[sdiy] Resistor types

[Roy J. Tellason]

On Saturday 11 September 2004 02:06 am, harrybissell wrote:

>With little exception today, there is no reason to specify a carbon comp 
> except for
>
> 1) pulse power rating - carbon comp can really, REALLY suck up an overload.
> Like if you have a 1/2 watt power dissipation that consists of a low duty
> cycle 5 amp pulse !!! Carbon COMP can do it - metal and carbon film cannot. 

Interesting to know,  dunno if I'd have thought of it.  :-)

> 2) RF.  Low inductance (nuff said).  I had one circuit that failed with a
> metal film (not a synth btw...) because metal film (with in this case, a
> spiral wound element) got hot from RF induction heating
> and blew out. Carbon Comp would survive this easily.

And I wonder how often (if at all) the designers of circuits using _digital_ 
stuff even consider this.  One would not expect those folks to have much 
experience with RF...

<...>

> unless you are one of those lazy engineers who puts the pot from rail to
> rail... and figures the right value is in there somewhere  (he blushes and
> looks at the floor  :^)

:-)

<...>

> Seriouly.. Peter has a good point. There are two solutions
>
> 1) Bright light and a good magnifier. A neat little Bausch and Lomb "10x
> Coddington" costs $10 or so... and you can hold it siz inches from the board
> (really good depth of field).

I had to break down and buy one of those lighted magnifiers a few years back.

> Good light is essential... I use a combo of incandescent and fluorescent to
> get goos color rendition...

Indeed.  During a recent session of sorting salvaged parts I was bothered a 
bunch by the "color ambiguity" here on my desk,  with only incandescent 
lighting.  I used to have only flourescent lighting over my bench,  and don't 
have that option just now.

> ...and I squint a lot :^P

It sucks,  not being able to see as well as I used to!

<...>

> 3) Vector T42-1 terminal... wires go on the bottom, component on the top.

Which one is the T42-1?  The number sounds familiar,  but I have no idea where 
my vector catalog is. 

<...>

> > On the other side of the very side coin:  I  remember once not so long
> > ago, someone on AH (i think), in an attempt to preach  the
> > fantasmagorialness of a (name withheld, but it's a brand of modular)
> > bragged about it's abundant use of trim pots, sighting that has an
> > obvious marker of it's design superiority.

> Hmmm.  A rev 2 prophet had 120 trim pots. The rev 3 had 60.  I re-did mine
> and added another twenty to calibrate the poly mod section. More thrim pots
> is bad... so are too few. The right number is "All the ones you need, are
> there"

This reminds me of a job interview I went on a number of years ago.  I don't 
even remember what the product was,  only that it was a hybrid of both analog 
and digital technology,  and on a couple of fairly large (square foot or so?) 
boards.  The digital stuff was more or less like any other digital stuff but 
the analog board was chock full of both large numbers of 1% resistors and 
trimpots all over the place.  Part of my job would have been to set these 
boards up, and adjust all of those trimpots...