On Fri, 21 Aug 2009 14:48:23 -0400, jeff_wisnia
wrote:
Jon Elson wrote:

I remember renting a student apartment in Boston circa 1955 and
finding out to my horror that the place was still on DC.

I was a "Hi-Fi" buff at the time and couldn't put up without AC to run
all my gear, and I didn't want to try and get by with the vibrator DC
to AC inverters available back then.

So, I moved out the day after I moved in, and the landlord was nice
about it.

My God, what COULD you run off DC back then?

Light bulbs fer sure. G

Anything that was a straight resistive load works on DC - toasters,
hot-plates, coffeepots.

Now if the hotplate has a thermostat and that switch wasn't rated to
break DC, you could have some excitement...

Let's see, most vacuum cleaners had universal motors and would
probably run on DC.

Universal Motors with brushes, yes. Early vacuum cleaners, early
table fans, early mixers and blenders.

Induction, synchronous, and shaded-pole motors, no. Most clocks have
a synchronous motor, AC only. Even the Simplex Master Clock systems
are out, they had the hourly sync pulse but the indivdual clocks still
run on synchronous motors.

Now they could use a Self-Winding style clock that has a universal
motor to wind a spring for a mechanical escapement movement, but that
would tend to be inaccurate. And those movements made noise when they
rewound every so often, which would be as loud as heck in a silent
room at 3 AM.

I guess smaller TVs and table radios would
run on DC, but that might be about it!

Many small radios back then were referred to by the cognizanti as "AC/DC
Sets". They had no power transformers in them and they used tubes with
various filament voltages like 12, 35 and 50. The typical 5 tube set
would run all the tube filaments in series from 120 volts (AC or DC, it
didn't matter which.) I can't recall whether the line cord was polarity
sensitive and had to be plugged in the "right way" to get electrons to
flow through the rectifier tube (usually a 35Z5 ?). Perhaps some antique
radio buff will check in here on that.

That's the classic "5-Tube AC/DC Superhet (-rodyne) Radio" design.
I owned several through the years. You can Google up more
information using that term than you can handle - they even had AGC on
the incoming signal.

The trick to putting all the filaments in series is they all needed a
common filament /current/ so they all worked in series. And the other
trick was not needing more than 120V B+ plate voltage, so they didn't
need a high voltage section that requires a vibrator or dynamotor for
DC. They developed a set of tubes specifically for the usage.

But, I don't recall ever seeing a TV which would work off DC line voltage.

Not without a vibrator or a dyanmotor (or a power-transistor driven
Inverter or DC-DC Converter in new gear) you wouldn't - you need a few
thousand volts of B+ to get the electron stram to go from the gun
through the picture tube to light the phosphors...

And AFAIK all the old sets have used the line frerquency as a
reference to get the Vertical and Horizontal Hold cues from. They
added the Colorburst crystal to get the timing for color TV, but the
utility AC frequency still gave a nice stable sync reference.

-- Bruce --