Nixies, was Re: Octal

[Tony Duell]

> > 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,  

Most UK mains sockets (even at that time) would be the 3 pin 13A 
rectangular-pin ones. There is no 2-pin plug that fits these, they are 
polarised.

But in the 1950s it would not be that uncommon to find 2 pin mains 
sockets. No earth, and not polariesed. These came in 2A, 5A, and 15A 
versions IIRC. There were also 3 pin versions [1] but in  wonderful piece 
of design, the pin spacing was diferent -- 2 pin plugs do not properly 
fit the 3 pin sockets.

[1] The spec mentions a 30A version. I have never seen one, I have never 
met anyone who's seen one. A friend who works in the electricity supply 
industry can make the same claim. 

However, it is a very Bad Thing to assume that neutral is close to ground 
voltage and safe to touch. It would break a few safety regulations for one 
thing -- mainly because a defective connection on that side of the cable 
would make the accessible metalwork live with only the effective 
resistance of the device to limit the current. That's unlikely to limit 
the current to a safe (for humans) level. 

-tony