How do geet rid of corrosion on my 3rd Eico 720?

[w1vtp]

Found the power transformer for my third 720 (it was without one).  It was hiding in plain sight.  Anyway, the transformer is mechanically installed. Next will come the wiring.  This started out being a parts unit but it's all there, I think.  So, onward with a restortion.  I do not under stand why the rust problem.  I'll post some pics in a couple of posts just so you can see.

First installment.  Copper is gone and in its place ugly rust.

[w1vtp]

Next, some close ups of the rust

[w1vtp]

Finally, some switch corrosion. I used to use a certain abraisive rubber eraser years ago but that was like using sandpaper on he contacts  maybe someone has a better idea

The other two are working but I am trying to get rid of a slight hum.  I replaced the two filter caps with 47 mfd.  May I should up them to a higher capacitance.  Ideas?

Thanks, Al

[w1vtp]

Last pic.  Here are 720 # 2 & 3 bottoms up.  #3 will have the transformer transplant.  Just like doing a heart transplant.  #3 will live!

Al

[W2PFY]

Same problem on DX-100 chassis Al, don't know why it happens except to suggest that the platting was the bare minim used to keep costs down. I'm stripping a DX 100 down the the chassis to have the whole thing re-platted. I have a guy out west looking into the cost for me. I will have it plated extra thick or however they gauge it. Giving it more thought,  I think is just a dissimilar metal action going on for the most part.   

The black crap on the contact switches, is just silver tarnish. Happens on all silver plated stuff if it is exposed to the elements long enough. As a matter of fact, I have many coils for my Westinghouse MW-2 that are stored sealed in cans as large as a two pound coffee can and when I open them, the coils inside are black.

[w1vtp]

<snip>

The black crap on the contact switches, is just silver tarnish. Happens on all silver plated stuff if it is exposed to the elements long enough. As a matter of fact, I have many coils for my Westinghouse MW-2 that are stored sealed in cans as large as a two pound coffee can and when I open them, the coils inside are black.

What about a little Noxon on a q tip?  Then moisten another q tip with water and clean it off?

[W2PFY]

What about a little Noxon on a q tip?  Then moisten another q tip with water and clean it off?

Never tried to clean them to look like new Al, so I don't know what works best.

 Anyone else out there that knows the solution?  

[k4kyv]

don't know why it happens except to suggest that the plating was the bare minim used to keep costs down.

I think that explains it.  Just like the "copper clad" electric fence wire that has such a thin coat that, unlike real copperweld, within 6 months it begins to rust through.

The same thing happens with cheap hardware-store grade "zinc plated" nuts and bolts, compared to real hot-dipped galvanised hardware.

I would just clean off the surface rust the best I could and not worry about it.

[WBear2GCR]

For most silver plated electronic stuff cleaners like Noxon that are both abrasive and have chemical etchants, it's best not to use. Better to dip or use a cotton ball with something like Tarnex (there's a chemical name for what's in it but I can't recall...). The plating on electronic stuff is generally thin. (rinse thoroughly when done...)

I have learned that the black stuff is Silver Sulfide, not so good. I have also been told that silver oxide is actual more or less "silver" colored.

A milder but still abrasive polish is one of the pink ones found on the shelves in the supermarkets, but I'd avoid them too.

A possibility is "Nev-R-Dull" wadding, but I am not sure what chemical it uses...

                _-_-bear

[WBear2GCR]

Al, you could clean thoroughly and use a "brush plating" kit for the chassis. Of course you'd still have the same surface, just copper plated. Filling the pitting
would require multiple coats of copper followed by fine "sanding" with more coats of copper, until the surface is built back up.

Probably not worth it...

                _-_-bear

[N0WEK]

What I use on stuff like that is fine steel wool and WD-40, although with electronic stuff like that I'd use fine Scotch-bright. The WD-40 takes off the corrosion stains on the plating and leaves a protective coating on the metal. The first application gets pretty dirty, I just wipe it off with paper towels and use a second and maybe third application. With the last clean application I leave the metal wet and let it dry overnight.

For most things that I'm going to use this works great and protects the metal. For really perfect restorations you'd have to completely disassemble and re-plate.

[kg8lb]

 There is no way to really renew the finish by cleaning. THe corrosion has taken away plated metal and substrate. You can leave it, clean it or strip and re-plate. There is a copper paint (At the hardware store) however that has real copper metallic pigments that looks amazing and works well for spot touch up after cleaning.(Or complete re-finishing)

  If you re-plate and desire to make the plating very durable you must strip, metal finish then zinc plate the bare steel before applying the copper plate. Copper over zinc is very durable and resists corrosion well. No law against clear coating .

[w3jn]

I have learned that the black stuff is Silver Sulfide, not so good. I have also been told that silver oxide is actual more or less "silver" colored.

Indeed.  There is a lot of popular lore that the black stuff is just "silver oxide" which is a decent conductor.  It is actually silver sulfide which is a very poor conductor, and that is proven when you clean tarnished silver with Tarn-X and you get the rotten egg smell from the process, the Tarn-X liberating the sulfer.

De-Oxit on a q-tip works quite well for cleaning these switches.  Be sparing, don't get excited and spray the thing down - that'll pretty much ruin the switch.

[flintstone mop]

Al
Remember the dishwasher..........................

BAD idea?

[KM1H]

I sure wouldnt use De Wrex It.

I use a diluted TarnX on a Q-Tip and then wash off with brake cleaner that evaporates fast. Since TarnX is water based it is safer than may other products.

This thread reminds me... I have a real nice 720 but need a cabinet, anybody got a junker they are parting out?

Carl

[kg8lb]

 The Eico 720 switch is easily removed for cleaning. A good Tarn-X cleaning may then be flushed clean with distilled water. If you are careful, the same procedure works in place but removal allows for a better job along with a good inspection.

[WBear2GCR]

Tarn-X make ur own:



Thiourea              000062-56-6           5-7%
Sulfamic acid        005329-14-6           3-5%
Hydroxyacetic acid  000079-14-1    <1%
Citric acid                                           <1%

[WBear2GCR]

About Thiourea from wikipedia:

The LD50 for thiourea is 1 g/kg for rats (oral). A goitrogenic effect (enlargement of the thyroid gland) has been reported for chronic exposure, reflecting the ability of thiourea to interfere with iodide uptake.[1]

[ie. use rubber gloves...]

More from wikipedia:

Sulfamic acid is used as an acidic cleaning agent, sometimes pure or as a component of proprietary mixtures, typically for metals and ceramics. It is frequently used for removing rust and limescale, replacing the more volatile and irritating hydrochloric acid. It is often a component of household descaling agents, for example, Lime-A-Way Thick Gel contains up to 8% sulfamic acid and pH 2 - 2.2 [3], or detergents used for removal of limescale. When compared to most of the common strong mineral acids, Sulfamic acid has desirable water descaling properties, low volatility, low toxicity and is a water soluble solid forming soluble calcium and iron-III salts. Its also finds applications in the industrial cleaning of dairy and brew-house equipment. Although it is considered less corrosive than hydrochloric acid due to its lower pKa, corrosion inhibitors are often added to commercial cleansers of which it is a component. It is possible that the amino group could act as a ligand under certain circumstances, as does the chloride ion for Fe-III, when hydrochloric acid is used in rust removal.

Sulfamic acid is used in the S.C. Johnson & Sons, Inc. "Scrubbing Bubbles Fizz-Its Toilet Tablets", and in the Saeco Dezcal™ descaling powder for home coffee and espresso equipment.

    * Catalyst for esterification process
    * Dye and pigment manufacturing
    * Herbicide
    * Ingredient in Denture Tablets
    * Coagulator for urea-formaldehyde resins
    * Ingredient in fire extinguishing media. Sulfamic acid is the main raw material for Ammonium sulfamate which is a widely used herbicide and fire retardant material for household product.
    * Pulp and paper industry as a chloride stabilizer
    * Synthesis of nitrous oxide by reaction with nitric acid
    * In household cleaning chemical products such as Cameo.
    * The deprotonated form (sulfamate) is a common counterion for Nickel(II) in electroplating.
    * Easy-Off

[WU2D]

Gosh that all sounds too hard. Al - Just spray away - leave the tubes in

Mike

[kg8lb]

Gosh that all sounds too hard. Al - Just spray away - leave the tubes in

Mike

  Yep,That is the stuff I was talking about earlier in this thread. There is also a brush on version that levels out very nicely. It actually is very hard to tell the copper paint from the original stuff.

[w1vtp]

Mike, Gary

Sounds like a plan.  I like this.  I'll deal with the dirty switch with either my erasure or some silver polish.

Thanks, Al

[KC4VWU]

I've got one in the same shape, Al. I was thinking of totally stripping it, sandblasting the chassis, and then slowly working with finer grits of sandpaper, polish it for a copper quick plate. If that doesn't work out, WTH, I'll paint it. They seem to be a sturdy little tx.

73, Phil

[WBear2GCR]

The trick with the copper plating over pitting is the same deal as is done to rechrome pitted bumpers. Clean (etch clean ultimately) then plate heavy copper, then bring it back down to the steel, leaving the pits filled, THEN plate again with copper... that gives a flat surface. Otherwise you get plated pits. That could be a "nouveau" chassis finish though!

[kg8lb]

That is called copper buffing. Still not as durable as copper over a good zinc plate. Proper metal finishing on the steel followed by a zinc surfacing under the copper  will yield an excellent , durable finish. The copper paint also needs to go over a good surface. It will not fill pits and scratches. You may "lead" in the deeper pits with solder then sand to finish for a painted surface but not so with commercial copper electroplating.
  You can protect a polished , plated copper chassis with one of the automotive clear coats .

[KM1H]

Dont ever bring a lead based filler to a plater, you will be thrown into the vat

One way to save some plating and pit filling expense is do it yourself.  Take the chassis to the plater for a complete stripping and derusting. Discuss with him what you want to do to keep cost down.

Then silver solder (no lead content remember) or braze over the pits. Metal finish until the chassis is as smooth as a babys butt....or your girl friends....and bring to the plater.

Ive done my own grunt work on chromed potmetal and steel for both antique cars and radios for many decades as most shops wont be as fussy and the ones that are really get the big bucks.

Carl