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Old 31st Dec 2002, 12:43 pm   #1
Paul Stenning
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Join Date: Dec 2002
Location: Cardiff
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Default Superglue Warning

Andy Emmerson posted the following warning on the Vintage Wireless email list:
The January 2003 issue of the excellent American magazine 'Antique Radio Classified' contains two letters warning about the dangers of using cyanoacrylate glue, with trade names such as Super Glue, for repairing valves. I think the message deserves repeating here.

Restorers often need a fast-curing glue for cementing loose glass into valve bases but danger lurks here. The problem is the difference in the coefficient of expansion of glass and of the cyanoacrylate will cause the glue to act like a hot wire glass cutter - cleanly cutting the glass off at the base when the valve heats up to full operating temperature.

The bottom line is never use this glue on any valve or tube that runs too hot (when up to full temperature) to hold your hand on the tube. This means no power output valves and no rectifiers. However, this glue is considered safe, with some reservations, for battery valves and most small signal valves, if they don't get too hot.

Cyanoacrylate glue also makes a conductive path. When applied with the tube held in a vertical position, the glue can leak down into the pin area - not a good thing. It is suggested you use the gel-type version of this glue, which does not flow as easily. Or else apply the normal fluid glue with the valve in a horizontal position. For diaply and non-functioning exhibits there's no problem at all.


Credits go to Don Harrill in the USA and Gordon Wilson in Canada for these words to the wise.
Stever Ostler posted a message confirming that he had seen this effect with a PX4 in an RGD radiogram.
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Last edited by Paul Stenning; 27th Dec 2004 at 12:10 am.
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