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Thread: Potential Hazard in 70's Fender Convenience Outlet Wiring?!

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    Senior Member SoulFetish's Avatar
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    Potential Hazard in 70's Fender Convenience Outlet Wiring?!

    I've noticed after servicing a few silverface Fender amps, that they wire the polarized convenience outlet with the wrong polarity! At first, I didn't notice and wasn't aware of this. I had been disconnect the wiring to the outlet, just as an added safety measure. But, almost all of the ones that I'm servicing have the power chord wired directly to the outlet as a junction and they connect the hot (black) to the neutral terminal(the larger one), and the neutral to the brass terminal, which is designated for the hot connection. See below:




    Obviously, I've been rewiring it to modern standards, but what the hell's up with that?? What is standard course of action when these come into your shops?

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    Better Tone thru Mathematics bob p's Avatar
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    Excellent subject for discussion. Electrical safety is something that often gets glossed over.

    I've never noticed the backwards wiring before. And I'm the kind of guy who sticks an OSHA tester into every socket that I encounter. I'm wondering if the amps came that way from the factory. Are you sure that the amp hadn't been serviced previously?

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    Better Tone thru Mathematics bob p's Avatar
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    Something else that bothers me about that wiring setup is the lack of a jumper wire between the convenience outlet's ground terminal and the dedicated AC ground point on the power input to the amp. Optimally, you'd want to see a jumper wire going between the bolt where the AC ground comes into the chassis and the convenience outlet GND terminal, rather than using the socket's mounting bolts to provide a chassis ground. It's best if the ground path remains as low resistance as possible, so a direct connection would be best.

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    "Stand back, I'm holding a calculator." - chinrest

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    Supporting Member Jazz P Bass's Avatar
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    Odd.

    The Mid 70's Twin Rvb schematic shows the two blades as the same size.

    The late 70's schematic shows a wide (white wire) and a narrow (black) blade.

    mid70s100w.pdf

    late70s135w.pdf

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by bob p View Post
    I'm wondering if the amps came that way from the factory. Are you sure that the amp hadn't been serviced previously?
    That was the way the factory installed 'em. In recent times I'm often replacing the power cable on these amps, that gives me an opportunity to correct the situation.

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    don't forget the joker g1's Avatar
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    Not uncommon as Leo mentioned. If memory serves there is also a polarized 2 prong version that is usually wired up wrong and much more difficult to see by eyeball check. You have to put a meter on it to see which screw goes to which blade terminal.

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    Better Tone thru Mathematics bob p's Avatar
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    I have a little experience with UL certs, as I once filed a product safety complaint with UL for a Chinese manufactured GFCI that bore a UL certification, yet was unsafe. The result is that UL instituted a follow-up investigation that resulted in the product being de-certified and pulled from stores. It appeared that the manufacturer had modified the product after the product had received it's UL certification, which is a technical no-no. Any design change voids the UL certification.

    It's amazing that so many people report this bad Fender wiring as being typical. How did the amp pass the UL inspection if they were all wired the wrong way?

    Obviously, that didn't ever happen. The specimens that were sent to UL had to be wired correctly otherwise they would not have been granted UL certification. In cases like this what typically happens is that a manufacturer institutes a change in product manufacturing, and continues to slap the UL certification on the product. What they're supposed to do is to stop using the UL stickers because *ANY* design voids the product's existing UL certification and the product has to be re-certified.

    So one of two things happened: Fender changed it's wiring methods after the UL certification was obtained but continued to use the UL sticker even though the design change voided the certification, or someone just made a mistake in wiring up the chassis that was properly designed and QC failed to recognize the error. In either case, it seems that they were applying to the UL stickers to amps that were not UL certified. The question is whether they did this intentionally (fraud) or whether there was just a wiring oversight accompanied by sloppy product inspection.

    The amp in the photo has a yellow UL sticker but there's no way that the product could have received a pass from UL with the hot and neutral wires reversed in the specimen that was submitted for certification.

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    "Stand back, I'm holding a calculator." - chinrest

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    Supporting Member mozz's Avatar
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    I hope you are not going by colors and are actually testing to the plug end?

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    Supporting Member Steve A.'s Avatar
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    Quote Originally Posted by mozz View Post
    I hope you are not going by colors and are actually testing to the plug end?
    Good point but I don't recall seeing any 1970's power cords with colors backwards. Then again Fender always used black leads for ground in their strat pickups...

    Steve A.

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    Lifetime Member Enzo's Avatar
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    Black is a standard color for common in US electronics. In electrical wiring black is hot though.

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    Senior Member nevetslab's Avatar
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    I just had a SF Deluxe Reverb here in the shop a few days ago, and while I removed the Death Cap from the Grounding Switch, I didn't think to check the wiring of the AC Convenience outlet. And, to be honest, I never even thought to check and see that Fender had wired those correctly. Nothing like having blinders on, reyling on that UL Listed sticker!

    I'm wondering how many times UL inspectors caught that and other deviations during their periodic factory inspections.

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    Better Tone thru Mathematics bob p's Avatar
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    > I'm wondering how many times UL inspectors caught that and other deviations during their periodic factory inspections.

    I wonder too. Chances are that a lot of things slide by them.

    I remember reading a thread on the Carver Audio site where someone was concerned about their Sunfire amp not having a ground wire. They posted a pic of the amp's guts, and I immediately noticed a problem that everyone else had looked over for days -- the amp was wired from the factory with the mains fuse in the neutral limb of the power supply. What was most odd about that situation was that the amp had both UL and CE certifications.

    I was never able to figure out if the problem was a post-certification change or if the bad wiring went by unnoticed as the amp was examined by two different safety agencies.

    sunfire signature has no earth/ground? - Page 4 - CarverAudio.com

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    It does look like that by 1981 Fender was getting the convenience outlet wiring correct, at least on this 81 Fender Twin Reverb. I had to change the power cord on this amp since check of the neutral wire showed huge amounts of resistance. I snipped and cleaned the wire ends and no matter what the inner wire had corroded to the point of it being unreliable.

    Also, perhaps Fender employees in early part of 70's were use to wiring in 2 prong versions of the convenience outlet? Even then weren't many of those 2 prong sockets polarized with wider neutral? Then again back then how many 2 prong plugs were polarized? Lot's of questions to my post since I did not exist prior to 1978 .
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    Yeah, I always rewire it correctly, Ampegs too with the outlet.

    My 67 Pro Reverb is my go to amp for new venues as the power cord is usually long enough and the convenience outlet powers my rack gear (power conditioner, wireless and GSP1101) .
    Power cord and outlet were already replaced correctly when I got it.

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    Supporting Member loudthud's Avatar
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    Just worked on a 74 Super Six that had reversed connections to the convenience outlet. Original line cord with the red plug on the end that always has a broken ground pin. I debated just replacing the plug but I found a 10 foot extension cord that was the right diameter to fit the strain relief. Had to replace the white wire that goes over to the Polarity switch because it wasn't long enough to reach the neutral terminal of the outlet. What were they thinking with those terminals they used to solder the wires too? Job was a giant pain in the ass. Next time I'm just replacing the plug no matter how ugly it looks.

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    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personel.

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    Quote Originally Posted by DrGonz78 View Post
    Also, perhaps Fender employees in early part of 70's were use to wiring in 2 prong versions of the convenience outlet? Even then weren't many of those 2 prong sockets polarized with wider neutral? Then again back then how many 2 prong plugs were polarized? Lot's of questions to my post since I did not exist prior to 1978 .
    I just recall in my days before I knew better, it was a LOT easier to rip out the ground pin of the plug to fit it in a polarozed socker than it was to grind the polarized plug's wider pin down flat... so many houses I lived in where the sockets weren't polarized, let alone wired for 3-prong plugs!

    Justin

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    Supporting Member Steve A.'s Avatar
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    Quote Originally Posted by loudthud View Post
    Just worked on a 74 Super Six that had reversed connections to the convenience outlet. Original line cord with the red plug on the end that always has a broken ground pin. I debated just replacing the plug but I found a 10 foot extension cord that was the right diameter to fit the strain relief. Had to replace the white wire that goes over to the Polarity switch because it wasn't long enough to reach the neutral terminal of the outlet. What were they thinking with those terminals they used to solder the wires too? Job was a giant pain in the ass. Next time I'm just replacing the plug no matter how ugly it looks.
    With a little bit of glue you don't have to worry about a replacement plug separating from the cable. I recommend Helios light-cured adhesive which also has CA in for a double bond. (Link to follow if I remember...)

    Steve A.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by bob p View Post
    I once filed a product safety complaint with UL for a Chinese manufactured GFCI that bore a UL certification, yet was unsafe. The result is that UL instituted a follow-up investigation that resulted in the product being de-certified and pulled from stores. It appeared that the manufacturer had modified the product after the product had received it's UL certification, which is a technical no-no. Any design change voids the UL certification.
    That makes you a hero in my book If there were more people investigating and holding import goods accountable to US standards (not to mention the acceptable human and environmental debitage of manufacturing) our economy would be A LOT better off. As it is, of course, this is under the control of the government, which is under the control of the corporations. But this a different discussion. Still, you were part of the solution in this one thing. If all of us could claim that it would make a difference.

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