I've just bought a 1969 Fender Dual Showman (silverface). Thing is, 3-prong outlets were introduced on these models in early 1970.
I've been shocked quite a few times with it, nothing really bad but holy shit! I'm not ready for this.

I went to get a surge protector, basically an extension cord that indicates if everything works fine or not, but still got shocked like a mother****er.

Then I guess, the problem might be in the Amp head. Could it be a loose ground wire ?
You need to convert it to a 3 prong plug. Any tech should be able to do this for relatively cheap.
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I used to plug a mic in a tube head. Getting shocked from it SUCKED! Thats why I'm glad I wasn't the vocalist that had to deal with it. It got fixed when the guy I bought it from replaced the end
Thanks for the quick answer.

There's also a switch ground on the back of the amp.
Theres A, Off, and B

Thing is, it works great but there's a risk of electrocution when I flick the switch
The ground switch places a small capacitor between neutral and ground to suppress any noise present on the mains. They had a switch to change what wire it switched the cap to because with a two prong lead the active could be on either pin. The idea was you put the switch in the position that cut the most noise.
Even with a two prong plug you shouldn't be getting shocked, both sides should be isolated from the chassis. Get a three pin plug installed, sure, but make sure he addresses the underlying fault that is placing voltage on the chassis. Stop using it until you get it sorted.
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