July 2, 2024

Myth Dispelling Time

I’ve seen one too many posts about silver tarnish being conductive. One of the things I do on every SHP amplifier redo is desolder the tone controls, take them apart and clean the contacts by hand. I have learned this the hard way. Too many times I have douched them down while actuating the slide controls furiously to try and clean them. I really thought I was accomplishing something. Measuring after cleaning it was apparent not much was happening with the “drown” method. The method of desoldering and disassembly is a very positive way to make sure they are clean. 100% accuracy.

Try your slide controls for the bass and treble. Hear any difference when you switch them from setting to setting? If not then they are dirty. The first time I cleaned them this way I was very surprised when I heard distinct changes in tone when switching either one; treble or bass. That is all I needed to be convinced. These amps actually have quite good tone when given a chance. Since the SHP series amplifiers are 40+ years old they need all the help we can give them.

Back to the silver tarnish. Too many people repeat what they hear or read having no practical knowledge of the subject. The contacts on the tone controls are silver plated and tarnish like any other silver does slowly turning black. I’ve seen one too many posts on a favorite Facebook page that states silver tarnish is conductive. Nonsense! In the first picture I show one side of the slide control, the middle, connected to an ohmmeter. You can see it measures almost a 1,000,000 ohms-a lot of resistance. It should read less than 1 ohm resistance.

Here is a picture of the disassembled tone control. Note the build up of tarnish.

A short discourse…..Desoldering these is just like removing any other component on a circuit board. Once removed I used a small pair of dikes or diagonal cutters to pry the two legs away from the slide lever holding the unit together. These contacts can be then cleaned by a variety of methods. Use a soft wire brush, a fiberglass eraser, a big “Pink Pet” pencil eraser, a cotton swab dowsed in your favorite cleaner. Put the two halves back together, bend the two legs back. Look at the other two unbent legs as a guide as to how far to bend them back. Not enough and the tone control will come apart. Too far and the little board gets pushed out of place.

Here is a picture of the same contact measurement after cleaning. You can see quite a difference. With practically zero resistance you will get very distinct differences when switching the tone controls and can have an amp much more “tune-able” as to how you like your music to sound. And it’s easy to see that the silver tarnish caused quite a resistance.