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Post subject: My Silver Face amps are about to electrocute me
Posted: Tue Mar 04, 2008 5:06 pm
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Can anyone recommend a good authorized Fender amp repair center here in Southern California, preferably in the Orange county or Long Beach area?

I have two Silver Face amps, a Deluxe reverb and a Super reverb. I'm guessing they are early to mid 70's. I inherrited them from an uncle that passed away. Anyhow, the problem is ..when plug my Strat in, within a minute I can feel electrical current running from the strings to my fingers. Sometimes it feels like sharp pin pricks. Also when I plug in my hollowbody, I can feel a pin $@!&# like sensation when the bottom of my wrist touches the bridge. This happens with both amps. I tried toggling the ground switches located in the back of the amp, but this made no difference.

Oddly enough, I plugged into a Silver Face Deluxe reverb at a local GuitarCenter using a Strat that I grabbed nearby and the same thing happend. I felt a slight shock in my fingers.

Is this a common issue with old Tube amps???

Thanks for any help you can provide.

-Chris


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Posted: Thu Mar 20, 2008 7:07 am
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Usually that happens when a house is old and has grounding problems. When you have a 2 prong plug it can shock you if you touch the amp and guitar at the same time but it seems like you have a grounding issue in the place your plugging the amps in.


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Posted: Thu Mar 20, 2008 8:30 am
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That's not exactly correct.

You're home can be perfectly grounded, but if your amp has a two-prong plug it is NOT using the building's ground (because the amp chassis isn't grounded through the cord) and will decide to use YOU and your guitar as a path to ground.

If you own an amp that has a two-prong plug, it's a death trap, no matter where you plug it in. If you have one that actually shocks you every time you plug into it, you're crazy for using it another second. Don't play through it until you have it brought up to safe standards by installing a 3-prong grounded plug (a job any amp tech can do easily).


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Posted: Thu Mar 20, 2008 10:04 am
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Jim is absolutely right. I've owned many 2 prong Fender amps the had the infamous "polarity switch." I've been shocked many times. It really hurts when you catch one on the lip from a mic. If it's a two prong cord, take it to a tech and have the amp properly grounded.


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Post subject:
Posted: Mon Mar 24, 2008 2:59 pm
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Last edited by tinker tech on Wed Jul 29, 2009 10:18 am, edited 1 time in total.

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Posted: Thu Apr 10, 2008 6:10 pm
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What I used to do, was just tie a stranded piece of wire, tie it around a screw of the chassis, then to the center screw of the wall outlet. A quick fix, but for all intense and purposes, a fully grounded 3 prong cable should be installed.


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Posted: Mon Apr 21, 2008 3:22 pm
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I am really glad you guys brought this up !!!

I just got off the phone with the amp tech I took my little Kalamazoo 1960's amp to and asked him to install a three prong cord.

I get shocked by everything it seems, so why take the chance.


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Post subject:
Posted: Mon Apr 21, 2008 8:29 pm
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If your amp zaps you just touching your guitar, there's something wrong inside that amp. God forbid you step up to a mic and complete mains power to ground. I've been on the receiving end of that more times than I can remember, probably because it fried my brain a little every time it happened.

Not only do you NEED to have your amp looked at yesterday, but you need to have it fixed permanently. Not only do you need a 3-wire cord added to your amp, but you need the "Death Cap" permanently removed from the power input stage of the amp at the same time. Any amp tech worth paying will know exactly what you mean if you ask about the "Death Cap". This will also remove the polarity switch. Nice thing about that is not only does it remove your guts from the electrical path of mains power, but leaves a hole for any number of cool mods you might want to consider doing to your amp without drilling a hole in a vintage chassis. This is pretty common with older amps where you'd like to try something like switching various parts of the amp's circuits, but don't want to screw with the value of a vintage amp.

Best investment I ever made in music in the last 35 years of playing for money was a wireless. No cord = no shocks. Period.

Cheers,
- JJ


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Post subject:
Posted: Thu Apr 24, 2008 7:14 am
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Last edited by tinker tech on Wed Jul 29, 2009 10:19 am, edited 1 time in total.

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Posted: Thu Apr 24, 2008 7:46 am
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One other little slick trick that should be done for a little extra safety when converting an old amp to a 3-prong cord is this:

When hooking up the wires for the cord, always make the ground wire much longer than required to reach where it needs to go. Make your other 2 wires only long enough to reach your transformer with just enough slack to work on the amp.

The reason is if for some reason your power cord gets yanked on really hard and pulls something loose inside the amp, the shorter power wires will come loose, but the longer ground will still be attached. If that happens, the power can still easily return to ground (path of least resistance) via the ground wire. Without this simple detail, ground will likely be your guts and you become the path of least resistance for power to ground. This can save your life in the case of an amp that gets knocked over for some reason while it's running and you're still playing through it. It doesn't happen often, but it does happen.

###

When I converted my old Twin to a 3-prong cord, I left the polarity switch in place, but wired it as an option to bypass the negative feedback circuit. That amp sounded awesome, but at 112 pounds with the JBLs in it, it was too heavy for me to haul around anymore. I recently traded it for a PRS CE22.

###

Cheers,
- JJ


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Post subject:
Posted: Sun Nov 01, 2009 10:14 pm
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Location: South Bay, CA
Death cap and 2 to 3 prong mod:
http://www.unclespot.com/3prongconversion.JPG

Amp repair in southern CA - Harbor Music in Redondo Beach. http://www.harbormusic.net/. They've done all the work on my Princeton Reverb as well as renovating my Bandmaster. Scott is great, fair and easy to work with. Also has a good supply of pedals, including Keeley and others.


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