Cataracts on Camera viewfinder CRT tubes
 

Hello,

On all my marconi MKVIII color cameras and the rca tk45's, (1970's) the viewfinder tubes have a yucky bubbling under the surface right the way across, what i beleive is called CRT cataracts.

I wondered what is the best way to fix this and what are the dangers of doing so?

The marconi tubes seem to have a front glass plate which is attached around the edges by what looks like thick yellow gap filler type foamy stuff, whilst the rca tk45's i havent actually tried to open and look yet.

Someone mentioned acetone, but how do you apply it and get it inside? ...just dip the CRT face down into some until it dissolves it?

apart from which method works best, i would also like to know how things are from a safety perspective, are these relatively small tubes from the 70's a huge risk for implosion still? - if you remove the glass faceplate...are these there for safety and must be placed back? or by the 70's were these purely decorative and not so much for safety as the older crt's were?

any advice is appreciated


James in australia
www.oldtvgear.com

Any way to get the tube type number? Then maybe you could find a spec and determine if the faceplate was an add-on, perhaps to reduce glare and/or for safety.

crt spots
 

Hi James

The spots you see are a defect in the manufacture/design. Some of the early CRTs have a defect with the tube faceplate bonding. This leads to spots on between the tube and the front glass. I have a number of cameras and spare tubes in the collection that are affected, some of them very badly. Very early tubes used in the MkV cameras seem less affected and very late tubes are unaffected (yet). The Marconi MkIX is affected as well and cameras from other manufactures too. It is a real problem.

The worst case I have seen http://www.tvcameramuseum.org/link/1...k103large2.htm

7" viewfinders without the bonded on face plate had a glass or perspex window in front of the tube with a clamp band around the tube for fixing. In the bonded tube the mounting flange is part of the fixing.

I have sometimes thought of picking open the seals at the edge and cleaning it all out, but I can't recommend this as the tube might go bang! which is to be avoided.

The Marconi MkVIII tube number is PMT69 I am sure there is a standard equiv number in the MW xxx range.

I would be interested to know how you get on.

Brian S

Eeeuww, gross ! (grin)

Somebody I know (name witheld to protect the guilty) removed a bonded faceplate by force and survived to tell the tale.

here is a photo of one of the viewfinders on the Mark 8 cameras :(

The cameramen must have got generous doses of X-Rays staring close up into those things !

actually, no...(correct me if i am wrong) but from what i understand the little xrays a CRT creates is strongest near the neck of the tube and very little if any gets through the thick glass at the front.

Either way...still dont know how to get rid of these bubbles, on the mark 8 camera above it seems to have a flat plate of glass over the tube which is glued in place around the edges by a yellowish gap filler foam type substance

Even as icky & gross as it is, you may just have to live w/it, the risk of breaking the prolly Unobtanium camera viewfinder CRT is pretty great, I would think.