Re: Remote Power Supply Connection

Iain Churches wrote:
> 
> "Patrick Turner" <info@[EMAIL PROTECTED]
> wrote in message
> news:482AE4E2.FFC2B37D@[EMAIL PROTECTED]
> >
> >
> > I still find ordinary octal sockets are the most reliable and easily
> > fixed
> > way of terninating umbilical cables.
> 
> Agreed. They were good.
> 
> > Ilegal now in most places, but then if you do it right for yourself
> > there
> > isn't any more danger than a normal mains cable wire.
> 
> The reason it seems is that one can pull the plug out partly
> and touch the live pins on the cable connector.........
> >
> > http://www.turneraudio.com.au/300w-amp-images.html
> 
> ......except in the way that you have ****elded them.
> Good solution!  I have seen the same thing done using
> a black plastic capacitor clip.
> 
> Regards
> Iain

It would be a rare occasion when cables were not plugged in properly
because the amp won't work properly,
but with flanges and winged machine screws to screw down the plug,
it would ensure connection, like the way a monitor plugs into a PC box
at the rear.

The danger is when a plug is removed from a PSU and some idiot
immediately
grabs the pins , therefore touching pins connected to 
charged up capacitor within the amp and an earthy pin. These charge
voltages take time to 
sag down to safe low levels.

But it can be a very quick time if all you have is say 2uF of plastic
caps within the amp
chassis for the B+/B- rails and then have all the large electros and
chokes in the PSU unit.

The 2uF will shunnt the inductance of 2 mtres of cable length from amp
OPT CT to PSU
where the thousands of uF lurk to be a lowZ voltage source at LF. 

My 300 watters will incor****ate this safety improvement in future
because there is spare room inside 
the PSU enclosures. ( Not much though because there is a huge PT and a
large choke... )

The 845 amps have considerable C in the amp because of the room
available and discharge due to 
anode current rapidly pulls down the +/- 600V rails, but once the 
cathodes of 845 go cold from no supply, the pull down effect 
reduces before the rails have come down to safe levels.
So I have put diodes on +/- 600V pins inside the amp, so only backwards
leakage
current through the diodes can flow.
However, there are 4 pins in one octal plug for two floating ac supplies
which are biased at the 845 cathode
voltage at -450V approx. Diodes cannot be used to stop back flow.
Dificult to explain here,
so I have to use some relay switched cap discharge resistances to
discharge the 
offending voltages.
I will probably settle for a screw and plate to clamp the plugs into the
psu, and if that screw isn't 
fully wound in the psu cannot be turned on due to a pressurer switch
located where the screw is.
So once someone tries to unscrew the cable plug clamps, the psu will
turn off,
and voltages will sag before they can fully turn the clamp screw out to
pull the plugs out.

One has to be practical, and place obstacles which act like padded walls
in the way of idiots.

Laws, signs and warnings don't do much to save lives, judging by the
toll re****ted daily.

Patrick Turner.