[ohohyodafarted]

I have the only 21AX that has had a leak repaired. The leak was on the weld where the funnel is joined to the front section. John Yurkon did the repair to the leak and did a standard rebuild procedure with a new gun assembly. That tube is now in my recently restored CTC4 Cheltenham and it is producing a very strong, bright picture. It is our conjecture that it would be a rare occurrence for a 21AX to have a glass to metal interface leak. Most all of the leak failures are occurring in the weld between the funnel and the front section of the tube. If a 21AX has not leaked thus far, it is unlikely that it will leak in the future, barring careless handling causing physical damage to the weld.

As for the 15G; two types of leaks can occur. The first type is a failure of the weld or a failure of the fusion weld of the reinforcement ring in the ultor ring assembly. The second common 15G leak is a failure of the glass to metal bond. I have seen a number of 15G tubes that have small fissures in the glass to metal bond. These can propagate due to large temperature swings or from physical stress. If the glass to metal bonds are free of small fissures in the glass I would say there is a high probability that the tube will stay leak free provided it is not subjected to large temperature swings or any physical stress. One other issue is moisture. About half the leaker 15G's I have examined, have been subjected to moisture which has caused rust to form on the ultor ring to varying degrees. The rust between the laminations of the ultor ring expands between the laminations and causes physical stress. The stress results in micro cracks in the glass where the glass is bonded to the metal ultor ring, thus causing a leak. So if you have a good 15G, keep it in a temperature controlled dry environment and do not subject it to any undue physical stress.