Bush DAC90 Asbestos Problem

[FStephenMasek]

Originally Posted by HamishBoxer

If it is ok (the dropper) I might be tempted to hold a vac near it to suck up any loose fibres and then leave it.

To replace it I would wet it carefully first outside before touching.

I am an asbestos expert and owner of an environmental consulting company. DO NOT use a household vacuum, as it will spread the fibers. It is best to leave it alone, unless the resistor is bad. Modern ceramic insulation might be a good substitute. Wetting asbestos with a mist of water with some soap added and wearing a proper tight-fitting respirator (not a paper mask!) and disposable gloves are appropriate when handling asbestos.

[HamishBoxer]

All noted Thank you.

[Spike47]

Hi

I have a Bush DAC90 , have just been told that it has "Blue Asbestos " surrounding the "large vertical resistor" , I did know that there was some form of asbestos surrounding it !.

My question is , could I suck it out , using a bagged hoover , or would that be detrimental to the heat produced by the capacitor to other components within the Radio ? .

Cheers
Spike

[TrevorG3VLF]

Blue asbestos is nastier than white asbestos,
Do not use a vacuum cleaner. You will spread the dangerous fibrils which pass through the filter.
A friend of mine has recently died from mesothelioma - not funny.

What capacitor? A decent capacitor in any role should not get hot.

[KeithG1XFL]

Hi
I have a DAC90 (NOT DAC90A) Which has a Asbestos Lined Box around the Mains Dropper Resistor which I in the Process of Restoring.

I would like to Remove the Asbestos, For Obvious Reasons, Does anyone have a any suggestions for What I could Use to replace the said Asbestos ?

Obviously it has to withstand a certain amount of heat, Can Anybody tell me approximately HOW hot it Get's under normal circumstances?

Thank You

Keith - G1XFL

[kalee20]

I'll measure mine this evening for you.

[KeithG1XFL]

Thanks Dale
That would be VERY much Appreciated



Regards
Keith

[Techman]

I've been warning about not using a 'domestic' vacuum cleaner to suck the dust out of vintage radio equipment, regardless of asbestos, for years. It can spread the tiny particles all around the house and contaminate everything for years to come. Any cleaning should always be done outside and preferably on a damp (but not wet as in raining) day.

[KeithG1XFL]

Sorry, I dont know where I got the Name Dale from, it must be some sort of mental thing.

Regards
Keith

[kalee20]

Just to say - I haven't forgotten the measurement, but I have forgotten to bring thermocouple meter home!

Maybe tomorrow...

[kalee20]

Here as promised!

After 1/2 hour of use, temperatures as follows, measured with a decent Fluke meter and thermocouple:

Dropper resistor aluminium housing: 84 deg C.

Air immediately above the dropper: 171 deg C (see photo).

The asbestos is certainly doing a good job with heat insulation! I dread to think what it would be with the back in place, close to a wall... not that many DAC90's have intact backs of course...

[G.Castle]

The primary functions of that paxolin tag strip seems to have been inverted during the life of your set Peter.

[KeithG1XFL]

Thanks for That.That gives me somethinig to work with anyway.
As another Noted, the paxolin strrip seems to be upside down (compared to mine anyway)


Anyway
Thanks Again

Keith

[kalee20]

Interesting! Can either of you post a photo of yours?

The Paxolin tag strip, with its terminals, does match the aluminium sentry-box enclosure which has mouse-hole cut-outs in its side, so the dropper plus strip can't go in the other way up.

I do intend to remake the strip in high-temperature laminate (silicone resin/glass-fibre composite) sometime, and rebuild this little radio 'properly' so I'd be interested in build variants!

[David G4EBT]

Originally Posted by KeithG1XFL

Hi
I have a DAC90 (NOT DAC90A) Which has a Asbestos Lined Box around the Mains Dropper Resistor which I in the Process of Restoring.

I would like to Remove the Asbestos, For Obvious Reasons, Does anyone have a any suggestions for What I could Use to replace the said Asbestos ?

Thank You

Keith - G1XFL

I don't have a DAC90A, but if I did, and wished to remove the asbestos and replace it, I'd probably re-purpose a plumbing/soldering/brazing heat shield mat, cut to size. EG: 'Silverline Heat Resistant Soldering Brazing Heavy Duty Plumbing Mat 300x250mm' (Good to 600C):

https://www.amazon.co.uk/Silverline-...5301253&sr=8-7

(300mm x 250mm, so one mat would be enough for several '90A asbestos replacements)

Hope that might help.

[David G4EBT]

Too late to correct the typo where I said ‘DAC90A’, when of course I was referring to the DAC90 which is the subject of the thread. (Really two appliances in one - a radio and a room heater - buy one, get one free ).

[G.Castle]

Originally Posted by kalee20

Interesting! Can either of you post a photo of yours?

The Paxolin tag strip, with its terminals, does match the aluminium sentry-box enclosure which has mouse-hole cut-outs in its side, so the dropper plus strip can't go in the other way up.

I do intend to remake the strip in high-temperature laminate (silicone resin/glass-fibre composite) sometime, and rebuild this little radio 'properly' so I'd be interested in build variants!

Looking carefully there is no difference in the way the sets are made, I just noted that the top of your sets dropper tag strip was missing.

One I have at home while still whole had carbonised and become conductive.

So, no mechanical support, no insulation: primary functions inverted!

The insulation in the set had been stabilised, it wasn't fluffy, however I had some 'Vicuclad' insulation board, that I cut sections to replace the asbestos with when I changed the dropper, It looks reasonably authentic.

Originally Posted by David G4EBT

Really two appliances in one - a radio and a room heater - buy one, get one free.

If a little circulating fan was included in the DAC90 to cool the dropper I'm sure the set would take the chill off of a small room. The DAC90A runs a lot cooler. I also have the early AC90 which is cooler running than both.

[kalee20]

Originally Posted by G.Castle

Looking carefully there is no difference in the way the sets are made, I just noted that the top of your sets dropper tag strip was missing.

Thanks for reply Greg! It is - charred, crumbled and vanished!

Originally Posted by G.Castle

If a little circulating fan was included in the DAC90 to cool the dropper I'm sure the set would take the chill off of a small room. The DAC90A runs a lot cooler. I also have the early AC90 which is cooler running than both.

Yes, the DAC90a has a 100mA heater chain not 200mA so straight away the dissipation in the dropper is halved. And it's a double whammy, because with the lower current, the valve heaters absorb more voltage to give the same heating power, so the dropper sees much less voltage to drop.

Result: a doubly-smaller resistor, and far less of a hot-spot.

The DAC90 is a bad example of design, although in hindsight it's easy to criticise. Bush did get it to market in a compact stylish cabinet in the difficult, immediate post-war months, and having done that, sat back, drew breath, went back to the drawing board and launched the '90a, getting it right with the help of Mullard's new, miniature, U-series valves!