[time-nuts] Simulation

Magnus Danielson magnus at rubidium.dyndns.org
Sat Aug 14 16:55:30 UTC 2010

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...


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