Best Grounding Caps

From priver–(at)–ivera.com Sun Jul 9 23:40:58 CDT 1995
From: priver–(at)–ivera.com
Newsgroups: alt.guitar.amps
Subject: Shocks and Grounds
Date: Sat, 08 Jul 95 19:26:19 PDT
Mime-Version: 1.0

I just tuned back into this group and noticed postings regarding shocks.
There was some excellent advice given to use 3 wire cords and retrofit
vintage amps with them. I also advise changing the grounding capacitor
to a modern type, no more than .01 mfd, rated at 250 VAC, and it should be
DVL or preferably an XY type. RIFA from Finland and WIMA build the safest
Caps fro use across the line. The leakage current should always be measured
after doing this (if possible). The orginal .047 Paktrons were not DVL rated
until the late 70’s. I have also seen so many old Vintage MArshall with
extrtemely leaky grounding Caps. Cut them out or upgrade them.

If you choose to keep your polarity switch, when you upgrade to a 3 wire
AC Mains cord, change the switch to a SPDT Center Off, and preferably a 15 A
HD Switch, please no Asian Radio Shack for this spot on your amp.

Best regards,

Paul Rivera

From mcguir–(at)–orld.std.com Sun Jul 9 23:41:43 CDT 1995
Newsgroups: alt.guitar.amps
From: mcguir–(at)–orld.std.com (Monte P McGuire)
Subject: Re: Shocks and Grounds
Date: Sun, 9 Jul 1995 07:58:39 GMT

In article , wrote:
>
>I just tuned back into this group and noticed postings regarding shocks.
>There was some excellent advice given to use 3 wire cords and retrofit
>vintage amps with them. I also advise changing the grounding capacitor
>to a modern type, no more than .01 mfd, rated at 250 VAC, and it should be
>DVL or preferably an XY type. RIFA from Finland and WIMA build the safest
>Caps fro use across the line. The leakage current should always be measured
>after doing this (if possible). The orginal .047 Paktrons were not DVL rated
>until the late 70’s. I have also seen so many old Vintage MArshall with
>extrtemely leaky grounding Caps. Cut them out or upgrade them.

By ‘changing to a modern type’ I hope you mean changing its connection
>from “neutral to chassis” to “hot to neutral”. There is no reason to
have a capacitor from neutral (or hot) to ground in any circumstance.
At best, you will only increase the amount of power line induced
clicks and hum in the amp.

Applying a capacitor (properly rated as you state above) across the
hot and neutral lines will most often have a beneficial effect: high
frequency normal mode trash that would normally pass through the power
transformer to the secondary will be attenuated by such a capacitor
and no safety hazard is created by their use. Such a capacitor will
also have no effect on the leakage current from the chassis to the
line… no need to measure it because it’s a transformer problem, not
a line capacitor problem…

(Sorry to be so draconian, but people occasionally suggest that shunt
capacitors from either or both side of the power line to ground are
good; they do filter some power line trash but that also _couple_ a
lot of power line trash too and sometimes create nasty (i.e. lethal)
chassis potentials.)

Happy pickin’,

Monte McGuire – N1TBL
mcguir–(at)–orld.std.com

 

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