Upgrading 2-prong plug on vintage amp to 3-prong?

[EllenGtrGrl]

As a budding EE and musician in 1957 I built myself an amp. When I started gigging and found myself onstage with several amps & a PA, I realized that death by electrocution would be an ironic exit for someone with my aspirations. In those days, long before grounded outlets were a thing, I decided on a defensive measure, building this:

Attachment 88159

It's just a neon pilot light with two 25' test leads. I had couple of slip-on alligator clips to hold things in place if necessary, and used it faithfully after setup to test for voltage between my stuff and everything else on stage. Found many dangerous situations over the years. Finally retired it after all equipment and venues were three wire, but I still carry an outlet tester and plug-in GFCI that I use for outdoor gigs or indoor gigs where I'm on the end of an extension cord of unknown origin, or where I'm picking up noise that suggests a missing ground. I'm long-retired from an engineering career, but still have no intention of death by electrocution.

Danny W.

Ah yes! A GFCI. I've used them once in a blue moon on the past. I've also just used a cheap multimeter, to measure the voltage between my guitar strings, and the amp, or if I sing, the microphone - especially after I got a poke in my month a little under 30 years ago, the first time I stepped up the mic to sing (and play guitar) at a gig. You don't mess with grounding issues.

[Little Jay]

Quick question. When changing it to a 3-prong, is it necessary to rewire the grounding? Or simply replacing the cord as-is, and having the ground-prong be a "dummy" simply to get the direction right work out?

Dude……. You need to connect the ground wire to the amp’s chassis, otherwise you might just as well leave it ungrounded! Preferably with a dedicated bolt secured with a star washer and lock-tight so it will never lose connection:



You can leave the ‘live’ and ‘neutral’ wires as they are. With a properly grounded amp it doesn’t matter how it’s plugged, live and neutral can be switched around in the wall outlet (overhere in the Netherlands we don’t have a ground pin, we have two grounds on the side in the wall outlets).