SS hardware, aluminum chassis, and grounding

[Blooze]

So I got to reading about safety ground and galvanic reactions between dissimilar metals which I'd never considered. I'm sure this has been covered before, but I've only found a little on it and still had some questions, so please indulge me

In my tube amp builds (hifi and guitar) I've typically use aluminum chassis and 304 (18-8) stainless bolts, star washers, flat washers, and nuts. I sand the inside of the chassis where any ground connections are made right before I tighten everything down. Safety ground I'm using a star washer (or keps nut), then a flat washer if not using the keps, nut, solder tab, star washer, flat washer, and double nuts (or another keps). Other ground points like circuit ground I'll use a star washer, flat washer (or solder tab), and nut. I also do at least one transformer bolt with a star washer between the frame and chassis, and another inside the chassis before putting a nut on. I have used just a star washer, solder tab, and nyloc for safety ground a couple of times though which I'm now questioning. OCD and what-ifs suck.

Should I go back and replace the ground hardware with normal zinc plated stuff? It'd be a PITA, but not the end of the world. I'm always jumpy about the safety grounds in particular as I'd never want anyone getting hurt

I’ve posted the question on the few forums that I’ve gotten good help over the years from.

[glass54]

Hi Blooze,
Aluminium Chassis (very Clean) and 304 SS screws is my choice. SS304 flat washers with SS304 compression washers for all mounting screws is a standard for me, esp Tube sockets. SS304 hardware is a little more expensive BUT I purchase in bulk (boxes of 100 or 200) and I can purchase them from a local supplier.
Mains earth wire is 4mm SS with lug and star washer. I like to mount the Transformers with star washers and kept nuts.
In my engineering experience, Aluminium and SS304 is a safer place to be than Al plus Zinc plated stuff.
A little OCD is good but one must learn to control it ( ) I think paying attention to neat/effective workmanship is a good thing.
Keep up the good work and a photo is always welcome
Kind regards
Mirek

[Blooze]

Hi Blooze,
Aluminium Chassis (very Clean) and 304 SS screws is my choice. SS304 flat washers with SS304 compression washers for all mounting screws is a standard for me, esp Tube sockets. SS304 hardware is a little more expensive BUT I purchase in bulk (boxes of 100 or 200) and I can purchase them from a local supplier.
Mains earth wire is 4mm SS with lug and star washer. I like to mount the Transformers with star washers and kept nuts.
In my engineering experience, Aluminium and SS304 is a safer place to be than Al plus Zinc plated stuff.
A little OCD is good but one must learn to control it ( ) I think paying attention to neat/effective workmanship is a good thing.
Keep up the good work and a photo is always welcome
Kind regards
Mirek

Thanks Mirek. I think I’ll leave it alone for now. I have some OCD that involves neatness, but being officially diagnosed it’s very much a doubting and what-if mental game that drives the compulsions. I have a form called pure-O where most of my compulsions are mental at this point. I actually refuse to work on mains wiring or plumbing for my home now due to fear of causing some sort of damage. Even though when I was younger I had no problem doing those tasks. A flip switched about 10 years ago and everything changed. Causes much anxiety and fear that has to be worked through. I still get a bit anxious at times about tinkering with amps, but it’s manageable so far and it lets me practice my therapy suggestions.
Sorry for the long winded explanation.

Shane

[stratomaster]

It's an interesting game. Dissimilar metals can lead to galvanic corrosion and using all 300 series stainless can lead to galling/cold welding. Compression washers are ineffective at best under most reasonable amp torques (white papers in this topic are a very interesting read, if you're into that type of thing), so that pushes us into toothed washers, k lock nuts, or nylock. Toothed washers are preferred for ground applications.

The thing to keep in mind with the galvanic series is that the presence of an electrolyte (salty humid air, typically) is required for this effect to manifest.  A climate and humidity controlled environment is unlikely to pose an issue.  And with galling, a metallic antiseize (Mg or Cu) can keep this from occurring.

[Bluebark]

I use dielectric grease. It does a good job of sealing out the oxidizer. About 20yrs. ago a buddy turned me on to it when I decided to rewire my boat. Connections made at that time are still in the same condition. I have spent my whole life turning screws and nuts in both automotive and computer industries and can't ever remember running into an issue where bi-metallic corrosion caused an issue in climate controlled conditions.

[Blooze]

I use dielectric grease. It does a good job of sealing out the oxidizer. About 20yrs. ago a buddy turned me on to it when I decided to rewire my boat. Connections made at that time are still in the same condition. I have spent my whole life turning screws and nuts in both automotive and computer industries and can't ever remember running into an issue where bi-metallic corrosion caused an issue in climate controlled conditions.

I had my wife pick up a small tube of Noalox when she went to the city yesterday. I know dielectric grease is good for corrosion, but I’d be wondering if it would be appropriate to use when your looking for good electrical connection such as for a safety ground point since it’s an insulator?

I know Noalox is for aluminum to aluminum or copper, but its zinc based so figured it cuts through aluminum oxide it should work decently with zinc based hardware.


I’m sure I’m thinking way to much into this and the likelihood of using SS hardware for a ground connection being a problem in an amp that never goes anywhere and stays in a conditioned house is minimal. But this OCD issue really pushes my buttons once a “what-if” has latched on. Bane of my existence. 

They say brass is terrible to put in contact with copper, but I have an amp that used brass everything hardware (except for the safety ground) that I checked and still get 0.0 ohm readings from the IEC ground tab to any bolt on the chassis. I made that amp at least 15 years ago and there’s zero visible corrosion. Anecdotal example of one.

[Bluebark]

I deal with OCD every day of my life. Probably have 100 unfinished project as a result of the OCD...I forget what the Doc called it but I get hung up on the minutia of a project until it grinds me down and I have to move on. Anyway back to the oxidation. For the last 20yrs before I retired I worked in Data Centers and have torn into more boxes than I care to remember, some going back to Big Iron days. The only oxidation I ever found was on silver coated power connection but it never caused any issues. Like Stratomaster said...it's the moisture that is the issue. IMO

[Willabe]

As posted already, Noalox anti-oxidant compound.

Use internal star washers, 1 on each side of the chassis (inside/outside), use 2 nuts jammed/tightened together with 2 wrenches. The washers teeth cut into the chassis when tightened and lock out air. This greatly helps stop/stops oxidation, if the bolt/internal star washers/nuts stay very tight.   

Clean the parts well with fine sand paper or emery cloth 1st. Then apply the anti-oxidant compound on all parts that come in contact with the chassis and the chassis itself.

[Blooze]

Thanks. When I haven’t used a tooth washer, then solder tab, and a nylock nut I’ve done it as Rod Elliott describes only with a solder tab. I feel more confident with Rod’s example. Now I know that Noalox is helpful I’ll probably go back and redo some of the ground bolts (PE, circuit, and transformes) with it and zinc plated hardware. It’s only a few bolts per amp so no biggie really.

[Bluebark]

Let me ask a question, do you all find a lot of issues with grounds in the radio/amp world?

[acheld]

Let me ask a question, do you all find a lot of issues with grounds in the radio/amp world?

Not with the connection itself.   

Design of the grounding system is another story.

[Blooze]

Well, I swapped out one bolt each on the transformers, the circuit ground, and safety ground. I went through two bolts on the safety ground because these zinc coated soft steel ones strip easy. I ended up using a torque screwdriver on that last one and torqued it 18 in/lbs which seemed to be what most manufacturers had in their charts for carbon steel 8-32 bolt. Truss bolt head, tooth washer on the outside, then tooth washer, flat washer and nut torques to chassis. Then another flat washer, solder tab, tooth washer, flat washer, and two nuts stacked and torqued. Used a little film of Noalox under the tooth washers that contacted the chassis for insurance. I can periodically check the ohms between the input jacks and IEC and tube socket metal or transformer bells and the IEC to prove to myself that the safety ground is still good. Was showing 0.0 ohms to everything that is exposed.

My what-if anxiety caused by OCD is still raging, but it is what it is. Enough that I’ve decided to step away from messing with tube amps or mains voltage any more (I’ve built 6 so far (3 from scratch and the rest kits). Selling all the parts and stuff I still have to make any over the next month mostly over at Diyaudio. The anxiety is not worth it to me. If it gets worse and I can’t get it sorted with therapy I’ll part the amps out I have and sell that off. The fear that something I’ve made may hurt someone else, including my family, in any way, is debilitating for me.  I hate this condition.

Thanks for all the advice and schooling over the years. I’ll still pop in to ask questions about the stuff I still have.

[Bluebark]

WOW...you guys torque your grounds? These things are That critical?

I always just used German torque specs...goodnnuff.

Blooze, here is some advice from one OCDer to another. Do Not let the disability grind you down. I know it seems impossible sometimes but it IS doable. When the itch gets to be bad...I just walk away and work on something else. You obviously love working on amps...no one does something for years if the hate it. Also, if you decide to give my solution a try, go do something that is the complete opposite of what you were doing. Micro to Macro or vice a versa. So the next you're working on an amp and feel the monster start to creep in, go cut the grass or weed the garden or anything else of that nature. No reason to walk away from something you love to do!

Besides...fixing/building amps is not rocket science. So don't sweat it...the sun will still rise tomowwor!!

If there's one thing I've learned, giving in to a disability only make it worse.

[Blooze]

I don’t usually torque anything but gun scope bolts. Unfortunately just when I thought these were goodntight they suddenly weren’t. I’m sure I was just trying to get it tight as possible (because tighter is better in this case, right?) and stripping them. So out came the torque screwdriver to keep my ham fists in check, lol.

I’ve never had the ability to walk away and do something else for a while then come back to it when my OCD is involved. I used to do some plumbing and electrical around the house for 35 years or so. Now, I can’t even think about doing it without having a panic attack. Even after therapy. So I pay pros to do it and then worry about how well they didn’t do something. Unfortunately it’s not something I can control. Don’t know why it came on 10 years ago, but it did, and it always revolves around safety (fire, flood, electrocution).

[Bluebark]

When I lost my father to the war in VN at the age of nine, I became very insecure. Mother threw me in therapy for years, not much help. What finally cured me was getting my ass kicked in school. Kids are cruel (glad they don't run the world) and I was an easy mark. It didn't take long...

If safety issues issues send you over the edge. Let someone else do that and then not worry about it.

[Willabe]

Blooze, I sent you a PM.