[Amps] Direct rectification of AC mains to drive the amp,

[Jim Thomson]

Date: Sat, 05 Oct 2013 21:48:15 -0700
From: Bill Turner <dezrat1242 at yahoo.com>
To: Amps <amps at contesting.com>
Subject: Re: [Amps] Direct rectification of AC mains to drive the amp,

ORIGINAL MESSAGE:          (may be snipped)

On Sun, 06 Oct 2013 00:44:46 +0000, Manfred wrote:

>Yes, sure!  But if you then connect the scope to a direct-line-powered 
>circuit, the scope chassis and knobs STILL will have a dangerous voltage 
>on it!  That's exactly the same as using an isolation transformer to 
>power the scope, or to simply use the scope's internal transformer for 
>insulation, and lift its ground. In all three cases the scope's chassis 
>will end up connected to the line through the circuit being measured!

REPLY:

I grant you the inverter approach is still dangerous, but not to an
experienced tech. The problem with all the above approaches is there is
still significant capacitance between windings of the isolation transformer
or the scope's power transformer and you are still lightly coupled to the AC
line. With the inverter approach, you have a truly "floating" scope. A few
stray pF maybe, but that's about it. 

Essentially a larger version of the Fluke ScopeMeter.  :-)

73, Bill W6WRT

##  use an outboard isolation xfmr.. like a  low C 120 vac to 120 vac type..to feed the analog scope.
Then you end up with two transformers nose to tail. The outboard isolation xfmr, and also the
Xfmr inside the analog scope.   The end to end stray C is very low.   The C between the isolation
xfmr is in series with the C between the pri + sec of the internal xfmr. 

##  I like my Fluke scope meter.... has never let me down. 

Jim   VE7RF