A leaky Tube Amp? The horror!


Well-Known Member
Hey folks, more of a discussion question, We recently had some talent come through that brought all their own tube based gear, in this case some "artisanal" stuff with "made specifically for X" (the artist using it) nameplates.

Unfortunately, a ground connection came loose at one of the plug connections between the amp and the main panel, which we figured out *after* the talent went to play a chord while their lips were on the SM58, and got a nice zap about 76VAC measured between the guitar string and mic body. The cable was promptly replaced, and then repaired. I was a bit too distracted to think about getting a current reading, but it must have at least been above 5mA, the talent was quite vocal about how unpleasant it was.

Here's the question, in the year 2024, why do we still tolerate equipment that doesn't have any meaningful isolation between mains and meaty bits? These amps were not ancient, these were relatively recently made units.

Personally, I'm half tempted to pull out a GFCI whenever someone shows up with tube gear like this from now on, though I'm curious on what everyone else thinks about this whole type of issue.

Am I overlooking something? Genuinely curious about what others think.
Yes. Power to back line instruments and their AC using ephemera should be protected by GFCI.
I can relate. In the early 1970s, being too lazy to fix the mis-wired standby switch, on my Ampeg Gemini VI, I ran a ground wire from my amp, to the PA, to my brother's guitar amp. One day my brother forgot the ground wire to his amp. We started our first song, and as my brother stepped up to the mic, he immediately got knocked on his butt. He lived (still lives), but sat out the rest of the night. He reminds me of that night, from time to time.

I fixed the amp the following day, and never knowingly put anyone else in a potentially dangerous situation since.

I have been in several rehearsal studios, and felt the unwelcome tingle on my lips, from a poorly grounded room.
A colleague of mine told me of a time he and his band were rehearsing and the lead guitarist got a shock off his guitar. It was only when he fell over that he broke the circuit. He said he was convinced he was screaming for help. The rest of the band said he hadn't made a sound and the first they knew was when he collapsed in a heap. 240V mains bites.

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