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Old 6th Feb 2020, 11:55 am   #1
Helder Crespo
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Default Cleaning aquadag coating on Bush TV22 tube

Hi
I would like to have your advice on cleaning the aquadag coating on my Bush TV22 tube (MW-12-16). The bottom of the tube is spotless, but the top is invariably dirty and dusty. From a small test, I noticed that solvents such as meths or isopropyl alcohol appear to dissolve the coating, so this looks like a clear no no.
What are your suggestions? Dry brushing alone, for instance? Or is there something else that can safely be used?
Thanks!
Helder
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Old 6th Feb 2020, 2:38 pm   #2
Heatercathodeshort
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Default Re: Cleaning aquadag coating on Bush TV22 tube

Just dust it off. Any attempt to clean it will result in it disintegrating completely. Keep it DRY! It is after all a dirty gray looking material even when new.
'DAG' may be available in small quantities from it's makers. Google ELECTRODAG for some useful information. John.
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Old 6th Feb 2020, 2:57 pm   #3
Helder Crespo
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Default Re: Cleaning aquadag coating on Bush TV22 tube

Thanks John!
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Old 10th Feb 2020, 2:47 pm   #4
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Default Re: Cleaning aquadag coating on Bush TV22 tube

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Originally Posted by Heatercathodeshort View Post
Just dust it off. Any attempt to clean it will result in it disintegrating completely. Keep it DRY! It is after all a dirty gray looking material even when new.
'DAG' may be available in small quantities from it's makers. Google ELECTRODAG for some useful information. John.
How about this? It appears to have similar electrical characteristics to Electrodag. Would it be adequate for repairing a couple of small holes on the external coating of my tube?
https://www.ebay.co.uk/itm/AQUADAG-C...H/261808496366
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Old 10th Feb 2020, 5:32 pm   #5
dazzlevision
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Default Re: Cleaning aquadag coating on Bush TV22 tube

Or this: https://www.rapidonline.com/Kontakt-...SABEgIpkvD_BwE
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Old 10th Feb 2020, 6:17 pm   #6
Helder Crespo
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Default Re: Cleaning aquadag coating on Bush TV22 tube

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Thanks! It's also cheaper, but aerosol, so great for large areas but maybe not the best for repairing small holes.
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Old 11th Feb 2020, 11:27 am   #7
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Default Re: Cleaning aquadag coating on Bush TV22 tube

It may not stick to glass. RS RF shielding is brilliant but it just falls off glass when dry. Maybe a primer coat will help but I'm wondering if it might have an odd effect due to the paint forming a second capacitor.
Why worry about a couple of small holes? They will have absolutely no effect on the performance. If it works, leave it alone. John.
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Old 11th Feb 2020, 4:00 pm   #8
Helder Crespo
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Default Re: Cleaning aquadag coating on Bush TV22 tube

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Originally Posted by Heatercathodeshort View Post
It may not stick to glass. RS RF shielding is brilliant but it just falls off glass when dry. Maybe a primer coat will help but I'm wondering if it might have an odd effect due to the paint forming a second capacitor.
Why worry about a couple of small holes? They will have absolutely no effect on the performance. If it works, leave it alone. John.
Thanks John. My set definitely works. My main concern was potential field enhancement effects at the hole edges and related corona discharges. I prefer to leave it alone, of course, if this does not comprise performance nor safety. Due to my lack of experience, I prefer to be on the safe side.
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Old 11th Feb 2020, 5:18 pm   #9
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Default Re: Cleaning aquadag coating on Bush TV22 tube

Helder,

There will be no corona effects, because the aquadag layer does not carry high voltage.
I fully agree with John: a few holes in the layer or small parts of the conductive layer surface missing will not make a difference.
Basically it is just the EHT smoothing capacitor (capacitor between graphite layer on the inside of the CRT and ditto on the outside).
Just make sure that the layer makes good contact with ground potential (chassis).
Not all CRTs have the outer conductive layer, and thus require a separate smoothing capacitor (suitable for the EHT voltage). The Ekco TMB272 is an example.

Graphit 33 will adhere to the glass and works excellently.
Most DAGs are waterborne products, and do adhere to the glass, but are not really "glued". It is just colloidal graphite in water.

Jac
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Old 11th Feb 2020, 8:32 pm   #10
Helder Crespo
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Default Re: Cleaning aquadag coating on Bush TV22 tube

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Originally Posted by Jac View Post
Helder,

There will be no corona effects, because the aquadag layer does not carry high voltage.
I fully agree with John: a few holes in the layer or small parts of the conductive layer surface missing will not make a difference.
Basically it is just the EHT smoothing capacitor (capacitor between graphite layer on the inside of the CRT and ditto on the outside).
Just make sure that the layer makes good contact with ground potential (chassis).
Not all CRTs have the outer conductive layer, and thus require a separate smoothing capacitor (suitable for the EHT voltage). The Ekco TMB272 is an example.

Graphit 33 will adhere to the glass and works excellently.
Most DAGs are waterborne products, and do adhere to the glass, but are not really "glued". It is just colloidal graphite in water.

Jac
Hi Jac
Thanks for your detailed reply! I understand that the only way for the top "plate" of the smoothing capacitor to be at a high potential is in case of a bad connection to the "ground" (chassis), which is of course a bad thing to have regardless of any holes. I will check this on my set (already on my to-do list for the weekend).
As for the holes, they are a bit unsightly, but that's all, as the resulting change in capacity is minimal (area of the holes / total area of the rest of the coating). Thanks for the tip on the Graphit 33 spray.
Helder
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