The Workbench

Better Living Through Not Getting Electrocuted


Not long ago, and in anther thread, I described becoming the proud owner of a vintage tuck-n-roll Kustom 150 guitar head. So vintage, in fact, that it had the stock 2-prong power cord and polarity switch to add a touch of danger to your guitar playing.

Having recently experienced the ground-fault zap treatment at a gig, I was eager to minimize the chances of that (or worse) happening again. So I sought to replace the cord with a grounded cord.

If you're going to replace a cord on a Kustom amp, the right thing to do is replace it with one that's at least 20 feet long like the original, and I settled for a 25-footer, an extension cord I cut the outlet end off. Now to open up the amp and see what I was in for.

I'd forgotten that they encased the components in a metal box, the build quality on these is amazing. It's no wonder so many are still in working order.

But wait, there's more! When was the last time you saw a schematic included with a piece of gear?

After consulting the schematic (and conferring with my EE friend Ben), I determined what needed to be done.

And it was pretty simple, even color-coded. Replace the white wire from the old cord with the white wire from the new cord, and the black one for the black one. Then find a suitable place to put the ground wire where it made a good electrical contact with the chassis (one of the terminal block mounting screws did a fine job of that). But first, remove the death cap

Another testament to the build quality, they could have just stuck the cap lead in the hole in the solder lug and soldered it, but no, they had to wrap it on each end and THEN solder it. In wrestling with it to remove it, one of the leads pulled out of the old cap. No worries, I wasn't planning to re-use it.

Now I've got a front-panel switch I can use for something else, maybe to turn on a set of chasing LEDs around the inside of the lip of the front panel. Some other time, maybe.

Anyway, once it was done:

And Ben approved of the work based on sending him the above photo, we were done. Except for winding that long cord onto the back of the amp.

Even 25 feet of 16-gauge 3-prong cord wraps easily onto those hangers Kustom was brilliant enough to include with their amps. Now I just HAVE to gig with it.

Oh, one other note. Ben, who sold me this amp, is helping its former owner's widow unload his guitar gear, and there are several more Kustom amps, including a Sidewinder combo with a JBL D130. He's even got some Kustom tube amps. Not sure my heart (or my back) is ready to become a Kustom owner again. But oh, the tuck-n-roll....


When did 3 prong become mandatory? I think thru '67 all the black panel Fenders still had 2 prong, if that is a reference point.


I think you're right as I have a 1967 Princeton here that still has a 2 prong plug and polarity switch.


My 1967 Gretsch 6157 Amp has a 2-prong cord with a single-pole, double-throw toggle switch.

Currently at the shop getting replaced with a 3-prong...along with other refurbishment.


Had a Gibson SuperMedalist with a 2blade plug and polarity switch back around '67, '68. Was playing at a friend's birthday party when a cute and rather inebriated young lady decided to give me a big sloppy kiss while I was playing, at which point we both got a pretty lively tingle. Guess the polarity was wrong; I just told her it was my electrifying personality.


I've got plenty of shocks from my '63 Fender Pro. When Savage Amps refurbished it a few years back, they put in a 3-pin cord and plug. They did a great job on the refurbish, I haven't had an electrical shock since.

What were they thinking in the old 2-pin days?



Better safe than sorry!

If you've ever gotten a tingle on your lips from getting too close to a mike while playing guitar, you'll appreciate a grounded circuit. Having dealt with thousands of amps of power on stage lighting and PA, I'm all for good grounding. You can't be too careful.


nice work, and smart move. Look at the way that transformer is held in place - six bolts! I guess if an amp weighs as much as a tank it ought to be built like one!


When did 3 prong become mandatory? I think thru '67 all the black panel Fenders still had 2 prong, if that is a reference point.

– DCBirdMan

I had the 2-prong on my '70 silver face drip-edge Princeton Reverb changed out a few years back. RIP Keith Relf.


You can't beat old Yankee engineering, that thing is built to survive a nuclear holocaust! Nice work, I'm glad you got it done. Getting zapped is no buneo!


It’s funny how after Fender went to the grounded power cord they kept the polarity switch and death cap. Guess old habits die hard.

Nice work by the way Frank. Can I send you some stuff?


Nice work by the way Frank. Can I send you some stuff?

Oh, I don’t think you want that, Ethan. I think I got lucky on this project. Every time I do a wiring project like this, I ask myself how my dad would rate my work, and usually the answer is that he would probably walk away shaking his head. He was a master of this kind of work and I wish I’d paid more attention.

On the topic of getting a charge out of playing guitar: A couple months ago we were playing a private party at a house, and in order to balance the electrical load, the bandleader plugged the PA into a different circuit from the one the amps were plugged into. One which may not have been wired correctly. I leaned into the mic during sound check and vaguely remember seeing a big blue flash (others nearby saw it, too), followed by a very quick review of my life, and then I had to go sit down for a while. I don’t want to do that again. I now carry a circuit tester for venues I’m not familiar with.

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