doogie44 Posted October 21, 2019 Posted October 21, 2019 I have a box of used premium small signal NOS valves that I pulled from my components when I heard a deterioration in the sound quality of the system's presentation. Typically this involved my Leben preamplifier (although every single source electronic component has a valve somewhere). I always pulled both channel valves if I was replacing 'old' with new. Sometimes after some 5,000 hours I would do this regardless, unless I had the very long-life Telefunkens (for example). Replacement was thus for me a 'guesstimate'. Power valve replacement is not so problematic for me if there are sufficient hours elapsed as the operating life is shorter. I listen for hours every day (particularly FM radio); I rack up about 2,000 hours a year. Because of using my different sources the always-on, premium closely-matched phono valves are sometimes under-utilised. I would like to put in some 'used' ones if I am planning a marathon session without vinyl, thus extending the life of these expensive beauties. Looking at this box it's obvious that many of these premium valves may have considerable life left in them. Some are presumably ready for the bin. Is there anywhere in Sydney I could have them tested so that I end up with some backup pairs? Or visit a member with a tester for some objective results? It might be a fiddly proposition, but I am willing to compensate a fellow valve-lover with all manner of hedonistic temptations. Over to the wisdom of the Forum.
F18 Posted October 22, 2019 Posted October 22, 2019 Couple blokes up in Sydney I'm sure, if you were down in Melbourne I wouldn't mind lending a hand. Just make sure you get it tested on a proper parametric based instrument i.e. AVO VCM, Amplitrex AT-1000 or something similar and not on a basic emission tester.
aussievintage Posted October 22, 2019 Posted October 22, 2019 Just now, F18 said: Just make sure you get it tested on a proper parametric based instrument i.e. AVO VCM, Amplitrex AT-1000 or something similar and not on a basic emission tester. Just reading this I thought, maybe not necessary as they are known good valves. If he only needs to know if there's life left in them, maybe just emissions testing is all that is needed.
F18 Posted October 22, 2019 Posted October 22, 2019 (edited) 14 minutes ago, aussievintage said: Just reading this I thought, maybe not necessary as they are known good valves. If he only needs to know if there's life left in them, maybe just emissions testing is all that is needed. Emission testing is a quick way to distinguish bad tubes from good tubes, has always been that way since the 40's radio repairman days and despite common misconception that floats around online. It won't tell you how much health (transconductance, gain, gas, leakage etc) the tube exhibits or has left. A parametric tester will tell you the current draw in mA, mutural transconductance per volt mA/v and everything else above. Emission testers also don't tell the full story and test at lower than spec datasheet ideal test parameter values. Something that may show it test well on an emission tester will fail miserably on a lab/parametric tester. Of course everything calibrated and all. Edited October 22, 2019 by F18 1
aussievintage Posted October 22, 2019 Posted October 22, 2019 44 minutes ago, F18 said: Emission testing is a quick way to distinguish bad tubes from good tubes, has always been that way since the 40's radio repairman days and despite common misconception that floats around online. It won't tell you how much health (transconductance, gain, gas, leakage etc) the tube exhibits or has left. A parametric tester will tell you the current draw in mA, mutural transconductance per volt mA/v and everything else above. Emission testers also don't tell the full story and test at lower than spec datasheet ideal test parameter values. Something that may show it test well on an emission tester will fail miserably on a lab/parametric tester. Of course everything calibrated and all. I agree an emissions test does not tell you what you need to know about the health in general of any given tube. However, if a tube is purchased new, tested, and working fine, and has been used normally for a period of time - it seems that the only thing that can wear out is the emission. Anyway, that's all I meant.
F18 Posted October 22, 2019 Posted October 22, 2019 Tubes are unpredictable. Especially modern production tubes. I've had modern production tubes go bad with leakage just by having it store away on the shelf. 1
aussievintage Posted October 22, 2019 Posted October 22, 2019 17 minutes ago, F18 said: Tubes are unpredictable. Especially modern production tubes. I've had modern production tubes go bad with leakage just by having it store away on the shelf. Ah, yes. I imagine modern production is not as tightly controlled, in many cases, as was the manufacture of old tubes. Leaky and gassy tubes would be the result. Basic emissions testers often also test for leakage, and shorts, btw.
LogicprObe Posted October 22, 2019 Posted October 22, 2019 Yes, I've pulled good power tubes from my guitar amp to use a better matched pair only to have one fail on reinsertion some years later.
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