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Today's topics:

* OT: Is this question too challenging for a BSEE graduate? - 3 messages, 2
authors
http://groups.google.com/group/sci.electronics.repair/t/31ba2b6a402a3720?hl=en
* Discount Nike Air Jordan 7 Shoes Catalog (http:// www.cntrade09.com) - 1
messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/13684833d3f00ae4?hl=en
* Another reason to hate CFLs ... - 3 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/87ea27a2579f0316?hl=en
* Panasonic Plasmas/LCDs of Past 5 years - "Volume Leveler" Function - 1
messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/192fcec79e92313a?hl=en

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TOPIC: OT: Is this question too challenging for a BSEE graduate?
http://groups.google.com/group/sci.electronics.repair/t/31ba2b6a402a3720?hl=en
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== 1 of 3 ==
Date: Sun, Oct 24 2010 11:04 pm
From: isw

In article <ia141b$kad$1@news.eternal-september.org>,
"William Sommerwerck" <grizzledgeezer@comcast.net> wrote:

> >> The principle is this... In a stable op-amp circuit, the
> >> feedback forces the inverting and non-inverting inputs
> >> /to have the same voltage/. The rest is trivial arithmetic.
>
> > That statement is so significant, and so rarely understood...
>
> Indeed. National Semiconductor used to have an on-line course in op-amp
> circuit design, and this principle -- which should be the very first words
> out of the instructor's mouth -- is nowhere stated. Shame on you, Bob, shame
> on you.
>
> In case the reason isn't obvious -- an ideal op-amp has infinite gain. If
> there were /any/ voltage difference between the inverting and non-inverting
> inputs, the op-amp's output would slam up against the positive or negative
> rail.
>
> In practice, an op-amp has finite gain (usually between 100K and 1000K).
> This means the actual voltage difference has to be something other than
> zero. But it's is still so close to zero that it can be ignored for the
> purposes of analysis.
>
> By the way, I cut my op-amp teeth nearly 40 years ago on the wonderful
> Philbrick brook. One of the greatest pieces of technical writing ever (I
> keep a copy for inspiration), and still a classic.

Sounds like you predate me -- but not by much. I cut my "op-amp teeth"
on the earliest National Tech Notes (when they had that wonderful "NS"
logo where both glyphs were identical, with one rotated and flipped).

Isaac

== 2 of 3 ==
Date: Mon, Oct 25 2010 12:43 am
From: "William Sommerwerck"

>> It is pretty easy if you know about how the op-amp
>> will do whatever it can to make the voltage at pin 2
>> the same as pin 1.

> But is this really true? This sounds like it might be either
> a gross oversimplification or a possible falsehood.

No, it's fact. It is, as I said, /the/ fundamental principle of op-amp
circuit design.

I can't think of a book that discusses this in a fairly simple way. Even the
Philbrick book -- which is hard to find these days -- doesn't address the
matter as directly as I'd like. But, trust me. Most op-amp circuits can be
analyzed by assuming the voltage is the same, then applying simple circuit
analysis. You might start with the basic op-amp inverting amplifier, and see
what happens.

== 3 of 3 ==
Date: Mon, Oct 25 2010 12:46 am
From: "William Sommerwerck"

>> By the way, I cut my op-amp teeth nearly 40 years ago of
>> the wonderful Philbrick brook. One of the greatest pieces
>> of technical writing ever (I keep a copy for inspiration),
>> and still a classic.

> Sounds like you predate me -- but not by much. I cut my
> "op-amp teeth" on the earliest National Tech Notes (when
> they had that wonderful "NS" logo where both glyphs were
> identical, with one rotated and flipped).

Probably written by Bob Widlar. Unfortunately, NS is still using his
documents, which are now rather dated. Nothing wrong with continued respect
for his genius, but /someone/ needs to update them.

==============================================================================
TOPIC: Discount Nike Air Jordan 7 Shoes Catalog (http:// www.cntrade09.com)
http://groups.google.com/group/sci.electronics.repair/t/13684833d3f00ae4?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Oct 24 2010 11:18 pm
From: cntrade08

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==============================================================================
TOPIC: Another reason to hate CFLs ...
http://groups.google.com/group/sci.electronics.repair/t/87ea27a2579f0316?hl=en
==============================================================================

== 1 of 3 ==
Date: Sun, Oct 24 2010 11:24 pm
From: "Geoffrey S. Mendelson"

Jeff Liebermann wrote:
> Drivel: I was defrosting the fridge with a screwdriver and hammer,
> when I managed to puncture the cooling coils, releasing the gas. I
> hate days like this.

My first wife did that circa 1974. You can patch the coils and refill them,
HOWEVER what I did not learn until a few years ago is that you have to
to empty the coils with a vacuum pump before you add new refrigerant.

Adding new refigerant to a system with air in it does not work very well.

You also may want to not mention this to anyone, don't you need a permit
to release refrigerant into the air in California?

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
To help restaurants, as part of the "stimulus package", everyone must order
dessert. As part of the socialized health plan, you are forbidden to eat it. :-)

== 2 of 3 ==
Date: Mon, Oct 25 2010 12:32 am
From: "William Sommerwerck"

> I wonder whether colour blindness has anything to do with this, and the
> reason why some of us seem to have a problem with the colour rendition of
> CFLs, whilst others don't ? Long ago when I was in senior school, I was
> tested for colour blindness, and was declared red blind and green
> insensitive (I think) which I understood to mean that I couldn't pick out
> certain shades of green amongst other colours, and couldn't see some
shades
> of red at all. In normal everyday life, this has never caused me any
> problem, and as far as I am concerned, I see and distinguish colour as
well
> as the next guy, (although maybe differently in perception) but that is
> assuming the natural condition of daylight, which all of the 'traditional'
> light sources, including linear flourescents, mimic reasonably well, at
> least at the lower end, and in terms of the spectra being reasonably
'bulky'
> and continuous. However, that is not the case for the typical CFL
spectrum,
> which is *extremely* discontinuous. Could it be that the zero emission
dips
> in the spectrum, correspond wholly or in part, to spectrum sensitivity
> deficiencies in my eyes, causing my colour blindness to become significant
> under that light, and leading to some colours all but disappearing to me.
> That would certainly account for why some blend colours like orange or
> violet on the resistor colour bands that started all this, become
> indistinguishable (to me) from the single colour components which make
them
> up.

Color vision is usually tested by seeing whether people can /distinguish/
colors, rather than identify them. Human males sometimes suffer from
red/green "color blindness" -- difficulty in distinguishing them. My father
had that problem; fortunately I didn't inherit it.

Peter Wensberg, a vice-president at Polaroid, reported that Dr Land ran the
entire book of color-perception charts past him, and said he was the first
person he'd met who failed every one. Whether this meant Mr Wensberg could
not see color at all, I don't know. But he couldn't /distinguish/ them very
well.

A co-worker once asked me to help with selecting colors for a page he was
designing. It turned out he had red-green problems. I showed him a
fluorescent-green pen. "What color does that look like to you?" "Orange". I
don't know what "orange" looked like to him, but he couldn't distinguish
that green from orange.

It isn't clear how the lack of red in fluorescent lamps would interact with
red/green blindness.

For what it's worth, conventional "linear" fluorescents, regardless of their
color balance, have never looked "right" to me. The better CFLs are the
first fluorescents that look fairly natural.

== 3 of 3 ==
Date: Mon, Oct 25 2010 12:45 am
From: "N_Cook"

Arfa Daily <arfa.daily@ntlworld.com> wrote in message
news:tn5xo.73935$J84.37331@newsfe27.ams2...
>
>
> "LSMFT" <boleyn7@aol.com> wrote in message
> news:%O2xo.761$kS.755@newsfe17.iad...
> > Arfa Daily wrote:
> >> As if any more reasons were needed on top of their horrible startup
> >> characteristics, their ugliness, their sick coloured light, and their
> >> inability to last for a fraction of the claimed lifetime :-(
> >>
> >> Like most of us, I suspect, I have hundreds of component drawers, which
> >> over the years have become mixed up and confused, so in the
> >> circumstances of work being very quiet at the moment, I decided to have
> >> a major tidy up and clear out of redundant components. As a first move,
> >> I decided to rationalise the resistors, and re-store them by individual
> >> value, rather than in groups of values in the same drawer.
> >>
> >> Now the other day, the bulb in my Anglepoise bench light failed, and as
> >> it was the last 60 watt pearl one I had - nowhere stocking such an
> >> animal any more due to EU ecobollox intervention - I put in a CFL that
> >> had come free in a cornflake packet or some such nonsense. Once it has
> >> warmed up in the morning - at least one coffee drinking time needed for
> >> this - it seemed to work reasonably well. Until, that is, I started
> >> trying to identify the resistors in my old drawers to move them into
the
> >> individual value drawers in the new location.
> >>
> >> The spectrum from this lamp is so poor and discontinuous, that it is
> >> almost impossible to resolve red from brown from orange, or violet from
> >> blue or grey. Absolutely bloody useless. If I can't find any more 60
> >> watt pearl bulbs on the 'net, then I'm going to modify the lampholder
to
> >> take a low voltage halogen downlighter bulb, and hook it to a 12v
> >> transformer.
> >>
> >> Arfa
> >
> > People like you have real issues. I have had 100% CFL's in my home for
> > decades. Guess what, they are better than candles.
> > I will be switching to LED's when they are available for all around use.
> >
> > --
> > LSMFT
>
> Maybe I do have issues - see my post in this thread about colour
blindness.
> But setting that aside, I am sick of people telling me that I can't
actually
> see what I clearly can, because *they* can't see it, and are happy to be
led
> by the nose down the route of this substitute technology in the name of
> green mist brigade ecobollox.
>
> And you know what else ? You're right ! CFLs are better than candles. But
> compared to incandescent lamps, they suck big time. So if that's the sum
> total of your contribution, and you are happy with the shitstreet pieces
of
> crap, that's just fine.
>
> I, and thousands of others, are not.
>
> Arfa
>

A few stripes of red permanent-ink felt-tip pen over the CFL tubes "warms"
up the colour lovely - what's all the fuss about ?

==============================================================================
TOPIC: Panasonic Plasmas/LCDs of Past 5 years - "Volume Leveler" Function
http://groups.google.com/group/sci.electronics.repair/t/192fcec79e92313a?hl=en
==============================================================================

== 1 of 1 ==
Date: Mon, Oct 25 2010 12:48 am
From: "William Sommerwerck"

It's remotely possible there is no way to adjust it.

I'd suggest pouring a glass of your favorite beverage, then working
carefully through the set's menus. If there is an adjustment, you /will/
find it. You might have to look very closely, though.

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