Relay computers

[Gordon JC Pearce]

Tony Duell wrote:

> 
> There were/are also relays with 2 coils. The idea is that either coil 
> alone will activate the contacts, but if you energise them both together 
> (in opposite directions), the magnetic fields cancel out, and the 
> contacts don't operate.
> 
> And of course there are magnetically-latched relays (effectively SR 
> flip-flops).
> 
> -tony

And slugged relays, with a big metal ring in the coil.  These either 
delay opening or closing, but I can't remember which way round it works. 
  I've got a few from old telephone exchanges - when I was about 12 or 
13 I convinced my Dad to take a pickup truck full of BT phone exchange 
"modules" from the local scrapyard.

Gordon.