The Steel Guitar Forum

The tone & volume pots on my old National 6 string were making noise, so I squirted a little WD-40 in the pots. They move easier & make no more noise. I should say that they make no noise when they are adjusted and no string is being played. When I strum any strings and adjust the tone all the way counter clockwise, it makes a pop. Is the .05 MFD capacitor bad? Why is the cap so big (it is a little bigger than a firecracker), while the cap in my other guitars is realy small?

Steve,

In the days when that National was made, caps were all made of foil and waxed paper separating the two "plates". This made them large. As the years went by, designers begain using other materials. The most notable ways mylar and ceramic.

And along with this they became increasingly smaller in physical size. So you can replace that cap with the same value and it will be much smaller and yet be an exact duplicate of what you have in there.

One word. Spraying bad pots is usually a short-lived situation. After a while the carbon coating that the "wiper" slides on gets soooo thin it develops holes in it.

The best thing is to simply replace them.

God bless you in your quests,

carl

Steve, the pop at the end of the tone control is because the pot is bad. Either the resistance element is worn at the end, or the internal stop in the pot is bent enough (or worn) to allow the slider to go off the resistance element and on to the rivet which secures it.
The remedy is, of course, to replace the pot.
The .05 mfd cap is big because it is old technology. In the '30's and '40's the caps were made of alternating layers of foil and wax paper. If you can read the voltage rating it will be either 200,400,or 600 volts, D.C.
You don't need that voltage rating but that's what was available.
Most guitars I've seen of that vintage used a .05 mfd, 200 volt cap.
The new technologies use mylar or polyester film with a metallic coating. Much smaller for the same voltage rating.
You can also get lower voltage rated caps which are even smaller.
Over the years, the old caps gradually develop leakage which impairs their
performance. The capacity may change enough so that the range of the tone control is affected. If you replace the pot, you might as well replace the cap as well.
If you want to retain the vintage look of the electronics, it is an easy matter to melt the wax on the old cap, push out the old
insides and mount the new cap inside the old one. I do that on vintage radios. If you decide to do that, E Mail me and I will give you the details.

Blake