It's time to restore the 11/45.

Jon Elson elson at
Thu Feb 5 11:46:48 CST 2015

On 02/05/2015 10:27 AM, Noel Chiappa wrote:
>      > From: tony duell
>      > A plain Variac does not provide isolation from the mains so you are
>      > actually now working on mains-connected circuitry (read : dangerous and
>      > you can't clip a 'scope on it).
> I'm clearly a little slow this morning: why can't you use a 'scope on it?
Because the equipment under test is connected to the mains.  
A bridge rectifier is
between the AC input and the rest of the circuitry, 
therefore there is no part
of the EUT that is at neutral potential, and if you hook up 
a grounded scope, you
will have fireworks.  Floating a scope above ground should 
be reserved for the
most special cases where you are testing line-powered gear 
that MUST not
run on an isolation transformer, for some reason.


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