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Old 30th Jun 2019, 8:39 am   #21
stevehertz
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Default Re: Bush DAC 90 Asbestos Problem

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But you would need prolonged exposure to asbestos fibres, usually over many years, before you develop asbestosis.
Is that an actual fact? My understanding is that you only need to inhale a single fibre to be at risk? Obviously that's less of a risk than inhaling fibres over many years, but still a risk nonetheless.
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Old 30th Jun 2019, 10:25 am   #22
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Default Re: Bush DAC 90 Asbestos Problem

You need considerable exposure to get asbestosis which is similar to silicosis.
You only need one fibril to get mesothelioma which killed a friend on mine recently. It depends on whether the fibril gets inside a DNA helix.
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Old 30th Jun 2019, 10:37 am   #23
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Default Re: Bush DAC 90 Asbestos Problem

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Is that an actual fact? My understanding is that you only need to inhale a single fibre to be at risk?
If that were the case then everyone in the civilised world must be at risk. It's a fairly certain bet that almost everyone will have come into contact with it at some point in their lives.

To put it into context would smoking a single cigarette in someone's lifetime put them at greater risk of developing lung cancer? Theoretically, maybe but realistically probably not. Smoking 20 a day every day of course would be a completely different matter.

Yes, asbestos is a health hazard and should be treated accordingly but it isn't anthrax and a common sense approach to dealing with small amounts of it is appropriate.
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Old 30th Jun 2019, 11:19 am   #24
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Default Re: Bush DAC 90 Asbestos Problem

Just a note I worked for 50 years as an Electrician
I think you will find asbestos was every where In fuse carriers
Imersion heater connections spacers between circuits and of course cable
I worked on them all
If there may be a danger What about remove the rest of the parts for spares
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Old 30th Jun 2019, 12:12 pm   #25
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Default Re: Bush DAC 90 Asbestos Problem

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Originally Posted by stevehertz View Post
Is that an actual fact? My understanding is that you only need to inhale a single fibre to be at risk?
If that were the case then everyone in the civilised world must be at risk. It's a fairly certain bet that almost everyone will have come into contact with it at some point in their lives.

To put it into context would smoking a single cigarette in someone's lifetime put them at greater risk of developing lung cancer? Theoretically, maybe but realistically probably not. Smoking 20 a day every day of course would be a completely different matter.

Yes, asbestos is a health hazard and should be treated accordingly but it isn't anthrax and a common sense approach to dealing with small amounts of it is appropriate.
Puffing one cigarette is not a parallel with breathing in one fibre of asbestos. I think we're likely to have a few hundred views on this. My one view is to take a 'middle line'. I would treat the asbestos in one of the better ways suggested and proceed with the restoration. That's my own view, it's up to the individual. Asbestos clearly isn't the instant killer that arsenic is, but it has to be taken seriously no matter what the amount. It's all very well people saying that they worked with it for 40 years and have suffered no ill effects (yet), the dangers are proven and asbestos, no matter how small the quantity, has to be respected as a dangerous substance.
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Old 30th Jun 2019, 1:30 pm   #26
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Default Re: Bush DAC 90 Asbestos Problem

We've stumbled on the distinction/s between Mesothelioma, Asbestosis, Asbestos related pleural disease, etc. As discussed previously there are distinct types of fibre with different risk factors, and lab. testing sets you back £100 straight away, so the default position is to treat anything that looks like it might be loaded, as requiring special attention.
I too had rejected PVA as a solution for droppers since data sheets say it can decompose with heat. I don't know what makes step & sill repair cement different from other cements, but in the absence of any purpose made sealers it has to be worth looking into..

Official asbestos warning stickers are available cheaply, and can be put somewhere inside the equipment where they'll be obvious to anyone in future.

No need to throw the radio out in my opinion, that would just be moving the issue elsewhere. Stabilising the material is the way to go. If it's ridiculously friable (now there's a word) that's when you have to think about proper damping down for removal on a wind free day, double bagging and official disposal (which tends to be FOC for small amounts) Hopefully it won't come to that.

In any case any old radio under threat of disposal for 'safety reasons' will generally find a new home on here..

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Old 30th Jun 2019, 1:45 pm   #27
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Default Re: Bush DAC 90 Asbestos Problem

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But you would need prolonged exposure to asbestos fibres, usually over many years, before you develop asbestosis.
Is that an actual fact? My understanding is that you only need to inhale a single fibre to be at risk? Obviously that's less of a risk than inhaling fibres over many years, but still a risk nonetheless.
I've no idea, I never said it was or wasn't I'm not medically trainied and no expert on such matters so I'll bow to those who are, I just quoted the NHS for which I provided the resource reference.

John
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Old 30th Jun 2019, 1:58 pm   #28
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Default Re: Bush DAC 90 Asbestos Problem

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I don't know what makes step & sill repair cement different from other cements, but in the absence of any purpose made sealers it has to be worth looking into..
I don't know either, except it works, sets quickly, doesn't crumble, no sand needed. it's a very liquid paste (so needs clamped on battens for a step or sill) and it comes in a box like pollyfilla. It's not cheap. I'd say you'd want to rebag it and keep in the freezer (very dry place, perfect for ground coffee too) till needed for something else.

*

I've a DAC90 to restore. I'll be putting clear parcel tape over outside of missing piece of case reinforced with duck tape and filling with "David's Isopon" or similar polyester filler from the inside. This produces a perfect outside finish I'll colour afterwards, though there are powder colourants for resins.
Then I'll have to make a back. Traditionally people have used hardboard or MDF (easier to rout or drill). The dust from those isn't good! I'm going to try multiple layers of cereal box card, cut/punched (maybe an oval punch made from a steel pipe sharpened and then squashed), stained and then PVA glued and clamped. Perhaps the top layer colour laser printed paper.
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Old 30th Jun 2019, 2:46 pm   #29
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Default Re: Bush DAC 90 Asbestos Problem

I would get rid of the asbestos, Masterboard (amongst others) of a suitable thickness would be a good sub, sometimes friendly builders or plumbers have offcuts for free.

Lawrence.
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Old 30th Jun 2019, 2:59 pm   #30
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Default Re: Bush DAC 90 Asbestos Problem

Lots of people worked with asbestos, sawed it, breathed in the fibres, and had no ill effects. Car brakes must have generated lots, cleaning out brake dust from brake drums was just a fact of life. Chances of health problems from a DAC90 dropper is minuscule.

Having said that, for the few who were susceptible, asbestosis was a horrid thing to suffer from. By the time you know you are susceptible, it's too late.

I think the advice above is all realistic. (My own DAC90 has an undisturbed dropper, and if I ever do need to disturb it, I'll be wearing a face mask and doing it outside. "The solution to pollution is dilution"). Asbestos is after all, naturally occurring in Nature.
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Old 30th Jun 2019, 4:27 pm   #31
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Default Re: Bush DAC 90 Asbestos Problem

I would get rid of it, outside and soaked in water. I have used weak wallpaper adhesive in the past but only because I had some leftover.
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Old 30th Jun 2019, 5:14 pm   #32
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Default Re: Bush DAC 90 Asbestos Problem

I'm not familiar with the DAC 90 but my 90A doesn't have a shroud and therefore there is no asbestos either. It seems to me that the 90's arrangement has a tendency to concentrate the dropper's heat in a rather undesirable way so would it be possible to remove the shroud completely with the asbestos still inside? If this could be done without significantly disturbing the asbestos this might be a way forward. Even rivets could be carefully drilled by a masked individual after wetting the asbestos with water, dilute PVA, wallpaper paste or whatever. The whole lot could then be bagged and disposed of safely. A piece of aluminium sheet fixed above the dropper might be needed to add a little heat protection for the case and back. Perhaps someone has tried this in the past and can comment accordingly?

Alan
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Old 30th Jun 2019, 6:06 pm   #33
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Default Re: Bush DAC 90 Asbestos Problem

I have a theory about the DAC90 asbestos, feel free to shoot it down if you disagree!

I think it might have been a precaution to protect the light coloured Urea Formaldehyde cabinets from discolouration, the Bakelite ones possibly didn't need it.

I removed the asbestos from mine, first I very carefully, without disturbing the asbestos, removed the small nuts bolts and washers securing the dropper and put it to one side. Then I dampened the asbestos with a water spray using a plastic bag to catch the excess water. then I unbolted the dropper carrier and placed it in a sink-full of water where I could scrape out the asbestos in complete safety.

I didn't attempt to replace the asbestos with a substitute, I have heard of ceramic tiles being used but surely that's a good conductor of heat (cold to the touch) and therefore not suitable, NASA Shuttle tiles excepted of course.
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Old 30th Jun 2019, 7:14 pm   #34
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Default Re: Bush DAC 90 Asbestos Problem

Graham's approach sounds very sensible especially as the shroud is bolted rather than riveted in place. However, I still wonder why manufacturers thought it was a good idea to enclose dropper resistors in this way? Surely the dropper is more likely to overheat when not exposed to free airflow and, in the case of the DAC90, long term damage to the back becomes almost inevitable?

Alan
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Old 30th Jun 2019, 9:59 pm   #35
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Default Re: Bush DAC 90 Asbestos Problem

Hello all thanks for your advice
I Have now have a plan for your consideration

All work to be done outside (Using surgical gloves)
1) Remove chasis from case
2) Cut off the cables and remove the dropper (Put in bucket of water)
3) carefully paint the asbestos with diluted pva glue (Leave for 4 hours)
4)Unbolt the frame and drop into a bucket of water(Then later I can remove the asbestos) Prefer though to make some sort of a new frame
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Old 30th Jun 2019, 10:25 pm   #36
60 oldjohn
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Default Re: Bush DAC 90 Asbestos Problem

Once safely removed, I would dispose of the whole dropper. I safely use a DAC90 daily. Some years ago I bought an Auto transformer from Ed Dinning, fitting this to the holes already in the chassis. This converts the set into an AC90, the instructions are at the end of the manufacturers service sheets. This also does away with the problem of sourcing dial bulbs, there is a 6.3v tapping. This TX also fits the DAC90A using different tapings. Another bonus there is no heat to burn the card back of the set. Please be aware the set will still be a Live Chassis set.


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Old 1st Jul 2019, 12:47 pm   #37
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Default Re: Bush DAC 90 Asbestos Problem

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I still wonder why manufacturers thought it was a good idea to enclose dropper resistors in this way? Surely the dropper is more likely to overheat when not exposed to free airflow and, in the case of the DAC90, long term damage to the back becomes almost inevitable?
Good question. The asbestos sheet in the DAC90 looks like an after-thought possibly due to the metal frame conducting the heat onto the chassis and cabinet. A deflector plate with a corresponding slot in the back panel would be the logical solution to venting heat from the dropper. I guess the live chassis prevented using a metal plate but there are non-conductive materials available these days.
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Old 1st Jul 2019, 9:56 pm   #38
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Default Re: Bush DAC 90 Asbestos Problem

Hi.

I was wondering if anyone has tried using a capacitive dropper in the DAC 90?

Regards,
Symon
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Old 2nd Jul 2019, 10:40 am   #39
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Default Re: Bush DAC 90 Asbestos Problem

No reason why not. You'll need to remove the dropper, add 2.84uF of suitable capacitors in series with the heater chain and increase the value of the series resistor to the rectifier anode to drop the HT back to where it should be. The series resistor for the rectifier should connect to the mains side of the dropper capacitor.
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Old 2nd Jul 2019, 10:50 pm   #40
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Default Re: Bush DAC 90 Asbestos Problem

That's good advice Chris. It certainlly makes a lot of sense carrying out this mod to reduce the heat dissipation in the set and also gets rid of the asbestos problem.

Regards,
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