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What's the trick for soldering to a metal chassis?

6/21/1998 2:50 AM
Benjamin Fargen
What's the trick for soldering to a metal chassis?
On old amps, all of the grounded points on the terminal strips are soldered to the metal chassis. When I try to do this, the solder just balls up and never makes a nice solid connection, What's the trick?  
Thanks, Benjamin.
6/21/1998 9:00 AM
Paul Markwalter

For the solder to flow correctly, the point on the chassis needs to be clean, clean, clean and roughed with a grinding wheel, sandpaper or whatever. Then you need enough heat on the chassis to melt the solder and let it flow. A 200/260 watt gun does the job fine for us. Hopefully you are using fine, rosin core solder. Good luck
6/21/1998 10:25 AM

Ditto on the high wattage iron. If you think of the chassis' job, it not only holds the components, but dissipates heat. If you are trying to solder with a 35 watt iron, the minute it touches the chassis, the heat sinks out if it. That is why it is good for pc boards and delicate components like caps transistors etc. Get a 200+ watt Weller iron for chassis work. Mark
6/21/1998 1:20 PM

In addition to all the rest everyone has presented, I'd like to add that you may use a chemical cleaner on the chassis. Something like denatured alchohol or acetone (be careful of paint and plastic) do a good job of getting the grunge off.
6/21/1998 3:04 PM
Steve A.

    After cleaning the metal you can use a sharp tool to lay down a series of cross hatches for the solder to bond to.(I used to use various fluxes and after a few years the metal would be all corroded! Especially on pots where all I had to do was scrape off the coating. It is said that we learn from our mistakes so I must have a few PhD's by now!)  
    However, you need to ask yourself if you really want to solder the lead to the chassis- whenever feasible I think it's a LOT better to solder the wire to a hi-temp ring terminal and then secure the ring terminals to the chassis with a screw, nut and lock washer. You can usually find an existing screw hole to use if you don't want to drill on a vintage amp chassis. (Be sure to clean the chassis around the screw so it makes a good electrical connection.)  
Steve Ahola
6/21/1998 8:53 PM
I have at times used a little butane torch I got from Radio Shack. I will use a shield to keep from toasting fragile things, but it will make a real nice blob, sometimes you can't tell them from the original. Also go with the clean and scrape. Good luck.  
6/21/1998 9:59 PM

I think the previous posts covered the subject pretty well. The only thing I would add is that some materials are very difficult to solder to---aluminum comes to mind. Because of the native oxide that forms on it you'll find it almost impossible to solder to.  
The other thing to keep in mind is what Steve said earlier "Do you really want to solder all those connections to ground?". Certainly if you are making a bunch of ground connections to the chassis at different points you are asking for "ground noise hell". Believe me, you don't want all those different ground points.  

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