weather effect protection of vintage hifi?

[adeel]

I have more than 10 vintage amps some are late seventies and some eighties . Most them having small trasistors legs becoming black and little weak due to rust . These trasistors test ok and work good in amps . I tried to clean their legs and they becomes clean and some start showing red copper material .
I noticed that after some time they becomes black again no matter how you clean them their feet become black again .
My question is how to stope them becoming rusty again i mean if some type of glue which does not effect their performance can be placed from printing board to plastic of trasistors . So what is the solution to save them from wheather effect which has no harms on sound quality ? Thanks

 

[RVT1K]

Manufacturers will often "conformal coat" pcb's that will be exposed to harsh environments.

Something like this: https://www.digikey.com/en/products/detail/techspray/2108-12S/10440573

But there are lots of options.

 

[jhjove]

The one issue with these older devices is just that they are old. Some materials used were not meant to last forever and quality control is probably starting to show.
The leg rust/corrosion is probably occurring within the transistor package as well. Not saying for certain; but there is a chance.

Read up on "Tin whiskers" and the issues from electro-migration.

 

[adeel]

Manufacturers will often "conformal coat" pcb's that will be exposed to harsh environments.

Something like this: https://www.digikey.com/en/products/detail/techspray/2108-12S/10440573

But there are lots of options.

So sir can we use silicon to stop more damage i mean if transistors are encapsule in silicon provided they don't heat then can we stop more rusting and any impact on sound quality? Does conformal coat impact sound quality ? Thanks

 

[trinhsman]

No ex

So sir can we use silicon to stop more damage i mean if transistors are encapsule in silicon provided they don't heat then can we stop more rusting and any impact on sound quality? Does conformal coat impact sound quality ? Thanks.

No expert here, but IMHO, any coating applied would need to be ABSOLUTELY non conductive in any way. I think it’s possible, just not sure what would be used and how it would be done.

 

[elnaldo]

I think the rust will be going it's way into de transistors at some point... I'd start thinking in transistor replacements instead of weather proof coatings.

Anyway, there is a product called "liquid electrical tape" that could serve your purpose.

 

[RVT1K]

So sir can we use silicon to stop more damage i mean if transistors are encapsule in silicon provided they don't heat then can we stop more rusting and any impact on sound quality? Does conformal coat impact sound quality ? Thanks

I have only seen conformal coating used on new assemblies. If the legs are simply oxidizing after being cleaned, I think the conformal coating would help. If, like some are suggesting, the corrosion is inside the transistor and leaching out then I don't think it will help.

But conformal coating is made to be applied to electronics and I've seen it used on some very sensitive circuits, don't worry about conductivity or having any impact on sound. One thing that can be considered a negative is that repairs are more difficult on a board that has conformal coating on it.

 

[adeel]

Tha

I have only seen conformal coating used on new assemblies. If the legs are simply oxidizing after being cleaned, I think the conformal coating would help. If, like some are suggesting, the corrosion is inside the transistor and leaching out then I don't think it will help.

But conformal coating is made to be applied to electronics and I've seen it used on some very sensitive circuits, don't worry about conductivity or having any impact on sound. One thing that can be considered a negative is that repairs are more difficult on a board that has conformal coating on it.

Thanks a lot sir for giving me useful knowledge and valuable time .

 

[adeel]

Thanks elnaldo , trinhsman , jhjove and all friends .

 

[gadget73]

The black probably is an indication that the legs may have been silver plated originally. The black is I think silver sulphide? Its not something I'd worry about honestly. If the transistor is going to fail, painting magic goop on the legs isn't going to do much for it. I also don't really see where the black on the legs means much. I've replaced transistors with shiny legs and had perfectly good ones with black flakes on the legs.

this stuff is a half century old, and it was not really engineered to last this long. Sometimes things just fail because their time is up.

 

[RVT1K]

Tha

Thanks a lot sir for giving me useful knowledge and valuable time .

You are very welcome.

 

[Bill Ferris]

FWIW, A possible, inexpensive and very easy to implement coating of the oxidizing transistor leads, IMO, would be to completely coat them using "clear" fingernail polish very shortly after re-cleaning.

Where is this receiver being used that this high humidity type moisture rich environment exposure that would cause this apparently rapid re-oxidation, it would seem not in a very climate controlled environment ?!