[sdiy] Curious capacitor in Music Easel ring modulator

[Roy J. Tellason]

On Tuesday 26 August 2008 04:57, ChristianH wrote:
> My guess ist that in 1973 it wasn't practical to use a non polarized
> 4.7 u cap - wasn't it that about anything beyound 1 uF was electrolytic
> back then?
>
> Christian

I worked on some industrial stuff in 1975 that used "tubular" caps (of some 
sort,  I'm not real sure what kind they were),  largish,  more rectangular 
than actually tubular,  and in values around that point,  say down to around 
100nF and maybe up to as much as 4.7uF,  most definitely non-polarized.  
These were all used in timing circuits like half monostables,  so there 
wasn't a need for a nonpolarized cap there,  but my guess is that they wanted 
a bit more precition in terms of values than you'd get from an electrolytic.

Hope that helps with the availability question anyhow.

What I'm very curious about is that in scrapping certain vintages of VCR I'm 
finding electrolytics all the way down to 100nF,  while there are also 
polystyrene and ceramics in that value in there as well.  Not just that value 
either,  but 220nF,  330nF,  470nF,  etc.  I'm not real clear as to why 
they'd use one of those as opposed to the other types,  maybe a cost issue?

> On Mon, 25 Aug 2008 22:10:02 -0400 Aaron Lanterman
>
> <lanterma at ece.gatech.edu> wrote:
> > Totally hypothetically speaking, suppose one was breadboarding the
> > "balanced modulator" shown here:
> >
> > http://rubidium.dyndns.org/~magnus/synths/companies/buchla/Buchla_2080_5_
> >200.jpg
> >
> > Should I - I mean, the hypothetical "one" - really put in C1, which is
> > a 4.7 muF electrolytic cap? I see no particular reason to believe the
> > voltage on one side of it would be consistently higher than the
> > voltage on the other, which gives me pause and makes me wonder about
> > it in the original circuit. (I've seen electrolytic caps like that in
> > other Buchla stuff, where it looks like it's meant as a DC block, but
> > I can't see any reason to assume one side would be higher voltage than
> > another which feels dubious given that it's an electrolytic. I have
> > heard that electrolytics can take a bit of AC action as long as the DC
> > isn't going the wrong way, but that feels dubious too.)
> >
> > - Aaron
>
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