If I was in an underground cave I would rather have 30 lumens of warm high CRI light. I can understand the resistance to upgrading if you have gear that is well known (and well known flaws) vs. new stuff that needs testing and familiarising, and training others on use (health and safety).
The suspense is killing me. Someone guess this correctly now darn it.
I would guess some type of capacitor, but the sleeping with it under your pillow the first night thing is throwing me off. I can't imaging wanting to have a capacitor anywhere near my rock filled head. I wasn't playing with electronics much back then. So I have no appreciation for the shortage of this type of part.
I wasn't even born yet in 1971!
-Garry
I remember my much older sister telling me that until one goes deep down into the earth, they have NEVER seen darkness. Only then can you experience the total absence of light.
Another coincidence! Only last night I read this article. Huge Dark Matter Experiment Finds Nothing but More Mysteries | WIRED
How’s that for a LUX meter………and it’s buried in a cave.
It looks like a chassis mount capacitor, the kind used in output stage of power amps. Maybe you could get them cheaply because of transistor amps becoming more popular?
But you all have not answered every question. I am also hoping that someone will give us more than I am asking, stuff I didn’t know.
You nailed the manufacturer part of it! Here is another pic
There are a lot of reasons why they are no longer as necessary. What are they?
Computers, interesting idea.
But What happened in 1971?
Maybe a company switched from linear regulated PSUs to SMPS, rendering their stock of big caps useless?
Could be at that time.
Oh the suspense. 
Rated at 40 VDC they certainly are not for vacuum tube power supplies. Filter caps for B+ power supplies would be 470 volts or so.
I remember that in 1971 the HP hard disk drives that I worked on had big capacitors like that for emergency head retract in the event of power failure.
Back in the day, often times Amplifier manufacturers would would use huge non-polarized capacitors to protect the speakers from any DC current. Theoretically that would impact low end response. In my opinion the better designs wouldn’t need them. 2 of these in series in reverse polarity could mimic a non polarized capacitor. When that was done though, shunt resistors of the proper value had to be used. It was a kludge. My personal use was for filter capacitors in power supplies.
But around that time” things were a changin………………”
You are all going to figure it all out… and more…… I want to learn more too!
I have taken too a long a lunch break. I’ll be back later, until then I will leave you with a quote I just came across.
“Resistance is futile, but capacitance has potential”
Aluminum electrolytic capacitors with excellent initial electrical performance, voltage combinations, high current filtering, energy storage, and good ripple capability. High performance, high capacitance and high CV rated. The were/are used for spot welding, DC/DC converters of +500W power, DC/AC AC/AC +500W converters, motor starters, flashtube ignitors, audio crossovers, frequency converters, DC links, DC buffering, UPS buffering ….
How did you get such a good deal on them?
They are so big. Were they used in some kind of computer?
Hmm . . . in 1971 Intel released it's first microprocessor. Is this related? Death of main frames or something? I'm probably stuck on 1971, but the "event" could have happened earlier.
-Garry
Me too! I love learning about older technologies.
Hmm . . .
1968:
- The first computer with integrated circuits made.
-Garry
Did the introduction of super-capacitors cause a temporary drop in traditional capacitor prices? Is that how you came to having a one night stand with one of those caps?
Yep, one might consider mercury vapor rectifiers as light emitting diodes… they are diodes and they do emit light!
supercapacitors with activated carbon electrodes
The questions are:
What is it?
What was it called?
Where was this particular item to be used?
Bonus: Why was I able to get so many of them so cheaply? Hint: 1971
What is it? - a capacitor, you got that right away
What was it called? - They were commonly called Computer Grade Electrolytic Capacitors In fact in this picture there is a marking on the item “CGS” The CG I presume, stood for Computer Grade. The S designation meant that it wasn’t up to the highest of standards. Still a cut above other standards of the time.
Where was this particular item to be used? Of course I can’t be absolutely sure but probably in a main frame computer, and probably in a linear power supply.
Back in the late 60’s and early 70’s there was a 10 mile stretch of route 128 that had a high density of high tech companies. Also at that same time there was alot of changes taking place in the computer industry. garrybunk zeroed in on that in his investigations. allan d knows his parts and even guessed the manufacturer. dave_ realized that manufacturers were also going from linear power supplies to switching power supplies, which do not require such large filter capacitors.
Now the reason I was able to get them so cheap:
Back then, in the Boston area, there were all those high tech companies that were in the middle of a revolution in computer technology. Tech was advancing so fast and computers were becoming obsolete much sooner than they were ever expected to. I lived in Connecticut, in reasonably close proximity to Boston. At that time there was a lot of computer surplus available and there were quite a number surplus stores set up to dispose of it all. First of all, form a Wikipedia article on route 128, here is a list of some of the more well known companies in that area.
Digital Equipment Corporation
Data General
BBN Technologies
Thermo Electron and Fisher Scientific, later merged as Thermo Fisher Scientific
Analog Devices
Computervision
Microsoft
GTE
Honeywell Information Systems
MITRE
Polaroid
Sun Microsystems
BEA Systems
Turbine, Inc.
EMC Corporation
Autodesk
Raytheon
Wang Laboratories
Apollo Computer
Prime Computer
Cullinet
Most of these companies were main frame computer companies and did not survive the shift in computers.
On the surplus market there was literally TONS of surplus computers, parts, boards etc. for next to nothing.
To me it was a magical time. Every once and awhile I would leave Connecticut, and do the route. Go from surplus store to store, just looking in amazement at all the high quality stuff for cheap. Also at that time, in the same areas, there was a lot of vacant manufacturing space. Those buildings made perfect cheap warehouses for the surplus dealers.
I bought those capacitors at “Delta Electronics” in Amesbury, MA. The owner was a retired Engineer and his son owned the building he was in, and did not charge him any rent. The building was an old automobile manufacturing plant.
See, they even had electric cars in 1914, went 100 miles on a single charge!
Or so they said 
It was HUGE, and it was FULL. This guy had pallets and pallets of stuff, most never even gone through. I got friendly enough with him that he would let me rummage through and look for stuff. One visit, while rummaging, I found thousands of brand new capacitors, in boxes that were never opened. As I said earlier, capacitors were hard to come by and were very expensive. Also, there were no wall warts of switching power supplies as there are now. If you were going to build anything, you also had to build a power supply. That meant a transformer, some diodes and capacitors, big capacitors if you were going to draw any significant amount of current.
Anyway, I put my pile together and the time came to pay up. I told him about the hoard of capacitors that I found (I don’t think he even knew he had them) and asked him how much. This time instead of giving me a price, he looked me straight in the eye and said “you tell me”. I looked him straight back and said “5 bucks”
I could tell he was taken aback a little, but he said alright.