Flethc - Interesting post and pretty relelvant to a nagging question on my mind. One of my CJ amps appeared to have blown several EL34's due to a volatage surge last month. The bias lights turned red on 5 out of the 8 tubes, and the amp shut down. I replaced the tubes but kept the old ones to test when my newly purchased B&K 747 testes arrived. Well, the tester sez they are fine! There are no shorts, no gas leaks and the Gm and Tube Life tests are fine. The tester is a fully refubished, like new unit bought form B&K Test Equipment. I double checked the calibration and it is indeed pristine. Sooo..why did the amp declare the tubes "bad"?
Tube Myths- Tested Tubes
By the many emails, thanking me for the info, I have decided, to not let criticism, of my supposed intentions, stop me from posting, information.
Almost all customers, of mine, asked if a tube, has been tested. Most ask for the best testing tube, thinking, that it would mean, that it is , the best tube, as far as longevity, sonics, noise, etc. Testing tubes, will tell you, whether a tube, is within specs. It will give you a reading, that you can correllate, with the manufacturers specs, to determine if a tube, is good, and useable, or defective. It will not tell you, how good a tube, will sound. It will not tell you, how long a tube, will last. Noise testing, will not guarentee, that a tube, will not be noisy, as some circuits, place demands, on tubes, that no amount of testing, can predict, how they will act. Don't get me wrong, testing is invalueable, because it narrows the field, and gives the user, a much better chance, of a tube, that will meet their needs. It just not a carte blanche guarentee, that a better testing tube,ie; balanced sections,emissions, will be a better tube. Because a tube, tests higher, will not mean, that it will have a longer service life, than one that tests lower.
There are many tests, that a tube can be subjected to. The more testing, that is done, the better chance, of predicting, how the tube, will act. But none can tell you, how it will sound. That can only be determined, by the tube, being placed in the intended circuit, allowed to breakin, and listened to. And because circuits, run tubes differently, it's difficult to determine, that operation, in one circuit, verifies the same operation, in another. For instance, a tube operated at 240v, might be just fine, but at 310v, it shows some problems. Or a tube at 290v, is perfect, but at 210v, it exhibits problems. In a perfect world, it would be just fine, throughout it's entire operating range, but this is the tube world, we live in. Enjoy.
Almost all customers, of mine, asked if a tube, has been tested. Most ask for the best testing tube, thinking, that it would mean, that it is , the best tube, as far as longevity, sonics, noise, etc. Testing tubes, will tell you, whether a tube, is within specs. It will give you a reading, that you can correllate, with the manufacturers specs, to determine if a tube, is good, and useable, or defective. It will not tell you, how good a tube, will sound. It will not tell you, how long a tube, will last. Noise testing, will not guarentee, that a tube, will not be noisy, as some circuits, place demands, on tubes, that no amount of testing, can predict, how they will act. Don't get me wrong, testing is invalueable, because it narrows the field, and gives the user, a much better chance, of a tube, that will meet their needs. It just not a carte blanche guarentee, that a better testing tube,ie; balanced sections,emissions, will be a better tube. Because a tube, tests higher, will not mean, that it will have a longer service life, than one that tests lower.
There are many tests, that a tube can be subjected to. The more testing, that is done, the better chance, of predicting, how the tube, will act. But none can tell you, how it will sound. That can only be determined, by the tube, being placed in the intended circuit, allowed to breakin, and listened to. And because circuits, run tubes differently, it's difficult to determine, that operation, in one circuit, verifies the same operation, in another. For instance, a tube operated at 240v, might be just fine, but at 310v, it shows some problems. Or a tube at 290v, is perfect, but at 210v, it exhibits problems. In a perfect world, it would be just fine, throughout it's entire operating range, but this is the tube world, we live in. Enjoy.
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