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> How To Tell If You Need To Have Your Tubes Replaced, Finally got an answer...
Rodnator
post Feb 20 2008, 07:10 PM
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Well, I have asked once in the past regarding new tubes in my JCM 800 50 watt amp. There were many responses but there seems to be no agreement. I was finally put in touch with a reputable Marshall certified Technician, and he told me... Obviously a degraded sound quality would be a hint but he would test if the tube had become microphonic, which means Sensitivity to vibrations causing noises and ringing. Tubes are especially prone to microphonics and will self-oscillate. He told me to turn on the amp and let it warm to operating temperature. Then, with the rear sheild removed (on my JCM Model) yours may vary, to lightly tap on the top of the warm tube, if you hear the tapping sound through the cabinet speakers, it is microphonic and are in need of change. His name is Barry and he owns a store called the Audio Clinic in Uncasville, CT. I hope this helps.
Rod


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MickeM
post Feb 20 2008, 07:35 PM
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QUOTE (Rodnator @ Feb 20 2008, 07:10 PM) *
Well, I have asked once in the past regarding new tubes in my JCM 800 50 watt amp. There were many responses but there seems to be no agreement. I was finally put in touch with a reputable Marshall certified Technician, and he told me... Obviously a degraded sound quality would be a hint but he would test if the tube had become microphonic, which means Sensitivity to vibrations causing noises and ringing. Tubes are especially prone to microphonics and will self-oscillate. He told me to turn on the amp and let it warm to operating temperature. Then, with the rear sheild removed (on my JCM Model) yours may vary, to lightly tap on the top of the warm tube, if you hear the tapping sound through the cabinet speakers, it is microphonic and are in need of change. His name is Barry and he owns a store called the Audio Clinic in Uncasville, CT. I hope this helps.
Rod

Thanks Rod, that was a good and detailed explanation. smile.gif


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KloCkWorXx
post Feb 29 2008, 03:43 PM
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also when u change power tubes wear gloves, the oil from your skin can get on them n when they get hot they can explode..


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