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Can silicone glue, when used to hold say, an orange drop cap in place, cause a detrimental effect on the signal? I ask because after doing a Silverface Bandmaster-to-bassman 6G6-B mod, the sound I was getting was ratty with an evil rocks-in-a-can type decay. I narrowed the problem down to the driver stage. The input was clean, but the output was nasty. I suspected a connection problem, which meant re-soldering the eylets, which meant soaking up the old solder with braid to make sure there were no globs of solder underneath the fiberboard. I had to remove a sizeable amount of silicone glue holding the orange drops in place in order to pull the cap leads out. When I was done, I tried the amp out without gluing the caps in place, and the amp just SANG. Thus, the question.
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I strongly suspect the stuff can get conductive over time. Had this Bassman 135 from a friend, someone had "repaired" it before. The silicone was everywhere, not just the preamp - bias board, caps in the doghouse, PI, everywhere. Very low output. After a thorough cleaning and recap it played like new.
Cheers,
AlbertAttached Files -
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There are RTV silicone (likely hot-glue, as well) products that are specifically made for electrical/electronics applications. They're made for very low electrical conductivity, and it's a good bet that if it was "dosed" at the factory, it was with this type.
Dow Corning has specs on their RTV silicone. Here's more than you ever wanted to know: http://www1.dowcorning.com/DataFiles...c8801fc0b5.pdfLast edited by Dave Curtis, dB AudioTech; 08-22-2009, 04:25 PM.Comment
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both instances described a cap replacement too, so maybe the RTV (non catalytic) silicone it trashing the caps? Most RTV cures by evaporation of the acetic acid, which could mess with electrodes within the caps. The common acetic acid (acetoxy) cure RTV is not used in electronics, but the alcohol (alkoxy) cure RTV is designed for this. Cured silicone does NOT conduct ever, as it is the insulation of choice for HV corona prone signals.Comment
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that's really good to know guys. Stay away from the glue that cures with acetic acid! Now, does anyone know where I can get clear glue with the alcohol vs the acetic acid? Looks like Permatex black will work, but I need clear. Thanks!Comment
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Momentive (formerly GE) 6708 might do the trick, Mcmaster.com has 10oz catridges:Originally posted by booj View Post
cat # 7547A583 $9.65 Each
(I like hot melt glues)Comment
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In both cases, There's really no way to know because more work was done than just removing the goop. I highly suspect that both amps would have had the same problems WITHOUT the goop, and a cleaning/recap was the actual fix. The Silicone I use doesn't even conduct before curing (reads OL on my meter, which goes up to 20 meg.)Originally posted by Albert Kreuzer View PostComment
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I didn't re-cap the amp. Just removed the leads from the mounting holes temporarily on the side going to the power tuibes. I could have been the connection, but the old connections didn't look bad though.Comment
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Personally, we use hot glue for these purposes. It is PVC-based and non-conductive even when in the liquid state. Unless you are right on the tube sockets in an inverted-tube amp (e.g. Fender, with the tube heat rising into the sockets) or on power resistors, it will not melt of soften, so there is no worries about that. In addition, it is easily removed by hitting it with freeze spray. Then, it cracks like glass and comes off cleanly.Comment
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I can tell you that GE Silicone I and II both cure with acetic acid, and I'm fairly sure DAP silicone products do as well - so mark those off the list of possibilities.-MikeComment
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...just for the record. I have removed glue from the tops of caps without doing anything else in a high-gain amp and it solved a feedback problem. The section was much less noisy after removing the glue.Comment
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RTV will make a huge mess of things. It eats solder joints.
JerryComment
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the red color in the sicone is made or iron oxide conductive, black permatex may use a conductive carbon blackComment
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It does....its right on the MSDS.Originally posted by t bake View PostThe farmer takes a wife, the barber takes a pole....Comment
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Agree. My lovely wife's craft hot glue gun has been permanently reassigned to duty in my shop. It's good stuff. I used red RTV in the aircraft repair business but only where it was specifically called out.Originally posted by jrfrond View Post
Some guys (like the cat who put those orange drops in) seemed to follow the Heinemann Rule-if twice as much is twice as good, five times as much is five times as good. They just love globbing the stuff all over.....come to think of it the schematic for my Crate TV56212 came with a "goop diagram" which is exactly what it says it is. On closer inspection it was put around all the electrolytics-all radial leads-I guess to keep them from bouncing around and getting loose.
On the other hand, self sealing silicone rubber triangle tape is a wonderful product if you have a use for it. I have a couple rolls of the stuff left over from doing service mods on bleed air switching valves. You wrap the stuff around whatever you like, and it bonds to itself like magic. It makes great insulation installations.Comment
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