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Old 12th March 2012, 02:19 PM   #1
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Default symptom of a dying (gain) tube

what are the symptoms of an overaged tube in a preamp circuit? is it diminished bass/mid? i think i have some tubes that need changing.
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Old 12th March 2012, 02:51 PM   #2
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It sounds more like a capacitor that is changing value.
As a tube ages, the emission will decrease. The effect will be lower gain and/or the early onset of clipping at high levels.
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Old 12th March 2012, 03:12 PM   #3
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i should mention that the gain is also lower. it takes about 3 times the turn of the volume that is usually required to reach the desired listening level.

the whole component is fairly new and the caps should be well within their lifespan.

Last edited by PreSapian; 12th March 2012 at 03:17 PM.
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Old 12th March 2012, 03:33 PM   #4
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May be that the +B is too low because of a bad cap or a false contact in the heaters rail so the tubes take more time to get normal cathode temperature.
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Old 12th March 2012, 05:14 PM   #5
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You might get more distortion at levels below clipping. It is conceivable that your ears may perceive this as a frequency response problem, but it isn't.
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