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Old 4th June 2012, 09:11 PM   #23661
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Quote:
Originally Posted by Wavebourn View Post
I remember a story, on radio plant in Riga, Lituania, they got a party of receivers that did not work at all. Investigation revealed that a lady in warehouse who worked there many years tried what she believed to correct an error: new capacitors were of different color, she thought it is wrong, so she replaced them by other capacitors from different bin.

She knew nothing about picofarads...
It is high probability that is just an urban legend, or an anecdote simply because during soviet times manufacturing quality/process management was low to non existent, so people used to hyperbolise or make jokes about it.

A bit of OT here. Riga is capital of Latvia. Lithuania's capital is Vilnius.
I don't know why but it is very common mistake.
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Old 4th June 2012, 09:14 PM   #23662
bcarso is offline bcarso  United States
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Quote:
Originally Posted by Wavebourn View Post
I remember a story, on radio plant in Riga, Lituania, they got a party of receivers that did not work at all. Investigation revealed that a lady in warehouse who worked there many years tried what she believed to correct an error: new capacitors were of different color, she thought it is wrong, so she replaced them by other capacitors from different bin.

She knew nothing about picofarads...
One engineer who worked for my father was red-green colorblind. Not at all good for resistor color codes.

Later, to help get the right transistors manually inserted, the incoming PNPs got painted on the top of the TO92 case with red nail polish. When I designed something with JFETs (very much unappreciated by production) they got painted white or blue depending on the part.
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Old 4th June 2012, 09:39 PM   #23663
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Black is sooo passé.
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Old 4th June 2012, 09:44 PM   #23664
bcarso is offline bcarso  United States
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Originally Posted by jacco vermeulen View Post
Black is sooo passé.
Would that it were for consumer audio electronics, whose control markings become progressively less legible as our vision deteriorates with age. I think it was Adcom who once experimented with white chassis and dark markings, but evidently it had a low spousal acceptance factor, or lacked appeal in some other way.
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Old 4th June 2012, 09:46 PM   #23665
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Originally Posted by jneutron View Post
We are in agreement here..loop area is controlled by where the current centroid lies.
Jneutron and JCX thanks for this interesting exchange of thoughts. If you could please explain what is the current centroid and how it is related to loop area, I could learn even more,

Vac
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Old 4th June 2012, 09:54 PM   #23666
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Originally Posted by bcarso View Post
who once experimented with white chassis and dark markings.
Braun Atelier series, early 1980s.
All-White, from the turntable all the way to the loudspeakers.

(horrible)
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Old 4th June 2012, 10:09 PM   #23667
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Originally Posted by jacco vermeulen View Post
Braun Atelier series, early 1980s.
All-White, from the turntable all the way to the loudspeakers.
(horrible)
And therefore collectible
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Old 4th June 2012, 10:27 PM   #23668
gpapag is online now gpapag  Greece
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Originally Posted by scott wurcer View Post
Yes, we do a 3D extraction of bonds and package for giga-Hz IC's...
Scott
Thank you for the inside look.
If I would ask for your opinion as to why it is not performed on lower freq. Ics too? (Multiple choise question)
a. Negligible effects at these freq.
b. Effects are not that dramatic at these freq.
c. Effects are equally important but layout correction not feasible within IC size, due to large dimentions –length, height- required for lower freq.
d. None of the above. (Please elaborate in 20 words)


JC, KBK, jneutron, bcarso, simon, jcx, thanks for responding.

George
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Old 5th June 2012, 01:28 PM   #23669
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Originally Posted by vacuphile View Post
Jneutron and JCX thanks for this interesting exchange of thoughts. If you could please explain what is the current centroid and how it is related to loop area, I could learn even more,

Vac
This is probably best setup as a wiki...

The current centroid is the average center of the current. Think of a frisbee balancing on a finger. If you have the (mass) centroid of the frisbee directly above your finger, the frisbee is balanced. If the frisbee is off center, it will tip. If you glue a quarter on the edge, you have changed where the centroid is, and it will have a different balance point which you can find by trial and error.

Now think of the current in a uniform conductive cylindrical wire (with the return path for this current at infinity so there are no proximity effects). At DC, the current will flow equally through the entire cross section of the wire. The current centroid will be exactly in the center of the wire. As you increase the frequency of the current, the current will begin to skin (go to the outside of the wire as a result of the lenz effect (law). The current centroid will remain exactly in the center of the wire.

A braid is exactly this...a cylindrical conductor where the current is confined to the outer "surface" of the wire, in this case the outer surface being the wire. Any current flowing in this braid (again, no proximity) will flow uniformly, and the current centroid is exactly in the geometric center of the braid.

A coax puts a wire in the exact same location as the braid's centroid. For this case, both the central core wire and the braid have centroids which are on the exact same line in space, coaxial... So we say this structure has a common centroid.

If the current is flowing equal and opposite for the core and braid, the magnetic fields external to the structure will cancel. This applies to all structures which have a common centroid.

Loop area is defined as the area which exists between the centroids of the "send" wire and the "return" wire. This loop area is what will trap time varying magnetic flux and as a result, a voltage can be induced between the conductors. A coax has no loop area.

What jcx and I have touched on, is the fact that the loop area can be current dependent. A simple example would be a pc board with a long trace that starts and ends with a source and load rca jack an inch apart on the board, with the "hot" trace on the top surface of the board travelling the entire length and back on the top surface, with the current return via a ground plane. At DC, the "hot" current will flow via the entire top trace from the source jack to the load jack, and the current will return via the shortest resistive path, a straight line jack to jack within the ground plane.

Inductively, this loop has the largest area at DC because the send or hot current goes the entire top trace, and the return current takes a much different path, direct. Because current always takes the path of lowest impedance, at DC the ground return will be resistance dominated. As the frequency increases, the inductance along the straight line starts to come into play, and the path of least reactance within the ground plane starts to migrate towards the top trace. The ground current is attempting to bring it's current centroid as close to the centroid of the hot current. If you measure this system's inductance, you will find it is very high at low frequency, and drops as frequency rises.

In the limit, this setup will act like a stripline, high frequency currents will ignore the entire ground plane and travel directly under the top trace.

With wires and coils and electromagnetics, this effect is referred to as the proximity effect. The biggest problem with coils can be seen in the previous example...at dc, the resistance of the ground plane is very small because it's a honkin conductor. But at high frequency, only a very small portion of the copper is actually conducting, most of it does nothing anymore. In coils, this means that the effective resistance is much higher than the dc resistance of the wire.

This will also occur in a chassis.

The important thing to realize is that as the frequency goes up, the current centroids will attempt to get closer to each other lowering the system inductance. Many physical equipment designs do not worry about this effect. I believe JC et al has been successful because they do not ignore it. Perhaps not fully understand it, but use their ears in liu of maxwells equations in entirety.

My apologies for the length...I'll stop here, it's too long already.

j
ps.. going to have to stop editing for clarity, my 15 minutes is gonna run out.

Last edited by jneutron; 5th June 2012 at 01:42 PM.
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Old 5th June 2012, 01:48 PM   #23670
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Quote:
Originally Posted by jneutron View Post
This is probably best setup as a wiki...

Because current always takes the path of lowest impedance, at DC the ground return will be resistance dominated.

j
ps.. going to have to stop editing for clarity, my 15 minutes is gonna run out.
Gee now I can quote you out of context as saying when you parallel resistors only the lowest value counts!

Very nice piece!

ES
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