Salvaging coil rubbing green backs

[StingRay85]

Bought a quad of coil rubbers last week... and was somehow able to clean them reasonably well. All four of them rubbed quite hard, even though when I tested the cab with my bass, I only heard a clear coil rub in one of the four speakers. I still have more than ten of those coil rubbers on the shelf, and in the past my approach was to take small pieces of paper, and go into the coil gap to try to free up those particles. Not much luck there.

What I did this time was very carefully remove the dust caps, but using a tiny blade. Next it was clear that debris of the glue of the dust cap, and perhaps even sand particles were visible on the pole piece. I build a small setup with a solid state amp (my trusty Acoustic 220), and used a signal generator as the input for the amp, and output I made a jack socket with a lead that has two clips. Hook up the speaker, put it on two books with the sides, facing down, and make sure the air can escape. and then gradually increase power on a 20 Hz to 40 Hz signal. Shake the speaker around a few times, and repeat multiple times until no more rub. So far looks like a success.

Also noticed that my other coil rubbers where I gave up on where typically have brown residue in the coil gap. I always assumed this was corrosion, iron oxide, and the speaker was beyond repair, but it looks more like the glue that was used between spider and the basket is the cause of the particles. While in a good speaker it looks a big yellowish, in the bad one it's typically brown and easy to lift. Of course trying to repair only makes sense when the coil is still properly centered. But has anyone got any experience with carefully lifting the entire spider, clean up the mess, and re-glue the spider once the speaker is again clean from the inside?

Maybe also a good indicator for anyone that's in the market for buying pulsonic greenbacks. See what color the spider glue has. If its looking brown, then the life expectancy is lower than for a yellow one.

 

[BygoneTones]

But has anyone got any experience with carefully lifting the entire spider, clean up the mess, and re-glue the spider once the speaker is again clean from the inside?

Short answer is no. The way I used to do it (but don't any more) is remove the entire cone and clean it out properly that way. Then glue the old cone back in. I don't recommend doing that.

The last time I tried to repair a speaker the way you are describing, by just cleaning uner the spider and under the dust cap, I was still left with debris in the coil gap. It was better, but not a perfect speaker.

There's a guy in London that is going to give me some pointers on this, I still need to ring him.

I've got a T1221 quad from 66 I'm hoping to repair in that way, but only after I've spoke to the expert. I don't like taking the whole cone off, it can alter the tone of the speaker.

re coil rub, there can be numerous causes, it is not always just dirt and glue debris. not always repairable. The coil can be warped out of shape, or over heated - the laquer tends to bubble up, or maybe a loose wire. It can he hard to know exactly what the problem is without actually removing the cone then you can access the coil.

 

[Tatzmann]

I always fixed the rub with recentering, sometimes the fast and easy way, sometimes the longer, more correct way. Never had any debris in the gap.

 

[TomBallarino]

I always fixed the rub with recentering, sometimes the fast and easy way, sometimes the longer, more correct way. Never had any debris in the gap.

Could you give some pointers of what you mean with "recentering"? How do you accomplish that?

thanks
Tom

 

[racerxrated]

Could you give some pointers of what you mean with "recentering"? How do you accomplish that?

thanks
Tom

I read a couple articles/youtube vids on how to do this. The cliff notes response is, you have to carefully cut the dustcap off, but not at the base since you might hit the wires..then use a light vaccum to get any particles out, then use a shim of some type(cut a 3x5 card into strips, or use the whole card) and place the shim in between the cone and the coil. Then take acetone or rubbing alcohol and using a dropper put in on the spider all the way around, on the top. Then cover the open voice coil so nothing can get in, maybe a jar cap or similar. Let sit overnight. The next day when you remove the shims there should be equal spacing between the coil and cone, so no more rub. Carefully glue the dust cover back on.
IF this is not correct, anyone feel free to chime in....

 

[Blake F]

If it's truly just hardened glue debris (which is super common for 70's Celestions), you can often remove the dust cap and push the debris through to the area behind the former with thin mylar strips. Then you can loosen a couple inches of the spider and put a cotton ball in the gap to hold it open. The pieces can be shaken or blown into the spider area and out through the loosened gap. If you only loosen a couple inches of the spider, you won't have to re-center it and can simply re-glue it with Weldwood contact cement. Use Weldwood to re-attach the dust cover too.

However, rubs are often because the speaker coil was overheated by too much wattage and the former is deformed or is off-center. You need to carefully see what's going on with the dust cover removed. With a magnifying glass and bright flashlight you need to inspect whether the coil windings have had their enamel rubbed off and whether any debris is actually enamel from the winding. If the coil windings don't have bare spots you may be ok to try and re-seat a deformed former. To see if it's deformed, you need to take mylar sheets (probably stack a few of them for proper thickness) and see if the gap that the coil sits in is uniform- if it's deformed, the gap will be significantly different and may have the enamel rubbed off. You can try re-centering the coil, but you have to carefully remove the former/coil from the speaker cone which can be difficult. Best tool to separate the coil from the cone is a 'hot blade' which is a blade with a heat element you plug in that will melt the glue as you cut/separate. You can get mylar sheets at an office supply store but they'll only be one thickness (which you can stack). Mylar sheet of differing thicknesses are used in speaker kits to center the former when doing speaker repairs. If you want to re-center the coil, you may need a mylar kit of different thicknesses from a speaker repair supplier. While removing and re-centering a coil isn't the easiest thing in the world it's not super-difficult either. Just remember to get the coil re-centered well and exactly as deep on the cone as it originally was.

Better: If the coil just seems off-center it's probably easier to remove the glue on the spider's edges where it's glued onto the frame, and re-center the coil and spider assembly together, using a mylar kit from a speaker repair supplier, then re-glue the spider to the frame with Weldwood.

Tips: 1) to apply contact cement without a mess, I bought some dental syringes on eBay- they have a curved plastic tip. Snip it a bit bigger as the glue is thick. Then pull the glue into the syringe and you can apply it very professionally with the syringe. 2) to get the dust cap off, put a glue remover like Goo Gone or similar on a q-tip and apply sparingly just to one spot, wait 20 seconds and pry slightly with one tip of a tweezer (I prefer a scribe with a 90 degree bend but you have to be careful not to poke the cone)- watch carefully that it's separating without tearing the cone- if not, apply a little more and carefully wait for it to melt the glue. Repeat and proceed further around the cap as it loosens. Do not try to apply to the whole cap and pull it all off. Just go around, pry gently and loosen as the chemical melts the glue. Same for the spider if you need to remove it.

 

[StingRay85]

I only have one or two greenbacks with rub that originates from overheating. All others are just the glue and debris, have at least 10+ of those, and most of them I could fix using my method. The problem with pushing dirt through the coil gap, is that it gets stuck in the back, and only way out is through the other side of the coil gap, where you cannot reach it anymore.

 

[Blake F]

I only have one or two greenbacks with rub that originates from overheating. All others are just the glue and debris, have at least 10+ of those, and most of them I could fix using my method. The problem with pushing dirt through the coil gap, is that it gets stuck in the back, and only way out is through the other side of the coil gap, where you cannot reach it anymore.

Pretty simple process then to remove the dust caps, open the spiders slightly and get the glue debris out through the spider opening. Weldwood contact cement is almost identical to what they used back then to glue the entire speaker. After like 7 decades it's just finally getting brittle. Pretty amazing. And you will end up with some great-sounding speakers for bargain prices. Most people don't know you can do this. I've developed this method having done it to at least 6 vintage greenbacks. I realized you could get the debris out through a gap in the spider because I had several where the spider was coming off and there was glue rattling around. Pretty easy to fix but most people won't even attempt it.

 

[DirtySteve]

What does coil rubbing sound like? I've never heard of this so I'm just curious.

 

[racerxrated]

What does coil rubbing sound like? I've never heard of this so I'm just curious.

It's a slight scraping sound...you have to pull the speaker, or make sure it sits flat if you try it in the cab. Turn the speaker so it faces you, and gently push down on the cone. If it's touching the voice coil you'll hear that scraping sound. Bygone Tones has a good description of what to do on his website.

 

[StingRay85]

In many cases you only hear it on low frequencies. If you hit a cab hard with a bass on a low E and it produces a buzz or rattle, in many cases it coil rub (and sometimes indication of a lose spider).

 

[BygoneTones]

Depends on the speaker. Firstly there are numerous faults / issues that can cause coil rub, and secondly it can vary in severity. From barely noticable, to sounding bleeding awful. There are other issues besides coil rub that can make a speaker sound bad too.

Usually it's a buzzing / rattling noise, and you have to put some volume into the speaker before you can hear it. The cone has to move up and down before it will rub, and when you play quietly through a speaker the cone only vibrates a miscroscopic amount (so much so that it doesn't look like it's moving at all). That is one of the frustrating things about buying speakers online, people usually just do the battery test, multimeter test, or play music through the speaker quietly, and then write that the speaker "works perfect and sounds awesome" in their description.

Fwiw you do not usually need to cut through the dustcap on a vintage greenback. They will usually peel off fairly cleanly. It's the later speakers you might have to cut (G12-65's etc and later), as they used a much stronger glue on the dustcap late 70's onwards.