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Do columbia 202's have any pot metal?
Posted: Sun Mar 19, 2017 4:45 pm
by 12jslater
Such as the back bracket or anything else?
Re: Do columbia 202's have any pot metal?
Posted: Sun Mar 19, 2017 4:50 pm
by gramophone-georg
No sign of any pot metal on mine.
Re: Do columbia 202's have any pot metal?
Posted: Sun Mar 19, 2017 5:15 pm
by 12jslater
cheers i'm just going to service mine and I wanted to know if there was anything I should be weary off.
Re: Do columbia 202's have any pot metal?
Posted: Mon Mar 20, 2017 6:16 am
by Phono48
They certainly do! The complete inner horn, from the base of the arm to the point at which it "swivels" is made if pot-metal. The most common problem with this, the 201, and the 112 are breakages of the pot metal joint at the base of the arm.
Re: Do columbia 202's have any pot metal?
Posted: Mon Mar 20, 2017 8:21 am
by epigramophone
The end of the long thin pot metal horn pivots on lugs with the larger tin horn. These lugs can break and are tricky to repair.
Having re-attached the broken lug with super glue, I have successfully drilled through the entire assembly and inserted a threaded rod secured with lock nuts at both ends. Even if the lug breaks again, the rod should still hold the assembly together.
It is a pig of a job, and had my 112a (ancestor of the 202) not been the brown crocodile version I would have scrapped the machine.
Re: Do columbia 202's have any pot metal?
Posted: Mon Mar 20, 2017 5:15 pm
by 12jslater
Is there anything to do to preserve them such as coating the entire pot metal section of the horn in epoxy?
Re: Do columbia 202's have any pot metal?
Posted: Tue Mar 21, 2017 12:00 pm
by Phono48
I've never tried, but I don't think it would do much good. When the pot metal backs on HMV No.5 soundboxes expand, they often break the brass fronts, so I would imagine with power like that, a coat of thin epoxy would be useless.
Re: Do columbia 202's have any pot metal?
Posted: Wed Mar 22, 2017 8:49 am
by Marco Gilardetti
To the best of my knowledge, pot metal "pest" is not typical only of zamac but descends directly from the use of zinc, which decrystalizes in presence of lead impurities in the alloy. The process is accelerated by humidity, but aside of keeping the item in a dry place there is no other way to prevent or arrest zinc pest, as the original compound of the alloy obviously cannot be changed or purified.
For small objects with principles of pest I've seen someone immersing the object in cyanoacrylate glue, that will fill by capillarity even the smaller and invisible cracks and will help keeping everything together. Of course for big objects such as the elbow of a horn, a cyanoacrylate bath may be impossible to do.