Dissimilar metals and grounding.............

[Jack_Hester]

Amp chassis' seem to come in a small mix of materials, steel and aluminum being the two primary types.  Here at the power plant, we have to be very careful of bonding of dissimilar metals.  In previous times, we used a thin layer of paste called 'No-Ox'.  My father was an electrical contractor, and used another brand made by Ideal, but I don't remember what it as called.  In recent years, we use a synthetic bearing lube, as it has the same effect as the 'No-Ox' had, preventing oxidation when two dissimilar metals are joined.  Steel on steel, and steel on copper, don't seem to have as much problem with oxidation as aluminum on any other metal does.

Now to my point.  With grounding being a major issue in amp chassis', for safety reasons as well as a good path for current flow, I wonder just how much of a problem builders have had with this.  Particularly with aluminum chassis'.  It is my intention to continue the practice of applying a very thin film of synthetic lube on the bare metal surface that I plan for components to have a good ground.  Like grounding lugs, or penetrations in the chassis where pots, jacks, switches, etc., will be mounted.  Probably most amps remain in some environment where oxidation may not be a problem.  But, I would think that those who perform with their amps (meaning they are hauled, stored, and played in every imaginable temperature and moisture combination) would or should be concerned with such.  

Also, dissimilar metals bonded together will create a very small current flow, especially as temperature changes.  Under normal circumstances, this is nothing to be concerned about.  But, it may have a noticable effect in amplified signals.  That's the way thermocouples work, to generate a signal to measure temperature.  Two dissimilar conductors are joined, with a known voltage generated for any change in temperature, and can be measured when a meter/instrument is connected to the other end of each conductor.

Comments?  Maybe this is old news, but I didn't find any posts directly addressing this.

Jack

[sluckey]

Bonding a copper ground wire to an aluminum chassis is not likely to cause any problems for a guitar amp. Precautions do need to be used in the electrical field for any 'current carrying' wires such as line or neutral though because over time the connection will become resistive and heat up, possibly becoming a fire hazard. I think you can forego the grease if you use lugs that are rated for CU/AL. You are usually dealing with aluminum wire and steel lugs when using grease.

[RicharD]

As an electrical contractor myself, I have seen the problems associated with al/cu connections.  There's an entire neighborhood here in Austin that was built during the Vietnam era and they are all wired with aluminum.  I've learned to take my little temp probe with me to find the hot receptacles.  I've never seen any problem like this in an amplifier.  Grounding issues I've seen in old amplifiers are: failure due to relying on rivets, Fender eyelet boards buckling  and pulling ground wires loose, and just plain ordinary loose connections.  As for corrosion, I've seen a lot of green PCB from stuff being left in a garage for a decade, but never anything associated with simply dis-similar metals.

[jojokeo]

In my water quality profession, running a reeftank for years, owning various boats & living by the ocean - galvanic corrosion occurs much faster & aggressively in a watery environment. I haven't seen near the rate or issues w/ this on any of my amps or other electronic or instrument gear as long as it's kept inside. But the moisture created even by doing laundry in the garage w/ it closed up will really accellerate corrosion on tools, vice, and other equipment. Moisture is the devil when it comes to any type of corrosion. Water depts use transition fittings, a reeftank uses a titanium ground probe but for the chassis it makes me think of using a small piece of sacrificial zinc anode somewhere? 

[Jack_Hester]

As I am new to tube amp building, I will probably make comparisons to my work, more often than not.  As our boiler controls are all computer-based and completely digital out to the I/O modules, signal noise is hardly an issue.  However, from the I/O modules to the field instrumentation, the analog signals are  24vDC, 4-20mA.  Back when the process controls were all analog, signal noise would drive us nuts.  Digital seems to filter the signal out of noise (or the other way around) completely.  But, I still practice the old habits of trying to clean it up in the field as much as possible.  This is the reason I initiated this topic.  I'm thinking that it is not as much an issue with amps and musical instruments being in close proximity, as would be with the instrumentation that I deal with being hundreds of feet from the processor. 

Anyway, I'm watching closely how the members here build, as I want to follow suit as much as possible.  Some of my practices will more than likely be way overkill.  And, may not even apply at all.  But, I'm thinking that some will, to processed (amplified) signals.  I'm glad it gave cause for comment. 

Jack

[Tiny_Daddy]

When I get a bare aluminum chassis, it gets sent out for a conductive clear Iridite conversion coating. Great stuff, no chromate, no color dye, good paint adhesion, good corrosion resistance. The plating shop charges by the batch: 1 chassis or more, $50.

[Frankenamp]

+1 when water is involved Long time ago some "genious" tried to save a little money using copper QC couplers on copper pipe... the fix was very expensive.

[Fresh_Start]

OK so I'm using Doug's terminal rings plus lockwashers.  What are they made of and should I do anything more than scour the chassis right around the hole for the bolt?  (either aluminum or steel chassis)  Never heard of putting some kind of grease down.

BTW living in Virginia may not be as humid as Florida, but it sure ain't Arizona either

Chip

[jojokeo]

what kind of grease - antisieze, dielectric, lithium, silicone, bearing, or maybe just use Dumble's goop sealer?!? 
(sanded and/or heated steel metal (from drilling) gives long term concerns but you should be okay)

[Jack_Hester]

Never heard of putting some kind of grease down.

So far, I haven't read of anyone using any kind of 'no-ox' paste/grease on amp chassis'.  That's why I started this thread.  Looking at the materials used in amp building, particularly grounding, I began thinking of the possibility of issues.  Mainly with aluminum chassis'.  The mention of joints 'becoming resistive' is the very issue that we see at the plant.  To stay more in line, though, with amp building, my concern was how to keep a good conductive mechanical grounding joint.  Some people use a cloth to apply the grease/paste.  I use a finger to apply, and wipe it off.  The film left behind appears to be no more than just moist.  Both on the lug and metal surface that the lug is attached.  Usually, an ohmmeter cannot measure the joint resistance.  Stays that way for a very long time.

what kind of grease - antisieze, dielectric, lithium, silicone, bearing, or maybe just use Dumble's goop sealer?!?

The paste/grease that we use these days is a 100% synthetic gear/bearing lube. 

Jack

[Frankenamp]

On the old amp chassis I been playing with, the steel lugs and bolts can rust a bit, but I haven't seen much trouble with the connections that are just good 'ol lead solder connecting the lug, wire or strip to the chassis. The rivets usually have a dollop of solder on the underside to hold 'em. I'm thinking yer new best friend is gonna be a nice big 80-100 watt chisel tip iron.