PET composite video adapter

Tony Duell ard at p850ug1.demon.co.uk
Tue Oct 14 13:07:11 CDT 2008


> > > The schematic shows the horizontal sync coupled to a gate via a "2200 mf"
> > > non-polarized cap.  I don't know that I have any disc or ceramic caps that
> > 
> > IO think we can instantly eliminat 'mf' == millifarad (which is what it 
> > should be!), since that's then 2.2F, which is rediculously large
> 
> Of course.  I never thought it was millifarad.

Well, it's what it _should_ be. Mind you, millifarad is not a 
commonly-used unit for some unknown reason (I routinely see capacitors 
marked 100000uF rather than 100mF or even 0.1F), although i have seen it 
used in, I think, an HP manual

Incidentally, I saw a 2.7kF (no, not a typo!) low-voltage electrolytic in 
a catalogue recently. And to think that when I was at school the physics 
'teacher' told us that a 1F capacitor would be 'larger than this room' 
and that we'd never seen on. About a week later I dropped a square plasic 
object on his deck -- a 1F capacitor that I'd bought from Farnell or 
somewhere.

> > 2200nF (==2.2uF) would be possible, but it's a very odd way to write it. 
> 
> Yes.  This was also written in the 1970s, so I'm trying historical
> interpretation as well as what's obviously written.

nF was common in Europe in the 70's, much less common in the States, I think.

>  
> > 2200pF (==2.2nF) is quite possible, for some reason some people 
> > (particularly in the States) don't like the unit 'nF'. That would also 
> > seem to be a suitable value for coupling a 15kHz signal. 
> 
> 2200pF does sound reasonable.  I am one of those who never grew up
> using nF, so I don't tend to use it (I learned milli-microfarad from
> my father for pF, he, in turn, was a Ham in the 1950s).

Err, millimicrofarad = nanofarad. The picofarad is the micromicrofarad. 
I've seen  uuF (where the 'u' is actually $\mu$) in old manuals.

Am I the only person to remember the millimicron as an equivalent for nm 
when talking about optical wavelengths, etc?

-tony




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