# RCA Metal Can Transistors, how to process?



## NobleMetalWorks (Dec 6, 2012)

I have a large amount of old RCA Resistors.


> I meant Transistors here not Resistors


 I have never run this type of material before and would like advice on how to process these.

Here are some pictures:












All of them have some gold plating, most of them are fully gold plated and as you can see, the bottom lid has been removed from some of them and most are gold plated inside and out.

My questions are... 

Is the only PM value the Au?

What is the best way to prepare them to be processed? Some of the smaller ones do not have a bottom lid, but have a resin on the inside that I have no idea how to remove unless I did so by incinerating or wet ashing neither I am a fan of.

If I get them cleaned up I figure I might be able to run them in a sulfuric cell, but I am not sure what metal the can is made of. If it's too much, I might not process them but through them up on ebay instead.

Any help would be greatly appreciated.

Scott


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## etack (Dec 6, 2012)

hey Scott I believe they are kovar metal. kind of a pain with little gain. I would burn crush and use nitric on them. Or sell them if you have enough.

Eric


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## NobleMetalWorks (Dec 6, 2012)

etack said:


> hey Scott I believe they are kovar metal. kind of a pain with little gain. I would burn crush and use nitric on them. Or sell them if you have enough.
> 
> Eric



Thanks Eric, I appreciate the response.

Scott


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## g_axelsson (Dec 6, 2012)

They are called transistors, not resistors. It have been talked about before and I think there are numbers of typical yield too.

Go through these posts an I think you will find something useful.
https://www.google.se/search?q=site%3Agoldrefiningforum.com+metal+can+transistor&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial

/Göran


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## NobleMetalWorks (Dec 6, 2012)

g_axelsson said:


> They are called transistors, not resistors. It have been talked about before and I think there are numbers of typical yield too.
> 
> Go through these posts an I think you will find something useful.
> https://www.google.se/search?q=site%3Agoldrefiningforum.com+metal+can+transistor&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial
> ...



I knew they were transistors, I have no idea why I typed resistors, thanks for the correction and the threads.

Scott


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## Geo (Dec 6, 2012)

i wait until i have enough to keep me busy for a few hours. i use a pair of diagonal cutters and crimp right above the solid plate. the cap normally pops right off. it may take a little practice to get it right. the yield is pretty decent, i ran about 4 pounds through AP one time and i think i reclaimed around 3g of gold.


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## NobleMetalWorks (Dec 6, 2012)

Thanks for the information Geo...

I have a lot of this type material, I was thinking about trying what you are talking about, with nippers. I'm afraid I have hours and hours of work in front of me.

Scott


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## stardust18 (Dec 6, 2012)

SBrown said:


> I have a large amount of old RCA Resistors.
> 
> 
> > I meant Transistors here not Resistors
> ...


As mentioned, it is possible to release the bottom of diagonal cutters. If you do not have time, you can stop and completely, but will be increased consumption of acid. Dissolve best in a mixture of dilute sulfuric and nitric acids. Good luck.


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## NoIdea (Dec 7, 2012)

Another thing i am working on is material very similar to this, try placing the bottom portion of the transistor into a soldering tray, or just "tin" with solder all the visible gold, then heat, allowing the solder to migrate/defuse into the gold and underlying substrates (copper/nickel), place into a shallow container, now moisten with old AP solution, it can dry out butt try and keep it damp, not soaked.

Oxidation of the solder will also remove the gold as gold powder, give it a go, it works as long as the solder diffuses properly. You will save on nitric and or hydrochloric digest acids. Just wash the resulting mud to recover your gold. And you end up with a sizable chuck of saleable base metal.

Cheers 

Deano


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## Geo (Dec 7, 2012)

Deano, those things are a real pain, but they do contain good gold and for me its worth the effort. theres gold under the cap. as much if not more than on the bottom and the wires. there is a set of gold bonding wires that connects the chip to the legs. the cap has to come off or your only getting half the gold. too, theres a grease under the cap like lithium grease.white, thick and slick.it makes a mess of everything popping those caps off. i boil mine in water and dish soap but that only goes so far (the first batch i did, i used gasoline to get it off :shock.


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## scrappile (Dec 7, 2012)

Geo said:


> Deano, those things are a real pain, but they do contain good gold and for me its worth the effort. theres gold under the cap. as much if not more than on the bottom and the wires. there is a set of gold bonding wires that connects the chip to the legs. the cap has to come off or your only getting half the gold. too, theres a grease under the cap like lithium grease.white, thick and slick.it makes a mess of everything popping those caps off. i boil mine in water and dish soap but that only goes so far (the first batch i did, i used gasoline to get it off :shock.



It's Thermal grease for helping with heat dissapation'

http://en.wikipedia.org/wiki/Thermal_grease
Silicone oil-based thermal grease can be removed from a component or heatsink with an alcohol (such as rubbing alcohol) or acetone


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## goldsilverpro (Dec 7, 2012)

TO5s and TO18s (the smaller ones) are one of those items that have progressively been cheapened over the years. If they are all magnetic kovar, including the lids, you can put them directly in 50/50 nitric without taking them apart and end up with gold foils. Probably need a little heat.

You might read this thread. Arthur got 4.7g/pound from the batch he ran. Some of the newer ones have no gold plating on the base and have aluminum lids. They may contain no gold.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=34&t=5535&hilit=transistors


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## NobleMetalWorks (Dec 7, 2012)

Thanks GSP I really appreciate the pointers and the thread.

I have a lot of this material. Of the ones I have, all have some gold plating, somewhere. They are all out of old amplifiers. I have run finger boards from the same material from the same scrapper that have yielded almost twice what I was expecting, the fingerboards are white with wide gold plated fingers, the gold pins I have run from this same material were silver with gold plating over 50% not the entire pin, but still I recovered more than I do normally from more modern pins that are totally gold plated. I suspect these should have a good yield if they follow suit with the rest of the material I have been receiving from the same person.

I am going to try your suggestion GSP, I just don't have any time to sit and crack these open one by one, I would but there are way too many of them. 

Scott


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## Aristo (Dec 7, 2012)

I have several hundreds of pounds of the boards pictured.They are pre 1970s.I have been wondering about the yields on the transistors, and based on testing , the 4.7g/lb seems conservative. These appear different from the ones mentioned by the OP.


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## NobleMetalWorks (Dec 7, 2012)

I think your material will yield more than the material I have, you have the gold leads still attached, the material I have was cut from the boards, the gold legs almost don't exist.

I'll post my yields here in this thread when I am finished.

Scott


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## goldsilverpro (Dec 7, 2012)

Aristo,

Nice stuff! Lots of money there. There are lots of different metal configurations on these "top-hat" transistors and lots of different values. The best I've seen were very old ones that were painted black. If you find any of these and scratch though the paint on the lid, you will likely see gold plating.


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## Sucho (Dec 7, 2012)

Guys.I run this type of material very often.the yield runs from 4 to cca 20 g / kg depending on manufacturer, year etc.most common yields are between 7 and 9 grams per kg.

They are kovar based and its horrible to dissolve it in nitric.it takes ages and needs a lot of heating.

I prefer straight AR way.kovar dissolves in AR easily.the only thing you have to achieve is to have all metals in highest ox. State.it is visible on loaded AR colour.if not, you will loose lot of gold that is metallic colloidal because of cementing on undissolved kovar and few other reactions.

Precipitation is without problems.dissolution is always vigorous, be careful.


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## goldsilverpro (Dec 8, 2012)

Sucho said:


> Guys.I run this type of material very often.the yield runs from 4 to cca 20 g / kg depending on manufacturer, year etc.most common yields are between 7 and 9 grams per kg.
> 
> They are kovar based and its horrible to dissolve it in nitric.it takes ages and needs a lot of heating.
> 
> ...


In the 70s, I worked for a refiner that literally ran tons of these in nitric. He used a large steam-jacketed 304 stainless kettle, if I remember right. He could do a big batch in a day.

When I have run these or other kovar items, such as gold-lidded CPU packages, in nitric, I ran them in heavy duty stainless containers (about 5 gallon size) with a lot of heat. I put about a 3"-5" layer of parts in the container, covered them about a half inch over the parts with 50/50 nitric and heated the solution quite hot. As they dissolved, I added concentrated nitric in increments to drive them faster. I stirred occasionally. When the solution level was about 2" above the parts, I stopped adding nitric and let them work hot until the reaction was almost nil. I have noticed that, when dissolving most anything, the dissolving slows down when the solution gets too deep - the parts are down there and the acid is up here. I usually stop at 2" over the parts. I then diluted the solution back to about 50/50, stirred it, let it cool to where I could safely handle it, poured off most of the solution, and started over with fresh 50/50 nitric with subsequent concentrated nitric additions. After doing this fresh nitric thing 2 or more times, depending on the amount of parts I started with, all the kovar was gone. Several batches of fresh acid on a single batch of parts really speeds things up. I would guess it takes about 4 to 5 hours if you keep at it. After pouring off the last nitric, I rinsed a couple of times, transferred the gold/garbage residue to 4 liter beakers and used aqua regia.

I have used this "starting with lots of material and using several batches of fresh acid approach" on quite a few other things - the direct dissolving of karat gold as an example. It does speed things up and you can start with a lot more material in a container.

If you don't want to go through all this until all of the kovar is dissolved, try to get, say, 80-90% of the kovar dissolved in nitric, dilute to at least 50/50, let it cool, and pour the solution off carefully. Then use the aqua regia in big beakers. You'll end up with a lot less gold solution that way.

A guy I knew bought gold CPU packages by the drum load. He used fairly warm aqua regia diluted with about 40% water, to tame the AR down a bit, and used SO2 gas to drop the gold. There was a lot of nitric left and it took a lot of SO2. Also, with the weak AR, the kovar went fairly fast, but it took forever to get the gold braze under the chip and he seemed to always leave some behind. You need full-strength AR to get that gold with decent speed. Even then, it takes quite awhile.

Admittedly, AR is faster. I like to use nitric first because I end up with a much smaller amount of material to dissolve in AR and I also end up with a lot less gold solution to deal with. Also, when using AR to start, what sort of container do you put it in when you have a large batch? About the only thing would be glass or, maybe, titanium. A big steam-jacketed, glass-lined Pfaudler would be perfect, but not too many people have one of those. Most people would be limited to 4 liter beakers, which wouldn't hold much if you didn't want it to foam over. If you first get rid of all, or most, of the base metals with nitric, a beaker will hold quite a bit of gold residue.

Either a gallon of 70% nitric or a gallon of aqua regia will dissolve about 2 pounds of kovar.


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## NobleMetalWorks (Dec 8, 2012)

Originally I was going to try a stripping cell and now I am wondering if maybe dilute sulfuric might do the trick. Would either of these methods work?

I just want to mention that if anyone attempts to make diluted sulfuric to remember two very important things. First, you never pour water into acid, always acid into water, and in this case it should be done very slowly. Also it should be done in the correct receptacle, there is a lot of heat generated. Second, it should be done in a well ventilated area, the acid vapor given off is white in color and will make sulfuric acid when it comes into contact with water/moisture. Since your lungs are like a sponge and are really filled with fluid/water, you can imagine what creating sulfuric acid on your bronchi would do to a human. 

Scott


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## goldsilverpro (Dec 8, 2012)

SBrown said:


> Originally I was going to try a stripping cell and now I am wondering if maybe dilute sulfuric might do the trick. Would either of these methods work?



On these parts, the silicon chip is usually attached with a gold/silicon eutectic braze preform. Although the chip is small, the braze is about 20 times thicker than the plating and it therefore can contribute considerably to the overall value. The sulfuric stripper won't dissolve this braze and or most any other gold alloy and, even if it would, it could only eat the braze from the edges of the chip, which would take forever. To get this braze you need AR to work its way underneath the chip.

Although I have never tried it, I have heard of using hot 10% sulfuric to undermine and separate the karat gold layer from the stainless on gold-filled watch bands. Sounds iffy to me, but who knows? If that worked on these parts, you would have the gold foils intermingled with the undissolved kovar and, I would think, that would be a mess that could only be remedied with nitric and/or aqua regia.

Kovar is 54Fe, 29Ni, and 17Co. I don't think the sulfuric will do much dissolving by immersion, no matter what the strength or temperature. Anything is worth a try, though. 

With a porous cup set-up (a fizzer cell, sort of), you could put the cathode (probably graphite) in the cup and put the parts, as the anode, in a weak sulfuric sulfuric solution, in the tank surrounding the cup. I know the weak electrolytic sulfuric will dissolve the kovar. Instead of a porous cup, you could partition the tank with an anodic membrane, which only will pass anions. The problem I've found with these is that, with all the fizzing, the air in the room soon becomes full of H2SO4 unless you have a fair-sized powerful fume hood.


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## NobleMetalWorks (Dec 8, 2012)

I think I am going to do a bit more reading before I process these. I also think I might attempt two different methods to see which works better for this particular lot.

I appreciate all the help, and once I process I'll go ahead and post what I do here.

Scott


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