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In the Forum: Audio Discussions
In the Thread: About the life-expectancy of the new production tubes.
Post Subject: Quality controls, and not only for the finished goodsPosted by ghpicard on: 1/7/2009
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 Romy the Cat wrote:

For instance the 2A3 has no tungsten cathodes and therefore its cathode might be “poisoned” in time if it was not properly pre-burned and some other methods were not taken care.  Those methods are expensive but they have no impact to the sound of the tube when it is new and begin to make difference only in time after the tubes worked for a while.

AFAIK, cathode poisoning only happens when a cathode is kept hot with plate voltage applied for very long periods without any current flowing through it. A classic example of this are the tubes used in the sync generators of old Tektronix oscilloscopes. Many fine oscilloscopes were gutted out to get the prized Mullard 12AU7s only to find they were totally poisoned. I can assume that they were sonically dead too.


 Romy the Cat wrote:

So, I wonder, in the today world, when people look to sell merchandizes and to move forward would it be possible that the new production of tubes juts is not doen from a perspective of longetivety? Well all know that some old tube work for many years and do fine. We do not have the stats about stable sonic performance of the new production tubes. The manufacturers it looks like say nothing about it. Furthermore, I did read a number of comments on line by the looks like experienced with DHT people who bought new production tubes and very favorable comment about them. Then they admitted that in 6 moths or a year they changed their minds and went for other tubes. I read it a few times and I wonder if there is a pattern in all of it? Is it possible that the new production of DHT tubes juts are made from “wrong” material and “wrong” techniques and the new tubes on the fields get sonically degraded much more rapidly they need to? I spoke with one audio person a year ago who suggested me a specific MC cartridge  that he traded and he said that his cartridge in contrast to any other cartridge will maintain the very same sonic signature when it was new and when I ready to be trashed. Honestly, I did not happen to try that cartridge but this comment opened for me a whole new perspective…

I do not knock in a door of any specific current tube manufacture I just would like to hear from other who has more experience with DHT then I do. I would like to know if the SONIC life-expectancy of the new production of DHT tubes might be a factor.

Rgs, Romy the caT


I think you hit the nail here. Some manufacturers say they use the same equipment and processes of old, but this is valid only (IIRC) to IDH tubes. Modern makes of older tubes are for many DHT tubes simply substitutes made by trying to reproduce the characteristic curves and tuned by ear. At least the "fancy" ones. The chinese and russians say they use the very same methods and equipment, but what we do know is that their output quality tests are dismal and we can only assume what their prime goods quality controls (and the quality of the materials themselves) might be. Even minute impurities break havoc when talking of vacuum tubes.
Nobody ever mentions aging tests of any kind. Not even simple vacuum proof and seal tests. At most what one gets is some infant mortality weeding off but that's it. Everyone assumes that glass is eternal, vacuum is too, and if measures "like" the old ones and hears (according to one person) "like" the old one, then it is *the same* as the old one.
And to me, "a 45 with more anode dissipation" is simply not a 45, and so on.

IMO, until the manufacturers get pressed to produce dependable material, something difficult to do with almost monopolic markets as we are, we are better with NOS than with reissues, unless we don't mind a 1:10 yield for new tubes.

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