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why 12V?



 
 
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  #31  
Old March 8th 17, 07:06 PM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 404
Default why 12V?

On Wed, 8 Mar 2017 11:43:12 -0000, "NY" wrote:

"Graham." wrote in message
.. .
Why 6.3V for many valve heaters?

And why 3.14159265359 diameters in a circumference?


And why is the standard film frame rate 24?

Why did someone come up with 24, rather than a rounder figure like 25? I
could understand 16 or 32, since those can be formed by successively
dividing 1 second by 2.

I realise that persistence of vision governs the *approximate* value -
20-something was found empirically to be the lowest speed at which movement
could be perceived and flicker was not too intrusive.

I wonder if 24 was based on the length of film of a certain frame size (eg
24x18mm for 35mm film) being a whole number of inches (talk about mixing
your units - length of film in feet, width in mm, size of gram in mm).


Wikipedia https://en.wikipedia.org/wiki/Frame_rate says "Many theaters had
shown silent films at 22 to 26 FPS which is why 24 FPS was chosen for
sound." as if it is obvious that from a range of 22-26 fps you'd choose to
standardise on 24 rather than 25. Maybe I'm applying too much numerical OCD
to it, in thinking that if you have a free choice you choose either
multiples of 5 or 10, or else powers of 2. :-)




Record speeds is the obvious progression to this discussion, and I've
found this which you may find interesting. 78.2608RPM anyone?

http://www.aes.org/aeshc/docs/record...ry/speeds.html

And no mention of sixteen and two turds.

Like owning a passport, an American learning a foreign language is a
bit subversive?

Just a thought.


--

Graham.
%Profound_observation%
  #32  
Old March 8th 17, 07:58 PM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 526
Default why 12V?

On 08/03/17 17:09, Roderick Stewart wrote:
I've always assumed 5V was chosen simply because it's easy to produce
from a 6V battery.


No it isn't. If you are talking "dry" cells, the normal design endpoint
voltage is 0.9V per cell, or 3.6v, which is well outside the supply
voltage tolerance for TTL logic, even before the regulator drop.
  #33  
Old March 8th 17, 08:06 PM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 526
Default why 12V?

On 08/03/17 19:52, Graham. wrote:
Surely that would be irrational ;-)


Certainly something to meditate on, transcendentally.
  #34  
Old March 8th 17, 08:28 PM posted to uk.tech.digital-tv
Woody[_5_]
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Posts: 1,761
Default why 12V?


"charles" wrote in message
...
In article ,
Woody wrote:

"Roderick Stewart" wrote in message
...
On Wed, 08 Mar 2017 11:42:21 +0000 (GMT), Jim Lesurf
wrote:

I'm not sure how 5V became the standard for USB power.

TTL logic must figure strongly in the answer.

It's a while since I did electronics. Is 5V (or thereabouts)
based
on
physical properties of the silicon for the transistors in TTL?
I
probably knew this at one time...

I'm trying to recall if RTL or DTL used 5Volts. I did briefly use
some
RTL/DTL as an undergrad.

Yes they did.

But yes, IIUC the old TTL standard devices tended to be quite
fussy
about
the rail voltage.

I've always assumed 5V was chosen simply because it's easy to
produce
from a 6V battery.



Actually probably not. TTL was very pernickety about supply
voltages,


[Snip]
I remember seeing a TTL based unit where the PSU had gone way over
voltage.
All the chips had boiled their encapsulation. It didn't work any
more
either.



It was much more entertaining to cook CMOS despite their much greater
voltage range. The chip would usually blast its way out of the
encapsulation leaving the encapsulation complete bar a hole in the
top!


--
Woody

harrogate3 at ntlworld dot com


  #35  
Old March 8th 17, 09:47 PM posted to uk.tech.digital-tv
Indy Jess John
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Posts: 1,202
Default why 12V?

On 08/03/2017 20:06, Graham. wrote:
On Wed, 8 Mar 2017 11:43:12 -0000, wrote:

wrote in message
...
Why 6.3V for many valve heaters?

And why 3.14159265359 diameters in a circumference?


And why is the standard film frame rate 24?

Why did someone come up with 24, rather than a rounder figure like 25? I
could understand 16 or 32, since those can be formed by successively
dividing 1 second by 2.

I realise that persistence of vision governs the *approximate* value -
20-something was found empirically to be the lowest speed at which movement
could be perceived and flicker was not too intrusive.

I wonder if 24 was based on the length of film of a certain frame size (eg
24x18mm for 35mm film) being a whole number of inches (talk about mixing
your units - length of film in feet, width in mm, size of gram in mm).


Wikipedia https://en.wikipedia.org/wiki/Frame_rate says "Many theaters had
shown silent films at 22 to 26 FPS which is why 24 FPS was chosen for
sound." as if it is obvious that from a range of 22-26 fps you'd choose to
standardise on 24 rather than 25. Maybe I'm applying too much numerical OCD
to it, in thinking that if you have a free choice you choose either
multiples of 5 or 10, or else powers of 2. :-)




Record speeds is the obvious progression to this discussion, and I've
found this which you may find interesting. 78.2608RPM anyone?

http://www.aes.org/aeshc/docs/record...ry/speeds.html

And no mention of sixteen and two turds.


This from Wikipedia:
"The earliest rotation speeds varied widely. Most records made in
19001925 were recorded at 7482 revolutions per minute (rpm). Edison
Disc Records consistently ran at 80 rpm."

Jim
  #36  
Old March 8th 17, 10:03 PM posted to uk.tech.digital-tv
stephen
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Posts: 80
Default why 12V?

On Wed, 8 Mar 2017 16:13:40 -0000, "Brian Gaff"
wrote:

No, I imagine you could feel 48v, something like the line volts of a
telephone.


FWIW 48v DC for telecom equipment is 1 of the few world wide
standards. You can get a belt from it but it is normally treated as
reasonably safe for shock hazards (although welding and sparks are a
different problem).

you missed out the classic electric vehicles - milk floats and stacker
trucks?

In real life telecom battery systems tend to be 4 glorified "deep
discharge" expensive 12v sealed batteries which look pretty similar to
car batteries with attitude......

some of the PoPs at work with older PSTN switches have entire rooms
full of battery strings - with lots of hazard warnings given the
amounts of acid involved, and the risks of hydrogen generation.

huge manufacturing scale will mean common components get re-used where
that makes sense.

to be honest I think you are probably right in the car battery analogy. Its
kind ofstuck like that but not everywhere. I have a tv here where the psu
claimes to be 18v.

Boats operated on double 12 at one time, and many fighting ships use 300hz
AC.
Brian

Stephen Hope
Replace xyz with ntl to reply
  #37  
Old March 9th 17, 09:07 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
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Posts: 4,182
Default why 12V?

In article , Woody
wrote:
The only method of regulating a nominal 6V down to 5V would be a
switching regulator - quite acceptable and easily achieved today but
20+ years ago it was a different kettle of fish. A series pass
regulator needs some headroom - for something like a 7805 about 2.3V
would be needed which is clearly not available, so the only option
would be a zener diode which either has to draw the balance of the
current needed to cause the necessary voltage drop across a resistor,
or provide the control for a series pass transistor.


In principle you could probably engineer a diode or series of a couple of
diodes to drop about 1V and have them in series with the 6V supply. But it
would seem a bit of a daft way to do it when you can simply make a decent
5V supply by other means.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #38  
Old March 9th 17, 05:12 PM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 404
Default why 12V?

On Wed, 08 Mar 2017 22:47:06 +0000, Indy Jess John
wrote:

On 08/03/2017 20:06, Graham. wrote:
On Wed, 8 Mar 2017 11:43:12 -0000, wrote:

wrote in message
...
Why 6.3V for many valve heaters?

And why 3.14159265359 diameters in a circumference?

And why is the standard film frame rate 24?

Why did someone come up with 24, rather than a rounder figure like 25? I
could understand 16 or 32, since those can be formed by successively
dividing 1 second by 2.

I realise that persistence of vision governs the *approximate* value -
20-something was found empirically to be the lowest speed at which movement
could be perceived and flicker was not too intrusive.

I wonder if 24 was based on the length of film of a certain frame size (eg
24x18mm for 35mm film) being a whole number of inches (talk about mixing
your units - length of film in feet, width in mm, size of gram in mm).


Wikipedia https://en.wikipedia.org/wiki/Frame_rate says "Many theaters had
shown silent films at 22 to 26 FPS which is why 24 FPS was chosen for
sound." as if it is obvious that from a range of 22-26 fps you'd choose to
standardise on 24 rather than 25. Maybe I'm applying too much numerical OCD
to it, in thinking that if you have a free choice you choose either
multiples of 5 or 10, or else powers of 2. :-)




Record speeds is the obvious progression to this discussion, and I've
found this which you may find interesting. 78.2608RPM anyone?

http://www.aes.org/aeshc/docs/record...ry/speeds.html

And no mention of sixteen and two turds.


This from Wikipedia:
"The earliest rotation speeds varied widely. Most records made in
19001925 were recorded at 7482 revolutions per minute (rpm). Edison
Disc Records consistently ran at 80 rpm."

Jim


I've got a Caruso 78 that is actually marked 80RPM



--

Graham.
%Profound_observation%
  #39  
Old March 9th 17, 06:37 PM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 1,187
Default why 12V?

"Graham." wrote in message
...
I've got a Caruso 78 that is actually marked 80RPM


I've got a shellac-on-aluminium disc made by the BBC of a talk that my
grandpa made on Children's Hour some time in the 1950s. It's nominally 78
rpm, but must have been recorded at a slightly slower speed because
grandpa's voice sounds slightly too high-pitched (*). He is also using a
standard BBC announcer's accent instead of his own educated West Riding
accent, which has some *very* odd vowels. I think he must have overdone the
RP accent, so you got phrases such as "like a ballett fram a gan" (like a
bullet from a gun). I teased him mercilessly about it when he first played
it to me. He said that he deliberately over-emphasised the RP accent as a
protest when he was told that his own accent was not acceptable on national
radio, and accidentally-on-purpose let slip the odd northern vowel to make
it clear where he came from and that it was all a charade.


(*) One way to tell would be to look for the nominal 50 Hz mains hum in the
spectrum and correct the speed until the hum was exactly 50 Hz.

  #40  
Old March 9th 17, 08:16 PM posted to uk.tech.digital-tv
Vir Campestris
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Posts: 392
Default why 12V?

On 08/03/2017 12:44, The Other John wrote:
On Wed, 08 Mar 2017 11:43:12 +0000, NY wrote:

And why is the standard film frame rate 24?


Was it set by the Merkins? If so could it be because of their 60Hz
mains? You would get 5 positive and negative mains peaks per frame if my
sums are right, thus avoiding strobing effects.

Merkin TV is of course (almost exactly) 30Hz.

Andy
 




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