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 Post subject: RCA 100 A speaker
PostPosted: Sep Fri 12, 2003 12:03 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 591
Location: Emporia, Kansas USA
Has anyone ever had a problem repainting an RCA 100A metal speaker cabinet? I have tried cleaning it with several things.I have even sanded it in places. The spray paint still bubbles up in several places both inside and outside. It is not the paint cuz I tried it on other things.<P>------------------<BR>Robert


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 Post subject: RCA 100 A speaker
PostPosted: Sep Fri 12, 2003 1:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4007
Location: Malone, New York USA
<BR> Hi Robert,<P> A very common problem with these.<BR> <BR> I've resorted to glass beading or very fine sand blasting. This was the only method that seems to clear the housing of oxidized die-cast material, making it ready to paint.<P> If the housing were sanded thoroughly and a spray sandable primer/sealer applied first, (Duplicolor or similar) -and resanded before applying top coats, this should help.<P> Den<P>------------------<BR>


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 Post subject: RCA 100 A speaker
PostPosted: Sep Fri 12, 2003 7:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 591
Location: Emporia, Kansas USA
Thanks Dennis, Didn't know what I was doing wrong. <P>------------------<BR>Robert


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 Post subject: RCA 100 A speaker
PostPosted: Sep Fri 12, 2003 7:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6576
Location: Freeport, LI, New York 11520
Just a quick question,Dennis....<BR>I have a half a dozen of these pot metal cases waiting to be done and I've noticed that metal chunks are literally popping out of the skin of the cases..they're not being banged around since I've had them, but I would find a chunk of pot metal laying next to the case every so often....downright wierd!...any thoughts?....Jim<P>------------------<BR>


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 Post subject: RCA 100 A speaker
PostPosted: Sep Sat 13, 2003 4:13 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 30698
Location: Pocasset, Cape Cod, MA
Pot metal swells from corrosion at the grain boundaries if the wrong alloy was used. With such a large piece of pot meal changing size, a lot of stress can build up. A friend of mine years ago was repainting one of these, and had heated it to dry the primer or something. He heard a loud boing and a piece several inches in diameter flew out of one side and across the room.<P>Bubbling is common, caused by air trapped in the corroded areas. There's not much you can do about it. Reducing temperature variations might help, or using the fastest-drying lacquer.<P>------------------<BR>


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 Post subject: RCA 100 A speaker
PostPosted: Sep Sat 13, 2003 4:30 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 37677
Location: Livermore, CA
Hi<P> I've tried all kinds of paint on RCA 100A speakers. Even after you think they look good may still bubble over time. A chemistry teacher was was trying to find a way to neutralize the reaction but haven't heard anything recently.<P> Tried using a porous paint and also the opposite, epoxy seal. Neither worked. Some R100A castings still bubble. <P>------------------<BR>Norm


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 Post subject: RCA 100 A speaker
PostPosted: Sep Sat 13, 2003 5:22 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 6576
Location: Freeport, LI, New York 11520
Alan....<BR>Would there be any way to possibly anneal the case at,say, below half the distance to melting point and ambient? (or should I say stress relieving)....Jim<P>------------------<BR>


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 Post subject: RCA 100 A speaker
PostPosted: Sep Sat 13, 2003 9:01 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4007
Location: Malone, New York USA
<BR> Based on my own experiences,the paint bubbling problem is best addressed by using the _slowest_-drying finishes possible.<P> Good surface prep and plenty of time for any preparation solvents to completely evaporate.<BR> The surface may not look porous, but it is.<BR> <BR> This is the time to have some dry warm (not hot,) heat on the housing, to flash off any trapped preparation solvents before applying primer or top coats.<BR> Then, let housing cool to spraying temperature.<P> Ambient spraying temperature is important.<BR> The cooler and less humid the better- and not in the sun.<P> More heat reduces flow-out, causing the necessity to lay on more or heavier coats to achieve the desired finish.<BR> The surface of the paint "skins" over, then the trapped gasses come through from below. <BR> Keep it cool, light coats, sufficient time between coats.<P> Long-term adhesion of paint system to the housing is a consideration.<BR> Zinc-chromate primer is good for this, but getting difficult to obtain, so I've substituted Duplicolor primer. Seems to work OK.-So far. Just a thin coat.<P> Good luck with it, <BR> Den <P>------------------<BR>


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