Risk of galvanic corrosion of dissimilar metals in bonding the chassis to Earth?

[SoulFetish]

The problem with connections between copper (or stainless steel) and aluminum (or silver) is the formation of copper oxide and/or aluminum oxide, which can be lessened by the use of an antioxidant paste containing zinc particles, like Penatrox. The zinc acts as a "sacrificial" anode to protect from the galvanic action between the dissimilar metals.

If you like to use stainless steel hardware on aluminum chassis (I do), you can place a zinc washer between the aluminum chassis and the stainless washer/bolt/nut, and it should last even longer.

The formation of copper and aluminum oxides is greatly enhanced by the presence of oxygen, so sealing the connection (with clear coat paint or even liquid plastic or rubber) is the last line of protection, even if you use zinc to reduce the corrosion.

Do all three of these things, and you can play your amp outdoors at the beach for decades

Great stuff, Ken. I dig it

[Tom Phillips]

...Do all three of these things, and you can play your amp outdoors at the beach for decades...

Perfect!

[g1]

Perfect!
[ATTACH=CONFIG]40532[/ATTACH][ATTACH=CONFIG]40533[/ATTACH]

Back in the days before photoshop, I imagine they actually got a stuntman to do that surfing photo-shoot ?

[Tom Phillips]

Back in the days before photoshop, I imagine they actually got a stuntman to do that surfing photo-shoot ?

He is holding the guitar as if he actually knows how to play it too.

[The Dude]

Is that Dick Dale?

[Tom Phillips]

Is that Dick Dale?

I'd say no. Dick Dale is a lefty.

[The Dude]

I knew it wasn't. Just a bad attempt at a surf guitar joke.... Apologies.

[KevinOConnor]

Hi Guys

The chassis is only supposed to be a shield NOT the audio signal interconnection medium.

The chassis should be hard-connected to the AC safety ground. Use a toothed solder lug or washer to assure galvanic connection. I use all stainless hardware in my amps, with stainless pems and a mix of stainless and aluminium sheet. No problems with loss of ground bonding between panels or to the mains ground with amps that have shipped around the world.

No need for sticky substances between or around the pems.

Have fun

[SoulFetish]

Hi Guys

The chassis is only supposed to be a shield NOT the audio signal interconnection medium.

The chassis should be hard-connected to the AC safety ground. Use a toothed solder lug or washer to assure galvanic connection. I use all stainless hardware in my amps, with stainless pems and a mix of stainless and aluminium sheet. No problems with loss of ground bonding between panels or to the mains ground with amps that have shipped around the world.

No need for sticky substances between or around the pems.

Have fun

You install stainless steel pem nuts in aluminum panels?? Why would you do that? I can understand some of the examples above of people using stainless hardware in aluminum chassis because they can isolate the two metals and maintain the superior corrosion resistance of two types of metals. I doubt a zinc compound would even offer much with pems, because the aluminum cold flows around the pem during install. Also, a toothed solder lug or washer do absolutely nothing to prevent galvanic corrosion if the metals were exposed to any electrolyte. Look, honestly, i think you are leaving yourself and your product vulnerable to a potential failure down the road. I would recommend reading Ken Moon's post above, he offers sound advice for protecting against environmental conditions, which we, as builders, have no control over.
Lastly, in most cases, identifying the point of failure in an electrical safety device ( like the earth connection in a guitar amp ) Usually results from a forensic investigation. I guess I'm wondering, how would you know that none of your amplifiers have a compromised earth connection?

[J M Fahey]

The protective grease avoids contact with air but mainly humidity.

It is dielectric as in non conductive, not because it´s "between two unconnected metals" for the very good reason that they are very well connected, in intimate contact and with as low resistance between them as possible, so no capacitor there by definition.

I deal with it regularly, it´s liberally used on Telephone Company connection panels, where it´s squirted on every interconnection on the post/roof/outside wall panels, which are exposed to heay rain and condensation, let alone dust and freezing 24/7/365

It´s not used on simlarly placed 220/380V mains connection boxes, because high voltage and current involved can easily burn and carbonize it and make a worse mess, also high voltage/current involved punches through any corroson buildup, unless suck power junction box was left unused and in a corrosive environment for years, but at low audio voltages and very low currents involved in Phone signal trnsmission, even a little corrosion can be a mess, hence the extra protection.

Phone Company is so used to it, that even connector boxes meant for inside home use are also coated in such grease, I sometimes replace or add one and my fingers and tool tips get slippery.

It´s whitish translucent and might very well be some kind of silicon grease, VERY sticky, next time I meet one of them I´ll ask for some.

Yes, I have found rusty, to be more precise greenish (copper corrosion) or whitish (zinc decay) chassis connections in 40 or more y.o. equipment , and a few exaggerated cases when sea mist was involved.

One of them was an Ampeg SVT400 where *all* surface to surface contact was red rusted, lthough to the naked eye it did not look that bad; I think the chassis rack was spray painted after assembly (I mean the empty rack cabinet) so it got paint on visible surfaces but not between them, which wouldn´t be *that* bad, but this particuar band lives on tour all year long and I guess it got salt spray on Coast towns and lots of rain or condensation in between, I never saw such a bad one.

As always, they were on tour and in a hurry, so my emergency solution was to drive a plain nail between all mating chassis surfaces to make (temporary) contact and bring it back within 15 days, when they would pick up some of my amps (all built on aluminum chassis).

When they brought it back, I fully disassembled it, left the naked (iron) rack cabinet and sent it to my galvanizing guys.

They basically boiled it in a VERY NASTY cyanide based witches´ brew (the reason I do not Galvanize at home, only process I set up for and abandoned) which removes absolutely all oxide and paint, and then applied a thick layer of Marine grade Zinc plating; then chassis was epoxy dust painted.

It ended looking just as the original, only without any silkscreening, just strips of paper painter´s tape written with Sharpie.

All mounting hardware was replaced, of course, and got covered in a dab of transparent Nitro lacquer.
Still looking new, 15 years later which with this band is a lot.

Now, what do you think about this Hiwatt 300W Bass Amp?

It´s property of a Tour/Holiday company, and it was used 50% of the time on a cruise ship, other 50% by the sea, but only sent to servicing when the power amp exploded:

[J M Fahey]

...

[Jazz P Bass]

That is one butt ugly amp.

Maybe they should spray conformal coating on all of there equipment's circuit boards.

[KevinOConnor]

Hi Guys

Conformal coatings are used in lots of applications from security systems to satellites. I don't particularly want to ship sticky chassis or ones with sticky goo inside to players who might open them, or for techs to have to deal with. The coatings that dry hard make the equipment unrepairable in most cases, asnd that seems worse than risking some corrosion - although I prefer to avoid both if possible.

I have not seen or heard any issues about stainless steel and aluminium being incompatible. I know there are all different grades of both materials and likely the magnetic forms of stainless are a problem? Anyway, I've seen no issue with the chassis of this type I've shipped in the past 30+ years. On the other hand, the original painted steel chassis did have problems, mostly related to the paint not being applied properly by the vendor. That was why i switched to stainless in the first place.

I like the Japanese chassis that seem to be galvanised and then very well painted.

Have fun

[Ken Moon]

Thanks for your thoughtful answers, Kevin. I have a ton of respect for your body of work and your knowledge.

Admittedly, I worked in Naval aviation for 35 years, and witnessed many, many nightmares related to galvanic corrosion, from "red plague" (copper oxide) that destroyed miles of wiring harnesses in A-6 aircraft, to the more recent multi-million dollar SNAFU with the second LCS ship off the assembly line, where unprotected steel met the aluminum hull (the first LCS off the line used a steel hull, and didn't have this problem).

As far as stainless steel and aluminum in particular, aluminum is the "anode", and SS is the "cathode". A tenet of design to reduce bi-metallic corrosion risk is to keep the surface area of the "cathode" (SS) as small as possible in relation to that of the "anode" (Aluminum).

So SS bolts/washers in Aluminum plates/chassis is much less troublesome than vice-versa (that's why using aluminum rivets on steel plates is a big no-no).

What anti-corrosive compounds with zinc particles do is act as sacrificial anodes, greatly reducing the formation of oxide on the surface of the aluminum plate/chassis. Zinc washers do the same thing.

The final step of sealing out oxygen could be considered as a minimum risk abatement, as it works very well, but relies on proper application.

It's probably a reasonable compromise to go ahead and put zinc washers on bolts as a general practice, and a quick spray of clear coat or a dab of liquid plastic/rubber seals the deal.

Using the anti-corrosive compound could be skipped to avoid any possible mess - I mentioned it mainly to explain what it does, and also to offer it as part of a fool-proof process for those who live or play in extremely humid/wet environments.

Cheers,

Ken

[KevinOConnor]

Hi guys

Ken, that's good info. And you work in a really harsh environment!

As far as I know, no one has taken any mortar shots at my amps.... so far....

I prefer all stainless chassis but pressing in the larger pems can be a challenge. The one shop that did everything as I needed it TIGed the pems after pressing them in. Unfortunately, they fell victim to the recession. For smaller bolts like 4-40 the stainless sheet can be tapped and that works well. I'll have to consult with my current metal guy.

Have fun