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I still would hesitant to short the scene and anode and it would require a very sever control of the tubes. The problem is that it would be necessary to do not only then they new (it not too difficult to put then before a fast scope and to see if they are quiet) but also to check them periodically while they are in use.

Burning the 10 channels of Melquiades for 2 years I do detect that a dying 6E5P/6E6P gains some intermediate noise when it goes south. What is interesting is that 6E5P do it different then other UFH tubes that I used.

For instance the 7788 ultra-high transconductance pentodes (E810F) what they go microphonics did in a gentle way, reacting initially juts to disturbance and then get worse and worse. The WE417 behaved differently: it begin to produce the UHF pings – very unpleasant for tweeters effect…. The 6E5P what got old begin to “boil MF”. I mean from time to time the MF channel begins to pick some “bubbling MF noise” for a few seconds and it is a good indicator that the tube is beginning to go down. Uselessly in my Milqs the 6E5P lives for a little bit less then a year. Ironically but the 6E6P-DR does sooner then the 6E5P….

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