My Yamahas have had a hard life. Getting married and kids relegated them to the garage for a few years, then into the workshop where the angle grinder gets used quite a lot. As part of my recent workshop upgrade, I thought I would upgrade my sound system and the Yamahas didn't sound like I remembered. Inspection revealed one tweeter was dead, and one mid was distorting badly.
A friend pointed me at this
which is an encouraging demo of a simple fix to the tweeter.
I didn't really have anything to lose so I thought I would try what I previously thought impossible - fix the drive units.
My tweeter was in a much worse condition than the youtube vid. The Copper Clad Aluminum ribbon had corroded for about 1/3 of a turn (turned to white aluminium oxide powder) which meant nothing to solder on to, and the coil had become detached for that area.
Nothing to lose now! so I unpicked the epoxy hoding the coil on This shows the state of the coil and dome just after freeing the coil:
During clean-up I broke the negative tail of the coil as well 🙁.
Next challenge is to get something to solder on to. I unwound a bit of the negative tail, and unwound almost a full turn of the positive tail. CCA is incredibly fragile and this is probably the most challenging part. I used magnification, a scalpel, time, and a lot of tea breaks. That left me with a long positive tail, and just enough on the negative to lay flat across the coil and solder an extension. Note these Yamahas use a single layer coil so the negative is glued flat across the coil to get it back to the bottom of the coil. the smallest drop of superglue stuck it back to the coil. Here we are with long tails:
I was very wary about soldering the CCA so stopped as soon as I had electrical contact. This does not look nice!
The coil is now out of round 🙁
Coincidentally, a cigar tube happened to be just the right diameter, so I put the coil on this and placed on the cleaned-up dome (I picked off all the old glue with a scalpel and lots of tea again).
I spend a while getting this centred by eye. Then I tacked in place with small dots of superglue.
Ease out the cigar-tube coil former and tack with superglue on the inside:
Then solder it up. I broke the negative tail again so had another go at soldering - what a mess! I'm using a bit of transformer winding for the extension.
Super glue the tails in troughs cut out in the surround. Then glue all around inside and out with thinned 2 part epoxy:
Carefully screw it back together. OMG! It only flipping works!
It sounds perfect to me - but I'm old (I've had these Yamahas for over 35 years).
I wonder if that incredible beryllium dome midrange can be bought back to life?! .... watch this space.
A friend pointed me at this
I didn't really have anything to lose so I thought I would try what I previously thought impossible - fix the drive units.
My tweeter was in a much worse condition than the youtube vid. The Copper Clad Aluminum ribbon had corroded for about 1/3 of a turn (turned to white aluminium oxide powder) which meant nothing to solder on to, and the coil had become detached for that area.
Nothing to lose now! so I unpicked the epoxy hoding the coil on This shows the state of the coil and dome just after freeing the coil:
During clean-up I broke the negative tail of the coil as well 🙁.
Next challenge is to get something to solder on to. I unwound a bit of the negative tail, and unwound almost a full turn of the positive tail. CCA is incredibly fragile and this is probably the most challenging part. I used magnification, a scalpel, time, and a lot of tea breaks. That left me with a long positive tail, and just enough on the negative to lay flat across the coil and solder an extension. Note these Yamahas use a single layer coil so the negative is glued flat across the coil to get it back to the bottom of the coil. the smallest drop of superglue stuck it back to the coil. Here we are with long tails:
I was very wary about soldering the CCA so stopped as soon as I had electrical contact. This does not look nice!
The coil is now out of round 🙁
Coincidentally, a cigar tube happened to be just the right diameter, so I put the coil on this and placed on the cleaned-up dome (I picked off all the old glue with a scalpel and lots of tea again).
I spend a while getting this centred by eye. Then I tacked in place with small dots of superglue.
Ease out the cigar-tube coil former and tack with superglue on the inside:
Then solder it up. I broke the negative tail again so had another go at soldering - what a mess! I'm using a bit of transformer winding for the extension.
Super glue the tails in troughs cut out in the surround. Then glue all around inside and out with thinned 2 part epoxy:
Carefully screw it back together. OMG! It only flipping works!
It sounds perfect to me - but I'm old (I've had these Yamahas for over 35 years).
I wonder if that incredible beryllium dome midrange can be bought back to life?! .... watch this space.
To complete the story... To give you and idea of the condition of the mids, This is a closeup after taking one out the cabinet:
A lot of that is iron filings - impractical to clean off while there is a big magnet attached.
Also note white powdery corrosion on the beryllium.
There are some larger bits of metal as well... I was hoping just a clean might solve the problem:
After separating the magnet, and cleaning off the swarf, it became clear the suspension had come away from the dome for about 1/4 of the diameter. See the break in this pic?
Here is the good side still attached:
Again. I tacked it shut with superglue then used the thinned epoxy
and expxied all around the outside as well.
The result is that this one now sounds better than the other. No distortion.
I'm sure if you measured the performance of these repaired drivers to brand new ones then you could probably tell a difference, but in my listening setting, these really bring back some life to the old speakers.
A lot of that is iron filings - impractical to clean off while there is a big magnet attached.
Also note white powdery corrosion on the beryllium.
There are some larger bits of metal as well... I was hoping just a clean might solve the problem:
After separating the magnet, and cleaning off the swarf, it became clear the suspension had come away from the dome for about 1/4 of the diameter. See the break in this pic?
Here is the good side still attached:
Again. I tacked it shut with superglue then used the thinned epoxy
and expxied all around the outside as well.
The result is that this one now sounds better than the other. No distortion.
I'm sure if you measured the performance of these repaired drivers to brand new ones then you could probably tell a difference, but in my listening setting, these really bring back some life to the old speakers.
I would agree that breathing beryllium, particularly beryllium oxide, is a bad idea. I think the risk of serious illness can be managed without having to do this outdoors but by all means, do it outside if you want to. In general, it is a bad idea breathing any dust, let alone beryllium.
The pure beryllium domes are quite stable. The epoxy comes off them quite easily in chips - you don't have to scrape away the metal.
The white spots on the dome could well be beryllium oxide. It does not come off easily. I would suggest cleaning with alcohol soaked cotton buds and vacuum. I would not suggest scraping off the corrosion and blowing or using compressed air to clean the domes.
I read a few things on the internet saying these are difficult to fix - things about high tolerance, difficult to get apart etc. I didn't encounter any such difficulties.
The pure beryllium domes are quite stable. The epoxy comes off them quite easily in chips - you don't have to scrape away the metal.
The white spots on the dome could well be beryllium oxide. It does not come off easily. I would suggest cleaning with alcohol soaked cotton buds and vacuum. I would not suggest scraping off the corrosion and blowing or using compressed air to clean the domes.
I read a few things on the internet saying these are difficult to fix - things about high tolerance, difficult to get apart etc. I didn't encounter any such difficulties.
I don't think oxidation of beryllium is normally much of an issue. These speakers are 40 years old (at least) and been in a very harsh environment. However, the choice of Beryllium is extreme - it was very tricky to get hold of and form back when these speakers were designed - -vapour disposition! Any smear of shellac would have been seen as compromising the design.
So I'm not tempted to do anything to stop further corrosion other than clean them. The mass of iron filings and whatever else is in dust probably significantly contributed to the conditions needed for the corrosion.
In my search for info on fixing these drivers I happened across a youtube vid of a factory tour of focal (I have focal shape twin in the house currently which are much more 'acceptable' (unobtrusive)). It includes assembly and discussion of beryllium tweeters so might be interesting (light, stiff, and inherent damping make it 'the best' material) - you also get a flavour of the special health and safety measures a reputable manufacturer has to go to when handling beryllium and showing members of the public around their factory (i.e. none). It is long, but I enjoyed it.
So I'm not tempted to do anything to stop further corrosion other than clean them. The mass of iron filings and whatever else is in dust probably significantly contributed to the conditions needed for the corrosion.
In my search for info on fixing these drivers I happened across a youtube vid of a factory tour of focal (I have focal shape twin in the house currently which are much more 'acceptable' (unobtrusive)). It includes assembly and discussion of beryllium tweeters so might be interesting (light, stiff, and inherent damping make it 'the best' material) - you also get a flavour of the special health and safety measures a reputable manufacturer has to go to when handling beryllium and showing members of the public around their factory (i.e. none). It is long, but I enjoyed it.
My other tweeter has now bust...
Reading about 70 ohms so not quite complete fail. Prodded around very gently and the coil wire disintegrated just where the end that comes from the top of the coil and across the windings is tacked onto the dome (and then is loose across the suspension). The solution is to unpick the wire where it comes across the coil and then unwind just enough to be able to get enough length to solder on a new bit of wire to make the connection.
Going really carefully with a 10x magnifier, watch screwdriver used as a scraper, and scalpel... and eventually you can get a scalpel under the wire to free it up. The Mid and tweeter I fixed above are still going!
Reading about 70 ohms so not quite complete fail. Prodded around very gently and the coil wire disintegrated just where the end that comes from the top of the coil and across the windings is tacked onto the dome (and then is loose across the suspension). The solution is to unpick the wire where it comes across the coil and then unwind just enough to be able to get enough length to solder on a new bit of wire to make the connection.
Going really carefully with a 10x magnifier, watch screwdriver used as a scraper, and scalpel... and eventually you can get a scalpel under the wire to free it up. The Mid and tweeter I fixed above are still going!