Nixies, was Re: Octal

[Roy J. Tellason]

On Monday 04 September 2006 07:12 pm, Tony Duell wrote:
> > > I would seriously recomend against rectifying the mains for something
> > > like this. Non-isolated PSUs have the nasty habit of making things live
> > > that you least expect, and may kill you (or worse, damage a classic
> > > computer).
> >
> > Oh,  I wasn't suggesting that,  simply pointing out that once you got
> > your isolation a simple rectifier would do the trick just fine...
>
> Depends on the turns ratio of the transformers...
>
> > I've had my experiences with non-isolated equipment,  more than I ever
> > wanted, and don't plan to build any to add to that.  :-)
>
> Me too. I grew up fixing series-string radios and TVs (until the coming
> of 'baseband' audio and video sockets, such as the SCART connector, most
> TVs sold in the UK, even semiconductor-based ones, had a live chassis). I
> don't much care for working on such units.

I've worked on my share of that stuff as well,  and I don't care for it 
either.

> What amazes me is that in the 1950s and 1960s, UK magazines published
> several educational courses. Typically you'd start by building a crystal
> set, then turn it into a 1-valver (leaky grid detector), then add audio
> stages, RF stages, and maybe end up with a superhet.
>
> Thing is, you got the HT (B+) by half-wave rectifying the mains. The
> exposed metal chasis was connected to mains neutral. And you had
> headphones. You know, that could easily turn into an electric chair...

I'm not familiar with mains wiring there,  is the connection in any way 
polarized?  Lately I've been running into those stupid polarized plugs here,  
but there are still numerous extension cords and outlets that don't have the 
wider slot and there's no guarantee of them being wired properly anyway, so I 
usually end up having to fix those with a nibbling tool for them to be usable 
at all.  I don't understand why they didn't start out with a polarized setup 
in the first place,  if one wire was supposed to be grounded.

> > > If you use back-to-back transformers as I've suggsted, the actual
> > > voltage got get out depends on the turns rations, of course. Maybe a
> > > simple rectifier will be enough, maybe you need a doubler.
> >
> > Many suggestions that I've seen illustrated like that suggest using two
> > identical transformers,   which should get you the same thing out as you
> > put in.
>
> YEs, but there's no _requirement_ to do that.

True.

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