CurtPalme.com Home Theater Forum

[listenlounge]

Hi everyone.
I have had my M8500 for about 7 years now - brand new rebuilds from VDC, clean as a whistle, HD145 lenses, Moome Card, the whole shebang. BUT I've NEVER used it.

Sad really, it has been in a roadcase in a shed while we built the dream house and dream theatre. The time has come.

It appears that the environment in the sealed case was less than desirable for certain metals. The damage so far is:

1. The lead X-Ray shields have corroded to the point that they needed replacement - got that covered.
2. Exposed terminals on all yokes needed a clean to remove corrosion - got that covered.
3. The adhesive metallic tape that contacts the AquaDAGS on the bell of the tubes is ruined - white powder to be precise. the grounding straps that return current to the VNB's were completely disconnected - nothing to solder on to.

Here in lies the problem. Though the metal film was disintegrated, the adhesive was not. The old adhesive, by virtue of the fact that it was interspersed the products of corrosion ( presumably lead oxide? Was the initial film lead or copper? ) It was no longer conductive. It had to be removed to make an electrical contact with the AquaDAGS.

I tried varying solvents to remove the glue, ionic, non-ionic, lipophilic, aqueous, you name it I tried it, including mechanical removal.

There was simply NO WAY to remove the adhesive without stripping the AquaDAGS. Thus the bell of the tube is now clean as a whistle.

I need a solution.

I can probably rummage up some AquaDAGS, or even create a conductive Graphite paint similar if I have too - I have a science based degree with a strong background in organic and inorganic chemistry.

BUT I wondered if I can simply use Copper Tape with conductive adhesive. I have some good quality 50mm tape here. It takes solder well.

I tested the Graphite layer before I removed it and, as expected from Carbon, the resistance of the AquaDAGS layer was significantly higher than any metal. But it obviously has great contact with the glass.

Even with the conductive adhesive, the copper tape comes in lower in resistance than the Carbon. Is the contact with (clean) glass enough to create a safe return path? Or should I repair the tube with new paint?

What does everyone think?

I do have a freshly rebuilt set of 180DVB's to use if needed. As anyone familiar with the tubes will know, the grounding solution is different between them - less paint and more foil on the DVB's. I am happy to set up the unit with the alternate set of tubes if that is the safest option.

Tim - perhaps you have thoughts on the matter?

I have promised Curt and Kal a video on the repair to add to the Advanced Procedures section, so feel free to contribute any and all thoughts to this worthy cause.

Cheers in advance

Ben

[Tim in Phoenix]

Hello

Try the copper tape, and solder the ground wires before mounting it to the glass

[gnnash]

I had a tube where the aquadag was a little short, didn't quite cover where the Barcos have grounding fingers that make contact. I sprayed on some dry graphite lube, it sticks fairly well and seemed to have a similar resistivity. Just try not to handle it in that area too much after spraying.

[cmjohnson]

My understanding is that aquadag is INSIDE the tube. The coating outside it is a carbon based conductive shielding paint.

You can get some here:

http://www.stewmac.com/Pickups_and_Electronics/Shielding/Conductive_Shielding_Paint.html

[listenlounge]

Thanks Tim.
I did indeed do a test run of tape. I cleaned the residues off the tube with 2-propanol and then applied the tape. It extends from both top corners, down the sides and across the bottom of the tube. It certainly covers more surface area than the old paint. Probably some 150 square centimetres / 25 square inches. The glue mates well with the glass. Where the tape goes around the corners of the bell it forms folded flaps/tabs. I have soldered the ground leads here. The connection is good. Given that the purpose of the setup is to form a capacitor to filter the HV and drain any excess static from the tube, do you think this is enough?
I do have some AquaDAG E in transit to use if need be, but looking at it, it is an elegant solution. If I can leave it I will. Only thing I was thinking is degradation of the glue over time.