What's that white stuff?

[Bob M.]

I'm wondering what's that white powdery stuff (no, not THAT white powdery stuff) I find in some of my older amps (and some older guitars), usually in and around the grounding. I know it's an electro-chemical reaction but what is it and what causes it? It it indicative of a poorly grounded circuit? It must be related to that stuff one finds on a car's battery terminals.

[Enzo]

Maybe be more specific or do photos
On a lot of old Fender amps of a certain era, the metal chassis was galvanized, and that coating breaks down over time leaving a powdery coating of zinc hydroxide.

[Bob M.]

In and around the metal capacitor housing on my Fender 1960 5F6-A Bassman. I rebuilt this amp about 15 years ago and it's been in heavy rotation about the last five years and I'm just doing a periodic bench check, re-setting the bias, checking the tubes, grounding, jacks, etc. Just a normal, routine maintenance check to make sure everything is ship-shape. It's been one of my most reliable amps. I have a Telecaster from the 60s that had that white stuff on the pots and switch that I wire-brushed off a while ago; same kind of stuff. But this white stuff doesn't appear on all older amp and/or guitars, just some. Is it related to the stuff one occasionally finds on car battery terminals?
Bob M.

[Enzo]

I don't know specifically what the battery spooge is under my car hood. So other than the result of chemical action, I can't say.

[stokes]

Stuff on car battery terminals is battery acid, not likely to find it in an amp.

[Leo_Gnardo]

Whatever the metal is, oxide and/or sulphide surface corrosion. Chloride too if the gear is in salty ocean breezes. It can depend a lot on what environment/atmosphere the amps' been used & stored in. Damp air, and air that cycles between damp & dry, tend to bring on corrosion. I've seen some awful corrosion in amps that have been stored in foam-rubber lined road cases. The rubber deteriorates and releases sulfur-containing gases which rust those amps something awful. And the owners packed 'em away in there thinking they were well protected. Not so much.

Surface treatment of the metal can have a lot to do with enabling or blocking corrosion. Steel that has that gold-looking finish tends to last well for instance. I don't know what that stuff is but it does seem to work. Anodizing of some sort? I expect a thin coat of oil would tend to stave off corrosion too. Break out the WD-40.

[J M Fahey]

Bare iron rusts in a jiffy, so some protective coatings are applied.
Most just separate iron from air: paint - varnish - nickel - chrome - etc. but zinc plating does double duty: besides physical separation, it also sacrifices itself, literally, by oxidizing itself *instead of* exposed iron.
All other coatings protect while intact, but if pores are present and inevitable scratches appear, exposed part will rust.

Zinc protects *even* the scratched area by electrochemical action, but turns itself into ugly foul sm3lling white powder.

Just wipe it out the best you can with a rag wet in clean water., better if distilled (car battery water bought at service stations)

Ships which of course float in salty water, *most*corrosive, incorporate a zinc "sacrificial electrode"go figure, think a solid brick of zinc bolted to ship hull.



They are inspected and replaced if necessary once a year..

[loudthud]

What is the goldish blue plating seen on Marshall chassis ?

[jack briggs]

What is the goldish blue plating seen on Marshall chassis ?

Chromate

[Chuck H]

What are the little blackish brown pellets shaped like rice grains I sometimes find in long disused amps?

[mozz]

Hantavirus pills.

[Leo_Gnardo]

What are the little blackish brown pellets shaped like rice grains I sometimes find in long disused amps?

Caraway seeds. I sometimes find them in amps that are in use. The owners must keep a spare sandwich crammed in the back, along with their bowling shoes, losing lottery tickets, worn out guitar picks, broken patch cords, obsolete set lists, spare change and who knows what else.

[nosaj]

Caraway seeds. I sometimes find them in amps that are in use. The owners must keep a spare sandwich crammed in the back, along with their bowling shoes, losing lottery tickets, worn out guitar picks, broken patch cords, obsolete set lists, spare change and who knows what else.

Not even close, I think he's talking mouse droppings.....
nosaj

[The Dude]

Hantavirus pills.

..

[teemuk]

My guess is solder flux (which is corrosive) and, uh, corrosion. It looks very much like the white acid stuff that leaks from batteries. And there most likely would be flux on a terminal connection to ease up with its thermal mass.