On 08/14/2010 06:39 PM, Javier Herrero wrote:
Hello,
I've read at least two similar stories in "Troubleshooting Analog
Circuits" by Bob Pease.
One is that it seems that some time ago, National Semiconductor started
shipping LF411s marked as LF351s as an "improvement"... and as Bob says,
most of the customers probably were happy with that (I think that most
of them probably never noticed the change), but the gain on the trim
circuit was reversed (in the LF351, if you turn the trim pot in one way,
Vos increases - in the LF411, turning it in the same way makes Vos to
decrease), and this probably would have made some people not so happy
with the improvement :)
Another story is about 2N3771 transistor, initially a single-diffussed
part, but later an epitaxial base part - with a lot more gain bandwidth
product. But since the 'new' 2N3771 meets and exceeds original 2N3771
specs, the same part number was used - but the part is quite different
(and published specs continues being the JEDEC ones). So you can imagine
that in some applications it would be quite a lot of difference if you
breadboard with the older, and during the manufacturing phase you
(probably without knowing it) switch to the new part.
One side-effect is that you run into possibilities of oscillation. This
have happend and was the cause of a GPS outage in a US Harbour a few
years back. What was a wise design became an enemy due to a subtle
change in part. Don't recall if the part was replaced by an "equivalent"
or same part-number, but the new version didn't work as expected during
all conditions...
Cheers,
Magnus
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
