Hello All,
Now that I have it all working I hear varous buzzes from the speaker cone vibrating against things. I can't see anything wrong. Should I remove all the screws from around the edge and try to center the cone better? Yes, I'll loosen the screw in the center as well to allow it to move. If I pull a tiny bit on one of the voice coil wires it helps at low volume. This is what tells me that the voice coil isn't centered in the gap. But maybe the entire cone is so dried out and brittle that it cannot flex as much as it once did. It is 75 years old. Maybe it can never sound as good as it once did.

Thanks,

Dave

Centering is a good idea. Use slits of film or index card between the coil and the pole piece. Check to be sure that the coil wires (flex wires that go from coil to terminals) aren't bumping against anything.

You can strengthen the main part of the cone if it is brittle by painting it with a thin layer of Elmer's glue thinned by water. It must soak into the paper, not sit on top. DO NOT get glue into the flexible outer edge. Don't over-do the glue, either. An explanation as to why you shouldn't will follow below.

With the outer edge, dampen with water, and then rub gently with vegetable oil, possibly mixed with a small amount of degergent to make it compatible with water, though I haven't tried this yet. I have had luck with just putting it onto the wet outer edge, though. I have found that applying oil to a dry edge doesn't work as well as applying it to a wet edge. I'm not sure why, since oil and water aren't compatible. The paper is water based, though, and needs water to soften it. Oil won't soften it, but will keep it soft once the water has done its work. You might also try a good grade of hand lotion, since it is made for softening skin, which is more water than oil soluble. Lotion has a magic way of softening the skin right away with the water based stuff, and then it keeps the skin soft with the oils and waxes.

I have had incredible jukebox-like results with oiling the outer edge of speaker cones. The tone quality is rich and wonderful. The only thing that works better is a cone from www.electronix.com. These don't always fit, and sometimes it's nice to keep a speaker original, though, so try working with the original cone first. Don't oil the main section of the cone. It's designed to move as a unit. If it flexes, waves will be set up along it. If you want it to push the air in a uniform manner for any given frequency, and not all of it is moving in the same direction, harmonics will be set up, and the speaker won't be as efficient. An extreme example of this is a wet cone or a rubber cone. Neither works very well, especially at high frequencies. While you want the cone to be stiff (except for the outer edge), you don't want it to be heavy, or else it will not respond well to high frequencies, which also will set up harmonics, as well as a taper off at high frequencies. Some speaker color is interesting, and is what makes old radios kind of cool (cabinet color adds to this), but you don't want to do drastic things to the cone. Don't put gobs of glue on it.

Thomas

Thomas,
How do I get the slits of index card between the coil and pole piece? The spider is a flat disc. I can't put the cards through that way.
I cleaned the tone control and checked its resistance but it has drifted to 100K from 50K. There doesn't seem to be any breaks in it. When I connect it to my ohm meter, I can turn it from zero to 100K. When I reconnect it, it works but it distorts the sound. It kind of sounds like the sound is breaking up. When it's disconnected, the sound is fine. I'm going to have to replace that control. Unless someting else is wrong but I don't see anything wrong.
Anyway back to the speaker. I have never put water or oil on a surround or on a speaker cone for that matter.. Usually I put rubber cement on it (the surround). But it seems like a good idea.

Thanks,

Dave
:Centering is a good idea. Use slits of film or index card between the coil and the pole piece. Check to be sure that the coil wires (flex wires that go from coil to terminals) aren't bumping against anything.
:
:You can strengthen the main part of the cone if it is brittle by painting it with a thin layer of Elmer's glue thinned by water. It must soak into the paper, not sit on top. DO NOT get glue into the flexible outer edge. Don't over-do the glue, either. An explanation as to why you shouldn't will follow below.
:
:With the outer edge, dampen with water, and then rub gently with vegetable oil, possibly mixed with a small amount of degergent to make it compatible with water, though I haven't tried this yet. I have had luck with just putting it onto the wet outer edge, though. I have found that applying oil to a dry edge doesn't work as well as applying it to a wet edge. I'm not sure why, since oil and water aren't compatible. The paper is water based, though, and needs water to soften it. Oil won't soften it, but will keep it soft once the water has done its work. You might also try a good grade of hand lotion, since it is made for softening skin, which is more water than oil soluble. Lotion has a magic way of softening the skin right away with the water based stuff, and then it keeps the skin soft with the oils and waxes.
:
:I have had incredible jukebox-like results with oiling the outer edge of speaker cones. The tone quality is rich and wonderful. The only thing that works better is a cone from www.electronix.com. These don't always fit, and sometimes it's nice to keep a speaker original, though, so try working with the original cone first. Don't oil the main section of the cone. It's designed to move as a unit. If it flexes, waves will be set up along it. If you want it to push the air in a uniform manner for any given frequency, and not all of it is moving in the same direction, harmonics will be set up, and the speaker won't be as efficient. An extreme example of this is a wet cone or a rubber cone. Neither works very well, especially at high frequencies. While you want the cone to be stiff (except for the outer edge), you don't want it to be heavy, or else it will not respond well to high frequencies, which also will set up harmonics, as well as a taper off at high frequencies. Some speaker color is interesting, and is what makes old radios kind of cool (cabinet color adds to this), but you don't want to do drastic things to the cone. Don't put gobs of glue on it.
:
:
:
:Thomas

Try shimming on the outside of the voice coil. I don't like the idea, but I've seen it done before.

As per the other thread, I think that you should try other condensers in the tone circuit. I don't think that the tone control is causing your trouble. I think that your condenser is causing the trouble, even though it's new. Try other kinds of the same value, rated for at least 400 volts. Then try some at .005 to .002 MFD.

The set originally worked with a .025 MFD condenser when new, but I don't really like that value. It seems too high for a grid circuit. It's more appropriate for the output circuit. However, depending on the impedances of those interstage transformers, higher capacitor values may be necessary.

T.

Dave

If the speaker is rubbing you should be able to feel it by lightly pushing on the cone. Sometimes adding cotton between the frame and back of the cone will fix this problem.

Be sure the edge of the cone isn't lose where it attaches to the frame. This isn't always noticed.

Norm

:Try shimming on the outside of the voice coil. I don't like the idea, but I've seen it done before.
:
:As per the other thread, I think that you should try other condensers in the tone circuit. I don't think that the tone control is causing your trouble. I think that your condenser is causing the trouble, even though it's new. Try other kinds of the same value, rated for at least 400 volts. Then try some at .005 to .002 MFD.
:
:The set originally worked with a .025 MFD condenser when new, but I don't really like that value. It seems too high for a grid circuit. It's more appropriate for the output circuit. However, depending on the impedances of those interstage transformers, higher capacitor values may be necessary.
:
:T.

You can also shim it and then wet the cone. Let it dry and it'll dry in the proper position.

T.