually a beam tetrode of the 6V6/ 6AQ5/6M5 ilk.

There were a few "transfomerless" radios around----some custom made. for the few remaining DC Mains Supplies.
Of these, some were 110v DC, & the relatively simple "AA5"type circuit could be used.
Others were 240v DC, & the radios were messy things with series resistors, "barrettors", etc.

Transformerlesss designs were dubbed "death radios" & loathed by radio servicemen.

[nfmax]

Transformerless TV sets - known and marketed as AC/DC designs - were very common in the UK. More valves makes series heater strings feasible with 240V mains. Surely the AC/DC TV set must have been a thing in Australia, of all places? 

[vk6zgo]

Transformerless TV sets - known and marketed as AC/DC designs - were very common in the UK. More valves makes series heater strings feasible with 240V mains. Surely the AC/DC TV set must have been a thing in Australia, of all places? 

Nope!
When TV arrived in Oz, the valve type TVs followed the same pattern as the radios, using a transformer, with a 300-350v "a side" at 300mA secondary.
The early ones used things like 5V4s for the rectifier.
They soon moved to silicon diodes, for a while retaing the centre tapped HT winding, then later, 200-odd  volts non tapped windings with a voltage doubler.

By 1956/57, DC  Mains supplies were reasonably rare in Australia,  so the advantages of being compatible with AC & DC were not very compelling.

The only AC-DC TV I remember being sold here was an early Admiral "portable" .
It was hardly that, as it needed to be plugged into the Mains.
It didn't sell all that well, & was discontinued after a few years.

A lot of people worry about the weight of power transformers, but. you can hold a "mantel set" transformer in the palm of your hand, & carry it around,
Similarly, you can pick up & hold a BW TV power transformer in the same way although your  hand would get a bit tired after a while.

After having become used to carrying Australian BW TVs, I picked one up in England, expecting it to be lighter, but, too my surprise, it felt about the same.
I think much iof the weight of such a TV is the tube, chassis material, & the extra safety stuff which is not needed on the transformer equipped  version, leaving the relative weights pretty much the dame.

When colour TV came to our shores, we went straight to standard SMPS in the locally made TVs.
The imported (mainly Japanese) TVs did the same.
Both sides of thei Mains were isolated from the chassis, with the only connection to it being on the secondary of the high frequency transformer in the switchmode.

We never had the SMPS built around the Horizontal output circuit that was evidently common in UK & EU.
.

[16bitanalogue]

<snip>

[Yes Nader's book did help kickstart some important changes, but calling the Corvair "unsafe at any speed" is pure hyperbole. Sensationalism to sell books.

I'll quickly summarize your position:

"It is owner's responsibility to understand our cheap, flawed, mass market design."

Be honest, did you even watch the video you posted?

[TimFox]

... Consolidated Edison in New York finally ceased DC distribution totally in 2007. ...

To be fair to Con Ed, I think they carried on with DC service for such a long time because there were a few elevators in NYC that used DC motors.  Substituting AC motors and controls was apparently deemed to be a bigger problem than just continuing DC service to the few ancient DC installations.
A search brought this article:
https://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/

Apparently the hold outs haven't converted to AC. They just installed AC to DC converters on site.

Yes, the very late dropping of DC service in New York was related to elevators.  However, before the War, there was a lot of DC distribution in New York and Boston, a big problem for transformer-operated equipment and the origin of AC-DC jokes (another topic). 
Around 1965, I visited the roundhouse of the Duluth, Missabe, and Iron Range Railroad in Proctor, MN, which still had one or two Yellowstone 2-8-8-4 simple articulated steam locomotives (the most powerful ever built, slightly more tractive effort than the more famous Big Boys of the Union Pacific).  The big electric motors ran on 25 Hz power for historical reasons, which they could still obtain from Minnesota Power and Light Co., although the rest of us enjoyed modern 60 Hz power.

[andy2000]

Transformerless TV sets - known and marketed as AC/DC designs - were very common in the UK. More valves makes series heater strings feasible with 240V mains. Surely the AC/DC TV set must have been a thing in Australia, of all places? 

Transformerless TVs were common in the US well into the 90's.  They did have a polarized plug in the later years, but the chassis was hot regardless of which way the plug was inserted (the negative side of a full wave rectifier was tied to the chassis).  They used an isolation capacitor on the antenna inputs, and made sure there were no exposed metal parts.  Higher end sets with A/V inputs often used optoisolators, or transformers to isolate the inputs.  Occasionally, they installed an isolation transformer, or even added a SMPS to higher end models rather than redesigning the whole set.   

It wasn't an issue other than having to remember to use an isolation transformer while servicing them. 

[james_s]

I'll quickly summarize your position:

"It is owner's responsibility to understand our cheap, flawed, mass market design."

Be honest, did you even watch the video you posted?

Absolutely it is, and yes of course I did. I've been a car enthusiast all my life, I've not yet had an opportunity to drive a Corvair but I'd love to do that. I've driven lots of other interesting and unusual cars, vintage stuff is a lot cooler than anything you can buy today, it's a whole different experience.

Everything is flawed, it's called compromise, can optimize for a number of factors, you can't have it all. You must be very young, cars are a lot different today than they were even 20-30 years ago. Also you seem to have fixated on the Corvair, what about the SUVs that are prone to rolling due to the high center of gravity? Is it not the owner's responsibility to understand this "flawed" design and not drive a big tall truck the same way they'd drive a low slung sports car?

My point is not that the Corvair was a particularly good car, but it was nowhere near as bad as the hype you have bought into. Like the enormously popular VW Beetle it was engineered to be cheap and fuel efficient, and with that came some compromises. I'm going to assume you've never driven a Corvair, or even Beetle or any other cars of that era, you're simply parroting what you've heard without any experience to back it up.

[Sal Ammoniac]

So many times, I've seen ccts where a 'power' switch, if any, actually switches the Neutral!  The VAST majority of power plugs I've seen in America have only 2 pins, and no 'Earth' pin. Now I know that most 'modern' plugs/sockets there now are 'polarized' by way of a slightly wider pin, but still with no Earth??  I understand too that this is 'just' 110v, not 240v like in Australia, but I don't understand the attitude.

We have 330 million people here in 'Murica, so we have a lot more spares than you do in Australia in case someone gets fried. 

[16bitanalogue]

I'll quickly summarize your position:

"It is owner's responsibility to understand our cheap, flawed, mass market design."

Be honest, did you even watch the video you posted?

Absolutely it is, and yes of course I did.

...and that the manufacture also has responsibility to make sure their product is safe. Which leads one to...

Everything is flawed, it's called compromise

This. Duh.

what about the SUVs that are prone to rolling due to the high center of gravity? Is it not the owner's responsibility to understand this "flawed" design and not drive a big tall truck the same way they'd drive a low slung sports car?

There is as fundamental difference between "flaws" which appear when the vehicle is pushed to its limit and real flaws that arise from everyday driving. ESC and other electronic nannies, side skirt air bags, crumple zones certainly have made SUVs safer. That's is the fundamental point that automobile safety was an issue even before Nader's book, although hyperbole for some, highlighted the indifference of car manufactures toward safety during that time.

My point is not that the Corvair was a particularly good car

Exactly.

but it was nowhere near as bad as the hype you have bought into

Nope. Per the conclusion in the video that you posted, it was not as bad as it was made out to be, but it did have its problems that lead to loss of control - directly from head GM engineer at the time.

Like the enormously popular VW Beetle it was engineered to be cheap and fuel efficient, and with that came some compromises. I'm going to assume you've never driven a Corvair, or even Beetle or any other cars of that era, you're simply parroting what you've heard without any experience to back it up.

Different cars with the same suspension, yet not the same problem. Per the video that you posted, from the head GM engineer stated the excess weight (due to the rear engine) also played a role.

I never argued that the Corvair was a horrendous death trap. In fact, I stated that it certainly has its flaws (you finally admit to that), the video you posted concluded with that, and that Nader's book (among other articles and studies) highlighted automobile safety concerns. The Corvair was an (exaggerated) example used, but certainly flawed as, again, admitted by you and the video you posted, to propel the industry toward safety.

Please do not continue to dig into this hill you are hell bent on dying on, because now I am just arguing with a stone wall.

Cheers.

[rsjsouza]

I told this story somewhere else in this forum, but I grew up with non-polarized and non-grounded round and flat plugs all my life in Brasil. The standard until the mid 2000s was to try to be friends with the US and some of Europe's standards and we got away with the ground plug in most types.



With the explosion of the PC era in the 1990s, the three prong grounded US plug started to become quite common and, with the existing non-grounded and non-polarized outlets, the obvious solution was to rip apart the third pin - not without that tingling sensation when one touched the metal housing. Worse, a lot of people started warning about cutting the third pin and therefore a market of "electricians" was created, retrofitting the existing outlets by simply replacing the outlet but not wiring the ground. Most houses and buildings were only two-wire circuits unitl 1994, where the new constructions required the ground wire but everything else was grandfathered.

Fast forward to mid 2000s, the stupid swiss standard was approved, which was pretty much incompatible with everything else in existence in the country and in the world and from night to day it obsoleted hundreds of millions of appliances, equipment and parts. Someone made wads of cash then.

The newer standard is safer? You bet. The older standard was useable? Of course! Did people get shocked? Yes, but it was considered a growing pain, really. Given that electric appliances and gadgets were not as ubiquitous as today, people gave it the proper respect it requires and used it in a much more responsible way.

I see the case with the safe/unsafe cars the same: in my experience, the individuals had much more respect for the act of driving due to the mechanical limitations of a car and knew they could really die if pushed above certain limits - the safe car propaganda tends to infuse a sense of indestructibility, where people become so confident they even consider (and several actually do) deviate their eyes from the traffic to interact with their smartphones. And no, I am not saying that we should roll back the incredible progress done with the safety aspects, but we should equally stress the dire consequences even with all this techno-nanny gizmos.

As others have said, you can't make the world "safe at all costs". A part of the responsability has to come from the individual.

[Electro Detective]

@ rsjsouza: great comment 

but someone has to say it..that's an awesome collection of wrist bands in that picture 

Iron Man would be green with envy 

[rsjsouza]

@ rsjsouza: great comment 

but someone has to say it..that's an awesome collection of wrist bands in that picture 

Iron Man would be green with envy 

   
I have never saw them from this angle... you are right.

[GlennSprigg]

... Consolidated Edison in New York finally ceased DC distribution totally in 2007. ...

To be fair to Con Ed, I think they carried on with DC service for such a long time because there were a few elevators in NYC that used DC motors.  Substituting AC motors and controls was apparently deemed to be a bigger problem than just continuing DC service to the few ancient DC installations.
A search brought this article:
https://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/

Apparently the hold outs haven't converted to AC. They just installed AC to DC converters on site.

Yes, the very late dropping of DC service in New York was related to elevators.  However, before the War, there was a lot of DC distribution in New York and Boston, a big problem for transformer-operated equipment and the origin of AC-DC jokes (another topic). 
Around 1965, I visited the roundhouse of the Duluth, Missabe, and Iron Range Railroad in Proctor, MN, which still had one or two Yellowstone 2-8-8-4 simple articulated steam locomotives (the most powerful ever built, slightly more tractive effort than the more famous Big Boys of the Union Pacific).  The big electric motors ran on 25 Hz power for historical reasons, which they could still obtain from Minnesota Power and Light Co., although the rest of us enjoyed modern 60 Hz power.

Wasn't the U.S. still using DC for some TRAMS for quite a while??
Also, until recently seeing a "Mr. Carlsons Lab" radio restoration video, where it had an extra large transformer, designed to work down to 25-hz supply frequency, had I ever HEARD of the use of 25-hz !!

Also, to rsjsouza, regarding Earthing. I don't know how 'Earths' are set up in the U.S., but here in Australia, it goes like this...  The 'Earth' is not supplied to the property. An Earthing stake is driven into the ground close to the Switchboard/Meterboard. All the earth wires within the property (outlets/lights) go back to a dedicated earth-termination bar in the main switchboard. The Earth-stake in the ground is also connected to this bar. However, 'we' ALSO have a hefty cable link in the switchboard, linking that Earth-Bar to the Neutral-Bar, under what we call 'M.E.N.', meaning a 'Mains-Earth-Neutral' system. So that the Neutral is always referenced to Earth also!  Often, old un-earthed circuits simply need the addition of a separate earth wire, (if not included in the cables), to bring it up to spec. And we 'virtually' have no power outlets without a built in switch, which obviously switches the Active. And our outlets are automatically 'polarized' due to the diagonal layout of the prongs.   

[rsjsouza]

Also, to rsjsouza, regarding Earthing. I don't know how 'Earths' are set up in the U.S., but here in Australia, it goes like this...  The 'Earth' is not supplied to the property. An Earthing stake is driven into the ground close to the Switchboard/Meterboard. All the earth wires within the property (outlets/lights) go back to a dedicated earth-termination bar in the main switchboard. The Earth-stake in the ground is also connected to this bar. However, 'we' ALSO have a hefty cable link in the switchboard, linking that Earth-Bar to the Neutral-Bar, under what we call 'M.E.N.', meaning a 'Mains-Earth-Neutral' system. So that the Neutral is always referenced to Earth also!  Often, old un-earthed circuits simply need the addition of a separate earth wire, (if not included in the cables), to bring it up to spec. And we 'virtually' have no power outlets without a built in switch, which obviously switches the Active. And our outlets are automatically 'polarized' due to the diagonal layout of the prongs.   

Glenn, the standard here varies a lot around the country - since I don't work in the professional electrician field, I wouldn't risk throwing my inaccurate hints.

In my house I have a ground wire being fed to the panel, but I didn't pay attention if there is a connection to a bar near my meter - it could be done that way or perhaps there is a larger ground bar in the neighbourhood. Overall it seems the ground connection is alright as no tingling sensation happens with grounded chassis and no equipment was ever damaged due to lightning (and there is a LOT of lightining where I live).

[TimFox]

... Consolidated Edison in New York finally ceased DC distribution totally in 2007. ...

To be fair to Con Ed, I think they carried on with DC service for such a long time because there were a few elevators in NYC that used DC motors.  Substituting AC motors and controls was apparently deemed to be a bigger problem than just continuing DC service to the few ancient DC installations.
A search brought this article:
https://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/

Apparently the hold outs haven't converted to AC. They just installed AC to DC converters on site.

Yes, the very late dropping of DC service in New York was related to elevators.  However, before the War, there was a lot of DC distribution in New York and Boston, a big problem for transformer-operated equipment and the origin of AC-DC jokes (another topic). 
Around 1965, I visited the roundhouse of the Duluth, Missabe, and Iron Range Railroad in Proctor, MN, which still had one or two Yellowstone 2-8-8-4 simple articulated steam locomotives (the most powerful ever built, slightly more tractive effort than the more famous Big Boys of the Union Pacific).  The big electric motors ran on 25 Hz power for historical reasons, which they could still obtain from Minnesota Power and Light Co., although the rest of us enjoyed modern 60 Hz power.

Wasn't the U.S. still using DC for some TRAMS for quite a while??
Also, until recently seeing a "Mr. Carlsons Lab" radio restoration video, where it had an extra large transformer, designed to work down to 25-hz supply frequency, had I ever HEARD of the use of 25-hz !!

Third-rail subway, elevated, and suburban trains in US are usually DC (about 600 to 750 V) and originally ran with DC brushed motors for speed control.  Modern cars use inverters driving induction motors at variable frequency for speed control.  Overhead wires are often higher voltage DC;  the Illinois Central suburban line in Chicago uses 1500 V DC.  For  mainline service, the Pennsylvania RR electrified at 12 kV, 25 Hz, as a compromise between weight of control transformers in locomotives and DC motors driven by AC.  (Similarly, the Swiss railways used 16-2/3 Hz, a subharmonic of 50 Hz.)

[james_s]

Third-rail subway, elevated, and suburban trains in US are usually DC (about 600 to 750 V) and originally ran with DC brushed motors for speed control.  Modern cars use inverters driving induction motors at variable frequency for speed control.  Overhead wires are often higher voltage DC;  the Illinois Central suburban line in Chicago uses 1500 V DC.  For  mainline service, the Pennsylvania RR electrified at 12 kV, 25 Hz, as a compromise between weight of control transformers in locomotives and DC motors driven by AC.  (Similarly, the Swiss railways used 16-2/3 Hz, a subharmonic of 50 Hz.)

Wasn't the low frequency AC used so they could run large rotary converters back before mercury arc and later solid state rectifiers capable of handling high power levels were developed?

[jogri]

Similarly, the Swiss railways used 16-2/3 Hz, a subharmonic of 50 Hz.

Actually, germany, denmark and austria also use this system... It's a relict from the early 20th century, but it still works (some german powerplants even have dedicated 16 2/3Hz generators for that purpose). Btw, we even have a 400V three-phase suspension railway over here, i'd like to know which engineer envisioned this monstrosity (he was probably bored and decided he needed a new challenge).

[CatalinaWOW]

Whether totally factual or not, we were taught at university that all of the early power operating frequency decisions were actually fact based.  The analysis was presented and variations given in homework problems and tests.  They had a specific set of materials available at the time which set core losses in the transformers and also saturation levels.  Each system had an expected distribution architecture which set line losses through capacitance.  Set up the equations, take the derivative, find the zero point and you have the optimum frequency.  And with the data available to us at the time it appeared that the calculations were done correctly.  The difference between the European and North American solution is well with what would be expected from slightly different material costs and distribution arrangements.  And you would expect the distribution arrangement to be very different in a dedicated rail power system, so the frequency is significantly different (as is the frequency chosen for airborn and ship power systems). 

Once a few were built the benefits of standardization outweighed the benefits of optimization and folk settled on just a few options.

[Electro Detective]

Also, to rsjsouza, regarding Earthing. I don't know how 'Earths' are set up in the U.S., but here in Australia, it goes like this...  The 'Earth' is not supplied to the property. An Earthing stake is driven into the ground close to the Switchboard/Meterboard. All the earth wires within the property (outlets/lights) go back to a dedicated earth-termination bar in the main switchboard. The Earth-stake in the ground is also connected to this bar. However, 'we' ALSO have a hefty cable link in the switchboard, linking that Earth-Bar to the Neutral-Bar, under what we call 'M.E.N.', meaning a 'Mains-Earth-Neutral' system. So that the Neutral is always referenced to Earth also!  Often, old un-earthed circuits simply need the addition of a separate earth wire, (if not included in the cables), to bring it up to spec. And we 'virtually' have no power outlets without a built in switch, which obviously switches the Active. And our outlets are automatically 'polarized' due to the diagonal layout of the prongs.   

afaik the incoming 'Neutral' is also earthed via the power pole transformer box to an earth ground in the soil below

so the Neutral comes into the mains switchboard sort of 'pre-earthed' 

the premises 'earthing stake/copper plated rod' is wired to its own earthing buss bar

which in turn is then linked via a thick wire/link to the Neutral buss bar

If you lose the neutral, or any neutral, things still work via the earth return paths, but not safe 


Open for correction on this,
stubborn humming coffee machine undergoing diagnosis, dis-assembly and blockage purge/clean   

[vk6zgo]

... Consolidated Edison in New York finally ceased DC distribution totally in 2007. ...

To be fair to Con Ed, I think they carried on with DC service for such a long time because there were a few elevators in NYC that used DC motors.  Substituting AC motors and controls was apparently deemed to be a bigger problem than just continuing DC service to the few ancient DC installations.
A search brought this article:
https://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/

Apparently the hold outs haven't converted to AC. They just installed AC to DC converters on site.

Yes, the very late dropping of DC service in New York was related to elevators.  However, before the War, there was a lot of DC distribution in New York and Boston, a big problem for transformer-operated equipment and the origin of AC-DC jokes (another topic). 
Around 1965, I visited the roundhouse of the Duluth, Missabe, and Iron Range Railroad in Proctor, MN, which still had one or two Yellowstone 2-8-8-4 simple articulated steam locomotives (the most powerful ever built, slightly more tractive effort than the more famous Big Boys of the Union Pacific).  The big electric motors ran on 25 Hz power for historical reasons, which they could still obtain from Minnesota Power and Light Co., although the rest of us enjoyed modern 60 Hz power.

Wasn't the U.S. still using DC for some TRAMS for quite a while??
Also, until recently seeing a "Mr. Carlsons Lab" radio restoration video, where it had an extra large transformer, designed to work down to 25-hz supply frequency, had I ever HEARD of the use of 25-hz !!

Also, to rsjsouza, regarding Earthing. I don't know how 'Earths' are set up in the U.S., but here in Australia, it goes like this...  The 'Earth' is not supplied to the property. An Earthing stake is driven into the ground close to the Switchboard/Meterboard. All the earth wires within the property (outlets/lights) go back to a dedicated earth-termination bar in the main switchboard. The Earth-stake in the ground is also connected to this bar. However, 'we' ALSO have a hefty cable link in the switchboard, linking that Earth-Bar to the Neutral-Bar, under what we call 'M.E.N.', meaning a 'Mains-Earth-Neutral' system. So that the Neutral is always referenced to Earth also!  Often, old un-earthed circuits simply need the addition of a separate earth wire, (if not included in the cables), to bring it up to spec. And we 'virtually' have no power outlets without a built in switch, which obviously switches the Active. And our outlets are automatically 'polarized' due to the diagonal layout of the prongs.   

The Melbourne trams (streetcars) use DC, as did the long extinct Sydney & Perth ones.
For many years, Perth had a sustantial network of trolleybuses, which also used DC.

In the Sydney CBD, several old buildings were an "island" of DC into the 1950s, one strangely, being the headquarters of Australia's then premium Electronics magazine "Radio & Hobbies", (later "Radio,Television & Hobbies", then "Electronics Australia").

To provide ac for their design lab, & for anything else that needed it, there were "rotary converters" in the basement.
Unfortunately, there were power outlets of both "species" of electricity in the lab, so they occasionally let large quantities of "magic smoke" out of something.

The main reason for retaining DC was for the "Lifts"(elevators)

Later, the setup was reversed, with AC to the building, but rectifiers in the basement for the lifts.
Later, still, it was becoming obvious that the old lifts couldn't meet modern safety standards, & parts were virtually unobtainable, so building management "bit the bullet" & replaced them with modern ones.

[schmitt trigger]

I know that New York’s subway, Paris metro and others still use DC. But how about London’s tube?

[TimFox]

I have not seen a reference to this, but I believe train cars with sliding power contacts to DC feed (third rail or overhead wire) use capacitors on the vehicle to mitigate rough connection.

[Gyro]

I know that New York’s subway, Paris metro and others still use DC. But how about London’s tube?

Yes, 600V DC irrc. The London tube actually has a fourth (centre) rail. It returns current through this insulated rail, rather than the running rails, to prevent corrosion of surrounding metal structures, pipes, etc.

UK suburban 3rd rail systems are also 600V DC. They used to use mercury arc rectifiers, I don't know about these days.


In days gone past, the London underground had its own coal fired power station near the Thames, the coal was stored under water to prevent spontaneous combustion (funny how you remember little facts like that), but these days the supply is derived from the grid, with a gas turbine powered backup station.

P.S. There used to be nothing better than watching the 3rd rail slippers on a train sparking violently on a really cold, frosty morning (school day memories!). I suppose it's all VFDs these days, but back then, it was brushed DC motors and stepped resistor current controllers.

[TimFox]

The Chicago Transit Authority retired the last 6000 series ‘L’ cars in 1992, after 42 years of service.  IIRC, there were three forward settings on the speed lever:  resistor, series, and parallel (fastest).  Until VF drives, DC motors were the practical choice for variable speed.