[sdiy] marked/selected components

[John Luciani]

The devices that are daubed with paint dots most likely were screened by the
OEM not the device manufacturer. If the device manufacturer goes through
the effort of screening devices they usually append a suffix to the
part number and
charge you more money.

It may be difficult to quantify the differences between "red dot",
"blue dot", etc.
There was probably a screening proceedure with instructions to "mark the parts
in tube 1 with a red dot, tube 2 with a blue dot" etc. Without the
test proceedure
(or test program) you won't be able to associate the dot color with an
electrical
specification.

Since the  LM324 is a cheap opamp with a high offset voltage (apx 5mV) it
was probably screened for offset voltage (especially if was used in test
equipment).

(* jcl *)

On 4/29/06, anthony <aankrom at bluemarble.net> wrote:
> I have seen in certain schematics where it specifies that a certain part is
> "selected" - notably CA3080's and MN3005's, and also transistors of course.
> One schematic for a filter specified selected transistors for an expo
> conveter: "red" for 2N3904 and "blue" for 2N3906. Now in the context of
> transitors, these color designations are familiar and make sense to me
> because many transistors, Japanese ones especially designate hfe by color or
> letter code (the letter code usually being an abbrev. for a color name...).
>
> My question is: what do the colors mean for other components? I have seen
> CA3080's specified as "selected: red". I have some CA3080E's that came from
> some stereo audio gear that are daubed with red paint dots. Are these
> "choice" in some way? I also have some LM324's that came from some test gear
> that are daubed with white paint. And in addition I also have several sets
> of 2SA733's and 2SC945's that came from the same pieces of gear (I think all
> driving VFD displays) that are daubed with either silver paint or white
> paint. My guess is that these transistors were matched in some way, but is
> that necessary for a VFD? My biggest question is for the red-dot CA3080's
> and the white-daubed LM324's though.
>
>
>
>


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