[GreenKeys] History - Why voltages and frequencies are chosen(5v & 3.3v l...

[Christian Gauger-Cosgrove]

The larger DEC minicomputers (the PDP-15 family, the "large" PDP-11
family members (like the 11/70), the PDP-9 if I remember correctly;
the PDP-10 doesn't count since it's a verdammt mainframe), and I
believe most of IBM's earlier midrange systems -- like the System/3 --
used 208V three phase wye.


At least in North America. I don't really recall what the manual said
they ran on in Europe.


Cheers,
Christian




On 22 November 2012 21:37,  <WA5CAB at cs.com> wrote:
> I don't recall ever checking on why 5V or 3.3 V were used for logic but
> always assumed it was at least in part because of inherent voltage ratings
> of the components and/or was enough lower than 6.3 VDC to allow a regulator
> to operate properly.
>
> And the 50/60 cps subject has been beaten enough today so I won't add any
> comment.
>
> 6.3V (and 12.6 V and 25.2V) for tube filaments is a result of the
> characteristics of the lead-acid cell and the fact that early automotive
> systems were nominally 6 VDC (then 12, then 24) (with engine off of course).
> The fully charged voltage of a lead-acid cell (after removal of the surface
> charge by a slight discharge) is 2.1 VDC.  Three cells in series yields 6.3
> VDC and the heavy use in automotive applications made the batteries readily
> available for battery operated radios (farm sets, and the like).  As the AC
> operated sets had no particular technical reason (consumer stuff, anyway) to
> prefer a different voltage, 6.3 volt filaments became common.
>
> On the 120/220 VAC question, there never has been a system with those
> nominal voltages, whether single or 3-phase.  The standards over the years
> have been 110/220, 115/230, 117/234 and 120/240 for single phase.  Because
> the standard single phase pole pig has a center-tapped secondary and you
> can't get 220 volts line to line if the line to CT is 120.  The most common
> (probably) low voltage 3-phase system is currently 120/208 wye.
>
> In a message dated 11/22/2012 18:18:10 PM Central Standard Time,
> 1oldlens1 at ix.netcom.com writes:
>
>
> ----- Original Message -----
> From: "Keith Lueck" <kwlueck at swbell.net>
> To: <notbago at yahoogroups.com>;
> <i3detroit-public at googlegroups.com>; <acti at provide.net>
> Cc: <Greenkeys at mailman.qth.net>
> Sent: Wednesday, November 21, 2012 12:57 PM
> Subject: Re: [GreenKeys] History - Why voltages and
> frequencies are chosen(5v &3.3v logic, 6.3v filaments,
> 120/220 VAC, 50/60Hz etc)
>
>
>
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
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