Test Equipment Anonymous (TEA) group therapy thread

[Specmaster]

IMO only time served sparkies should be allowed to inspect/sign off works. Doesn't guarantee competence, but increases the probability at least.

At least I managed to -1 my repair queue in amongst the arguments yesterday. My Fluke 8060A is now fully functional, and without warming up the calibrator for a full check, it seems bang on so far. More details in Discord later.

I  won't be on discord again tonight, still involved in bedroom decorating, after about 7 match pots, settled on a colour, purchased the paint and painted the room. Problem is that the colour when dried was different to the match pot and not suitable, Finally found the right colour  and now need to crack on again before the new bed gets delivered 

[Vince]

Well, one more TDS754D scope lives to see another day. It's working quite well.

Another is on the bench now, trying to figure out why the display has decided to go black and white, even after replacing the CRT, CRT PCB and the main processor board one by one... It was colour then it wasn't.   

Looks like a problem with the LCD shutter then ? Maybe damaged... that's what gives the colours to the CRT...

[Vince]

VARTA Battery :

OK it's been resting for 24H now, so I just measured the voltage again : it settled for 9.4V . Was 10.3 just after charging, and down to 9.75V just 5 minutes later. So it was quickly going for it's final state.

OK so now it's had its first full slow charge since 30 years of storage... discharge it slowly now ? Using my adjustable current source or just sticking a resistor across it ?

I guess it does not matter, as long as current is reasonable. So I will go for C/10 again, and check back on it in 10+ hours.

C/10 is fine  just don't let it get below 7V (1V per cell).
It looks like it has survived. it long sleep. A couple of slow discharge and chare cycles should brng the capacity up.
This is routine maintenence on ni-cads used on aircraft. On most aircraft batteries you have access to individual cell connections (even small packs with D cells). For a capacity recovery and cell balance You discharge until the first cell reaches 1V then clip a 1 ohm resistor across that cell. This continues to discharge the cell but stops it being reverse charged by the main battery discharge current. Next cell to 1V  clip a resistor o and so on.  If the voltage of a cell goes below 0.5V whill still discharging the whole battery the resistor is replaced with a shorting clip. When about 50% of cells are at 1V a 1 ohm goes cross each cell and total battery discharge turned off. Typically leave overnight at this point. Then all cells have shorting clip and left for a day. Clips remved, left for nother 12H before bing put on a C10 charge. capacity chcek and re-charge.
Seems a lot of bother but the batteries are very expensive. Individual failed cells can be replaced. When I started this was all done manually including motitoring and adjusting the current with a rheostat. Now they make fully automatic systems. And batteries are slowly moving to Lithium.

Interesting, thanks for that ! 

Just plugged the battery to the current source to discharge it.
Took two attempts... my first idea of how I should connect the battery to Sir Wilson to discharge it, was not successful, zero current registered.
Then tried something else and it appears to work... see pics / schematics below, and have a good laugh if so you must... I can take it.
Bench DMM is monitoring battery current, and the analog meter monitors battery voltage.

So loaded with C/10 ie 11 mA, as planned.  That made the battery voltage go down to 8.8V at first, then after 30 minutes or so... it's down to 8.6V, so is sinking fast eh ?  Hmmm...... not looking too promising, but we shall see how it goes ! 

Will do a second charge/discharge cycle regardless. It sat for 30 years so it deserves some kindness on my part ! 


EDIT : Oops my bad !  Wiring is messy, the schematic originally showing what I THOUGHT I had done to get it to work... was incorrect. Apologies to those who looked at it.  Schematic corrected / re-uploaded.

In the end there is no messing around required... battery is simply connected up as if it were any regular load, between the output of the mirror, and ground, just with the positive terminal connected to ground.
So I was just overthinking it, it's all very simple in fact !     Only thing is that I messes up the adjustment range. With no load , i.e the the mirror short -circuited, range was as I said earlier, 3.7mA up to 13.5mA IIRC. Now with an active load such as this battery, range is about 4.7mA up to 22mA. So a wider excursion.

EDIT #2 : Oh, and the joys of making experiments in a controlled environment..... let's do something cool shall we ? What is the output impedance of a 30 year old NiCd 9V battery when it spits a few mA ?

Since I can adjust the current at will, and watch battery voltage at the same time, it's easy to do ! At least a decent approximation of it.  So :

At 20mA battery voltage is 8 Volts.
At 7mA it's 8.4V.

So a 0.4V drop for a 13mA increase in current. If I have my PhD maths right, then that's about 30 ohms. How good is that, any idea ? Sounds a bit high to me ? Maybe the battery did degrade over the 30 years after all...   We shall measure again when we do the second discharge/discharge cycle tomorrow.

[mnementh]

IMO only time served sparkies should be allowed to inspect/sign off works. Doesn't guarantee competence, but increases the probability at least.

I agree... however, then you have the problem of aging homes like this one, where we've been through essentially at least a half-dozen major revisions to the electrical code. To refit the whole house to current code would, in this case, require some pretty extensive demolition/remodeling.

It's really a horrible double-bind, particularly given the expense of hiring a decent & licensed electrician due to the cost of staying certified, liability/accidents & omissions insurance, and even, in some locations, requirement to have separate workman's comp as the electrician is their own employer.

I can get that it's unreasonable to try and apply Industrial-grade electrical standards to a near-century-old private residence; but fuck... there should be some better middle ground where this work can be done without mortgaging the next 3 generations.

mnem
dwagon caught in the middle*

Here at least if something was compliant with the current code at time of installation, it doesn't have to be replaced until it's no longer serviceable.

Heading off to Discord, which is quite harmonious, ironically enough...

Well, its that no longer serviceable part that's the real dicksore, innit...? 

One can reasonably argue that cloth-insulated wire was never really serviceable... but here we are with homes all over New England fulla the stuff.

mnem
 

[VK5RC]

@mnem - so hard to know when to stop - especially as it is not really your problem but you want to keep it reasonably safe.

Some years ago - a house I bought (built approx 1890) - had proper wiring to the power outlets ( Aus romex equivalent and even a GFCI) - I foolishly assumed that the lighting circuits were as well! Finally after getting into the roof space I discovered an electrical museum piece - cloth covered wire in wood slats FFS! Here in Aus you are supposed to have all fixed wiring done by certified electrician and a certificate of compliance. The 'sparky' I got offered a good discount if I was his 'grunt' ie did most of the dirty work. I didn't mind because of the price but also a happy tradesman generally does better work.
In Aus I have never seen a wire nut used - almost always a hard mounted terminal block with cover or a loose one with insulated cover for inside wall boxes etc.

[bitseeker]

To continue on the HP tube goodness, I scanned back to this video's date and didn't see it posted here already, so here we go:

[Neper]

Some years ago - a house I bought (built approx 1890) - had proper wiring to the power outlets ( Aus romex equivalent and even a GFCI) - I foolishly assumed that the lighting circuits were as well! Finally after getting into the roof space I discovered an electrical museum piece - cloth covered wire in wood slats FFS!

At least yours was isolated. The mother of a friend had a beautiful villa in the North of France, built around 1900, where everything still was original in the late 1980s. Gas, water, electricity... the lot. In the basement, the lines for the lighting were made of bare aluminium wires, about 2 mm thick, mounted below the ceiling on little porcelain spacers at a height of 1.90 m at best. You could have run a little trolley bus down there. :-)

No idea what the original voltage was, supposedly 100 volts DC or so, but with 230 V AC this was one of the most hair-raising things I've ever seen.

[AVGresponding]

IMO only time served sparkies should be allowed to inspect/sign off works. Doesn't guarantee competence, but increases the probability at least.

I agree... however, then you have the problem of aging homes like this one, where we've been through essentially at least a half-dozen major revisions to the electrical code. To refit the whole house to current code would, in this case, require some pretty extensive demolition/remodeling.

It's really a horrible double-bind, particularly given the expense of hiring a decent & licensed electrician due to the cost of staying certified, liability/accidents & omissions insurance, and even, in some locations, requirement to have separate workman's comp as the electrician is their own employer.

I can get that it's unreasonable to try and apply Industrial-grade electrical standards to a near-century-old private residence; but fuck... there should be some better middle ground where this work can be done without mortgaging the next 3 generations.

mnem
dwagon caught in the middle*

Here at least if something was compliant with the current code at time of installation, it doesn't have to be replaced until it's no longer serviceable.

Heading off to Discord, which is quite harmonious, ironically enough...

Well, its that no longer serviceable part that's the real dicksore, innit...? 

One can reasonably argue that cloth-insulated wire was never really serviceable... but here we are with homes all over New England fulla the stuff.

mnem
 

It is, until it isn't...

[tautech]

IMO only time served sparkies should be allowed to inspect/sign off works. Doesn't guarantee competence, but increases the probability at least.

I agree... however, then you have the problem of aging homes like this one, where we've been through essentially at least a half-dozen major revisions to the electrical code. To refit the whole house to current code would, in this case, require some pretty extensive demolition/remodeling.

It's really a horrible double-bind, particularly given the expense of hiring a decent & licensed electrician due to the cost of staying certified, liability/accidents & omissions insurance, and even, in some locations, requirement to have separate workman's comp as the electrician is their own employer.

I can get that it's unreasonable to try and apply Industrial-grade electrical standards to a near-century-old private residence; but fuck... there should be some better middle ground where this work can be done without mortgaging the next 3 generations.

mnem
dwagon caught in the middle*

Here at least if something was compliant with the current code at time of installation, it doesn't have to be replaced until it's no longer serviceable.

Heading off to Discord, which is quite harmonious, ironically enough...

Well, its that no longer serviceable part that's the real dicksore, innit...? 

One can reasonably argue that cloth-insulated wire was never really serviceable... but here we are with homes all over New England fulla the stuff.

mnem
 

It is, until it isn't...

Still have a couple of runs of cotton covered conduit wire here but as it's in steel conduit tube which doubles as the PE it's quite safe.
However the old rubber covered twin and bare PE cable is quite another matter and a common house fire starter now the stuff is 70+ years old. 
That muck needs be replaced !

[tggzzz]

Some years ago - a house I bought (built approx 1890) - had proper wiring to the power outlets ( Aus romex equivalent and even a GFCI) - I foolishly assumed that the lighting circuits were as well! Finally after getting into the roof space I discovered an electrical museum piece - cloth covered wire in wood slats FFS!

I saw that under the floorboards of my parent's house, back in the early 80s. Fortunatelty it wasn't connected.

Worse was a later variant where the external sheath was neither plastic nor rubber nor wood: it was lead, and acted as the earth (allegedly). Junctions were made by a metal box which gripped (loosely) the  (oxidised) lead sheath. Not connected, fortunately.

Their current house, built 1847, has rubber wires to round-pin plugs. Again, not connected, but the next owner will have to completely rewire the house to insert RCBs - and the house is Grade II listed which means works and reparations have to be "authentic".

[Specmaster]

@mnem - so hard to know when to stop - especially as it is not really your problem but you want to keep it reasonably safe.

Some years ago - a house I bought (built approx 1890) - had proper wiring to the power outlets ( Aus romex equivalent and even a GFCI) - I foolishly assumed that the lighting circuits were as well! Finally after getting into the roof space I discovered an electrical museum piece - cloth covered wire in wood slats FFS! Here in Aus you are supposed to have all fixed wiring done by certified electrician and a certificate of compliance. The 'sparky' I got offered a good discount if I was his 'grunt' ie did most of the dirty work. I didn't mind because of the price but also a happy tradesman generally does better work.
In Aus I have never seen a wire nut used - almost always a hard mounted terminal block with cover or a loose one with insulated cover for inside wall boxes etc.

Years ago I first stumbled upon this cloth covered wire quite by accident, I was working as a factory maintenance engineer, the only one at this factory which was part of the GEC company, the company was called L P Foreman & Son Ltd. It produced all the special shipping containers for the English Electric Valve Co, Marconi Radar, Marconi Marine and Marconi Telecommunications, and these containers were really something special, designed to transport giant broadcasting valves, Radar, and transmitters for both radio and television etc to any part of the globe, across any terrain without suffering any damage, and some of those valves were massive and were worth millions. I was in charge of everything, electrical, mechanical, pneumatics, wood working machinery, plumbing, buildings, fork lifts, and overhead cranes.

Anyway, the MD of said company had a beautiful oak panelled office, even the ceiling was oak panelled, in the main office. One day the light switch failed, when I removed the locking ring holding the faceplate on, I was met with the spectacle of the switch recessed behind oak panelling and totally exposed cables connected to the switch. I had no alternative but had to start pulling the oak panelling apart, which displeased the MD, but there was nothing else I could do. I was then met with the wood capping, with 2 wires about 25 mm apart protruding from it, all insulation on the cables had gone. Showing this to the MD, he then gave me immediate permission to remove all the panelling and update the wiring throughout the office complex. The cabling was the old VIR cable (vulcanised Indian Rubber) single core wrapped in a cotton sheath, hence why some call it cloth covered, and the more I pulled the capping cover off, the more of the perished and rotten cable insulation and covering fall of the inner cores.

So then it just me and my apprentice had to tackle the job over the next few months between us, and we uncovered many horrors along the way, lead cables, rubber, VIR cleat wiring and capping hidden behind oak panels, some of which had been painted over the years.

After we also between us, rewired the entire factory site and discovered some horror stories there as well, including many fore planners and other specialised machines that been completely wired in ground cables (green and yellow), not just the mains supply, but the controls for them as well had been done the same by the person whom I took over from when he retired 

Just how the hell did people like that, with no qualifications, get to be given a position like that is beyond me.

The site is now part of a housing estate but the old office complex still stands and can be shown in the attached aerial photo, (the grey roofs in a C shape, the rest was a mixture of buildings and massive wood yard and crane.)

[Vince]

Interesting, thanks for that ! 

Just plugged the battery to the current source to discharge it.
Took two attempts... my first idea of how I should connect the battery to Sir Wilson to discharge it, was not successful, zero current registered.
Then tried something else and it appears to work... see pics / schematics below, and have a good laugh if so you must... I can take it.

EDIT : Oops my bad !  Wiring is messy, the schematic originally showing what I THOUGHT I had done to get it to work... was incorrect. Apologies to those who looked at it.  Schematic corrected / re-uploaded.

In the end there is no messing around required... battery is simply connected up as if it were any regular load, between the output of the mirror, and ground, just with the positive terminal connected to ground.
So I was just overthinking it, it's all very simple in fact !     Only thing is that I messes up the adjustment range. With no load , i.e the the mirror short -circuited, range was as I said earlier, 3.7mA up to 13.5mA IIRC. Now with an active load such as this battery, range is about 4.7mA up to 22mA. So a wider excursion.

No no no no.... no.

I am starting to think... uh.... I am doing rubbish I think ! 

I bet this circuit is not discharging the battery at all... sure I can see the current going out the battery is 111mA as wanted, however I fear this current is supplied by the lab power supply, not the battery per se... I mean the battery is basically "transparent" ... every electron coming out of it is being put back on the other side by the lab supply, isn't it ?  It's neither being charged or discharged, it's status quo...

That's why I came up with my first schematic earlier, where the mirror is supplied with the voltage of the battery itself rather than lab supply... but alas it does not work.

I think I am doing rubbish, though it's interesting as a learning experience... gets one thinking and hopefully makes him that bit less stupid at the end of it.

Si I think the simplest and most reliable way to discharge this battery... is simply to stick a resistor across it.... 

However I think that for the CHARGING cycle, the current source should work fine...


Where are the TEA engineers when you need them ??     They are sleeping of course, it's 1AM....

[AVGresponding]

@mnem - so hard to know when to stop - especially as it is not really your problem but you want to keep it reasonably safe.

Some years ago - a house I bought (built approx 1890) - had proper wiring to the power outlets ( Aus romex equivalent and even a GFCI) - I foolishly assumed that the lighting circuits were as well! Finally after getting into the roof space I discovered an electrical museum piece - cloth covered wire in wood slats FFS! Here in Aus you are supposed to have all fixed wiring done by certified electrician and a certificate of compliance. The 'sparky' I got offered a good discount if I was his 'grunt' ie did most of the dirty work. I didn't mind because of the price but also a happy tradesman generally does better work.
In Aus I have never seen a wire nut used - almost always a hard mounted terminal block with cover or a loose one with insulated cover for inside wall boxes etc.

Years ago I first stumbled upon this cloth covered wire quite by accident, I was working as a factory maintenance engineer, the only one at this factory which was part of the GEC company, the company was called L P Foreman & Son Ltd. It produced all the special shipping containers for the English Electric Valve Co, Marconi Radar, Marconi Marine and Marconi Telecommunications, and these containers were really something special, designed to transport giant broadcasting valves, Radar, and transmitters for both radio and television etc to any part of the globe, across any terrain without suffering any damage, and some of those valves were massive and were worth millions. I was in charge of everything, electrical, mechanical, pneumatics, wood working machinery, plumbing, buildings, fork lifts, and overhead cranes.

Anyway, the MD of said company had a beautiful oak panelled office, even the ceiling was oak panelled, in the main office. One day the light switch failed, when I removed the locking ring holding the faceplate on, I was met with the spectacle of the switch recessed behind oak panelling and totally exposed cables connected to the switch. I had no alternative but had to start pulling the oak panelling apart, which displeased the MD, but there was nothing else I could do. I was then met with the wood capping, with 2 wires about 25 mm apart protruding from it, all insulation on the cables had gone. Showing this to the MD, he then gave me immediate permission to remove all the panelling and update the wiring throughout the office complex. The cabling was the old VIR cable (vulcanised Indian Rubber) single core wrapped in a cotton sheath, hence why some call it cloth covered, and the more I pulled the capping cover off, the more of the perished and rotten cable insulation and covering fall of the inner cores.

So then it just me and my apprentice had to tackle the job over the next few months between us, and we uncovered many horrors along the way, lead cables, rubber, VIR cleat wiring and capping hidden behind oak panels, some of which had been painted over the years.

After we also between us, rewired the entire factory site and discovered some horror stories there as well, including many fore planners and other specialised machines that been completely wired in ground cables (green and yellow), not just the mains supply, but the controls for them as well had been done the same by the person whom I took over from when he retired 

Just how the hell did people like that, with no qualifications, get to be given a position like that is beyond me.

The site is now part of a housing estate but the old office complex still stands and can be shown in the attached aerial photo, (the grey roofs in a C shape, the rest was a mixture of buildings and massive wood yard and crane.)

Sounds like a fine adventure!

[xrunner]

So then it just me and my apprentice had to tackle the job over the next few months between us, and we uncovered many horrors along the way, lead cables, ...

Lead cables? Well I had never heard of that before. Can you describe these a little more if you remember? So heavy - how were they encased?

[mnementh]

...I think the simplest and most reliable way to discharge this battery... is simply to stick a resistor across it.... 

You had the right idea, in that you want to keep it discharging at a constant current so you can calculate mAH.



Since you don't own one of these      (it probably wouldn't serve you very accurately due to its own current draw anyways), I'd suggest a 7805 in constant-current mode, or even simpler, a AMS1117 (variable set around 3-4V or AMS1117-3.3 fixed) driving a LED at approx 5-10mA through a pot; set the LED drive such that total current draw is ~0.1C/11mA, or as close as you can get and have a stable current draw.

Just remember that these have 5-8mA quiescent current on top of the LED drive. There are a lot of newer linear regs that have lower quiescent current, but I was looking for something you might likely be able to scrounge off a old PCB, like the AMS1117-3.3 which is nigh-ubiquitous.

This is an approach I've used in the past for dumping RC batteries; I've never tried it on anything this low-current before, so YMMV, etc...

Good hunting!

mnem
 

[Vince]

Oh yeah didn't think of that... Wilson mirror came to mind first, and is much more cool than a bloody 7805 but... less room for error for a dummy like me with the latter... so might try that.

So here I would put the battery at Vin, and short Vout so the 7805 can get the set constant current to flow ?

In the meantime, I have just wired this simple but ultra reliable circuit. It's constant current for now as battery is holding up !
Rob said no less than 7 Volts, at which point current will be about 8.5mA. So still not far off 10mA. So I didn't really need a constant current thing to DIS charge eh.... will be really useful only when REcharging the thing.. at which point my Wilson should work fine I think ! 

If not.... that will be a 7805...

[Specmaster]

So then it just me and my apprentice had to tackle the job over the next few months between us, and we uncovered many horrors along the way, lead cables, ...

Lead cables? Well I had never heard of that before. Can you describe these a little more if you remember? So heavy - how were they encased?

Well, we in the UK use flat T&E (twin and earth cable, 2 cores plus earth or ground cable) so to look at the lead sheathed cable was much the same but tended to be 2 core cable as the lead sheath was clamped to the switch etc and effectively was grounded via the lead. Yes it was very heavy, and it was clipped using the good old-fashioned metal buckle clips that ere secured by way of a nail through the central hole and then the cable was placed over the nail and the clip wrapped around the tab, poked through the eye and folded back on itself to secure the cable in place as shown in the attached.

[Brumby]

It's amazing what you hear - even when you aren't listening.....


I was up late last night, fettling at my desk with the TV providing some noise.  There was some nondescript show on and I ignore these types of show with the appropriate amount of apathy for the "quality" of programming that they offer.  Ask me later what the show was about and I would likely respond with "What show?"

However, completely engrossed in what I was poking around, my attention was immediately grabbed by the phrase "1972 Oscilloscope" which clearly penetrated my bubble of indifference to the outside world.  I quickly hopped up to see what this device could be only to see it for less than half a second.  As I watched, they never went back to it.

Nevertheless, I just had to know what the scope was - so I tracked down the show and registered for the TV station's online service so I could see the show ... and I was able to get this shot of the scope:



I can't remember EVER seeing an oscilloscope featured on TV before - for it's own sake.  Yes, lots of times as set decoration, but never like this.

[Zucca]

It's... MS-DOS 11.11 !!! 
mnem

Oh yeah, no icons, no animations, no wankery, no teenagers, no Cortana, no Edge, nothing.
Pure speed.

I would love a smartphone in terminal...

PS: Linux I soon I will be there...

[Vince]

It's amazing what you hear - even when you aren't listening.....


I was up late last night, fettling at my desk with the TV providing some noise.  There was some nondescript show on and I ignore these types of show with the appropriate amount of apathy for the "quality" of programming that they offer.  Ask me later what the show was about and I would likely respond with "What show?"

However, completely engrossed in what I was poking around, my attention was immediately grabbed by the phrase "1972 Oscilloscope" which clearly penetrated my bubble of indifference to the outside world.  I quickly hopped up to see what this device could be only to see it for less than half a second.  As I watched, they never went back to it.

Nevertheless, I just had to know what the scope was - so I tracked down the show and registered for the TV station's online service so I could see the show ... and I was able to get this shot of the scope:



I can't remember EVER seeing an oscilloscope featured on TV before - for it's own sake.  Yes, lots of times as set decoration, but never like this.

Wow cool but... do you mean you PAID to get access to that show just to see the scope ?! 
You must be rich ! 

So what kind of show was it then ?

The kind of show where people have to guess the price of items, and the guy that's closest to the price wins something ??
Or maybe the kind of show where people bring their old stuff and a panel of antique dealers bid on it and the guy makes some money this way ?

Do tell... you wet our appetite now... you can't let us down...

[Zucca]

posted here:
https://www.eevblog.com/forum/chat/22-year-old-builds-chips-on-his-garage/

at the end nice shots of TEA.
https://youtu.be/IS5ycm7VfXg?t=303

[cyclin_al]

And so... here I am, on the other side...   After several rounds of poking around dusty, cobweb-entangle floor joists and crawlspaces, I finally figured this crazy little bastard out. <snip> But now comes a whole new misery: Each half of this duplex is connected to a different breaker. Thankfully, both on the same rail so no 240V differential, but I don't know of any GFCI outlet that'll do 2 circuits in one duplex.

That would be SO "illegal" in that it violates the assumption of least surprise. Not illegal per se: I just spent some time reading the swedish law, and the by public administration released regulations, that are binding like law, just easier to change.  If you deviate from the Swedish standards (which are neither law, nor regulations) you must document how, why and when the deviation was made, and I guess you must motivate why.

A duplex outlet in Sweden, by design, never can be wired separately; there are bars connecting the two receptacles. A quadruple can, but it is frowned upon.

I would put up two quadruples (in boxes, not recessed), one per circuit, mark them as such and be done with it. That would be least surprising, which is a Good Thing. This being a rental, I'm quite aware of your hands being tied at times, but at least here, the responsibility of the contractor (by law! this is what the law mostly is concerned with) is such that they will sometimes be forced to perform corrective actions on electrical installations to be free of liability.

I know I addressed this already, but...

The odds are that the contractor who did these is long-dead, and I believe at one time it was supposedly considered acceptable to use the box to connect the ground conductors as done here.

As for the outlet itself... I actually did have a wild hair notion to do something similar in a single oversized 2-gang box. But then I realized all the misery I could be in for if I made such changes, and decided it was better to limit my own personal exposure.

mnem
 

Doing something with a 2-gang box was one of my initial thoughts as well, which I will not bother to describe now.  What I was thinking does NOT match Dwagon's scenario.

Here in the GWN, it is common to make one receptacle switched as Dwagon described. 
However, we also have another scenario called "split receptacle" to provide MOAR POWER ... !  (In a normal circuit, the total circuit can only supply 15A at 120V.)
This was used typically in kitchens or workshops/garages where high-current appliances might be used.
On the duplex receptacle, the hot bus-bar tab could be snapped off to separate the two receptacles.
Then one receptacle would be wired Live1-N and the other would be wired Live2-N.  That allows you to plug in a 15A 120V appliance in EACH receptacle, which would appear to provide 30A.
It was sold as a cheap option, as it required only 3 conductors L1, L2 & N in a single cable (rather than using 4 conductors in two separate cables for L & N and L & N).
Back at the breaker panel, a 15A at 240V breaker would be used (again, cheaper than two 15A at 120V breakers).
As Dwagon mentioned earlier on this topic, it could be possible to see 240V at the receptacle if anything went wrong.
Common ways for it to go wrong involve water (like in a kitchen) or automatic dust collectors (that sense current in another circuit that supplies the tool).
Another way is connecting something powered by one 'side' of the circuit to something else powered on the other 'side' of the circuit in an electronics lab...

As an aside, I think I just gave myself an answer to my question back when Zucca and I were discussing differences between EU and NA breaker panels...
(in NA, choose breakers carefully and choose position in the breaker panel to avoid an unexpected 240V differential in the lab!)

Nowadays, the GFCI outlets do not work with the "split receptacle" scenario.  The most powerful option is to wire the GFCI duplex receptacle to a 15A at 120V breaker.  Actually, new construction has the GFCI protection built into the breaker (or arc fault AFCI or both together DFCI), rather than built into the receptacle.
People like my parents expect the "split receptacle" scenario so they get confused when they plug in two high-current appliances into the receptacle and wonder why the breaker tripped...

[TERRA Operative]

So then it just me and my apprentice had to tackle the job over the next few months between us, and we uncovered many horrors along the way, lead cables, ...

Lead cables? Well I had never heard of that before. Can you describe these a little more if you remember? So heavy - how were they encased?

In Australia you used to get lead sheathed telephone cables.
Paper wrapped conductors (IIRC) inside a lead tube. Always interesting to come across in older homes, the inner conductors were still copper so it was the usual story for terminations.

[TERRA Operative]

WINNER WINNER, CHICKEN DINNER! 


I decided to call it a night at 4am after losing colour across multiple CRT's/Shutters, CRT driver boards and main processor boards.
Came back today, put it together and it works! I must have forgotten something in my bleary eyed, 4am daze, but I can't remember what.... 

Now to run it through a few SPC self calibration procedures to check it doesn't fail and maybe update the firmware if the later 784D firmware will work. (It'll stay as a 754D for now, but firmware is common depending on board revisions. It's easy to flash and try and flash back if no-go, just time consuming).

[tautech]

So then it just me and my apprentice had to tackle the job over the next few months between us, and we uncovered many horrors along the way, lead cables, ...

Lead cables? Well I had never heard of that before. Can you describe these a little more if you remember? So heavy - how were they encased?

In Australia you used to get lead sheathed telephone cables.
Paper wrapped conductors (IIRC) inside a lead tube. Always interesting to come across in older homes, the inner conductors were still copper so it was the usual story for terminations.

We had those dry core paper wrapped cables in small towns in NZ some 40 years back and well remember a lightening strike very close to where I worked at the time on a phone pole just 40 yds away. Furk it went with a BANG !
Stuffed the shop phone and the alarm dialer and a good chunk of the lead outer dry core paper insulated telecom cable.
Looked at a section they cut out which had little arc holes in the paper all over. IIRC it was a 100 pair cable and it was a few days before we had a business phone again.