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Old 11th April 2009, 04:46 PM   #1
tomat is offline tomat  Indonesia
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Default need help with tubes problem

i was install an nos tubes on my preamp ,a few minutes after i'm powering up the preamp ,i hear loud cracking sound on one of my speaker and the woofer move like pumping,what causing that?
anybody can help?

thanks a lot
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Old 12th April 2009, 01:07 AM   #2
tomat is offline tomat  Indonesia
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anybody?,and can we detect damage tube without tube tester?

thanks
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Old 12th April 2009, 02:11 AM   #3
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You need to give much more detail. This was a working preamp, and then what you did was replace one existing tube with an NOS tube of the same type and it began to act as you described? What preamp model and tube are we discussing?
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Old 12th April 2009, 09:17 AM   #4
tomat is offline tomat  Indonesia
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Quote:
Originally posted by leadbelly
You need to give much more detail. This was a working preamp, and then what you did was replace one existing tube with an NOS tube of the same type and it began to act as you described? What preamp model and tube are we discussing?


yes,that is working preamp,i was using electro harmonix 6sn7 previously,and then i change to rca grey glass 6sn7,the problem begin after that.
i was check the voltage on my preamp ,120v from plate to cathode ,the current is 3ma,filament voltage is 6volt.
i have at least 4 pairs nos rca 6sn7 tubes and they are all have same problem,cracking sound and then make the woofer move like pumping.
i was buying that tubes from trusted vendor in canada,and they said that they was test the all tubes before they ship

thanks
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Old 12th April 2009, 01:06 PM   #5
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And without preamp, is there the same problem?
Put left out preamp to right in of power amp, and
right out to left in of pow. amp. Is there the same?
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Old 15th April 2009, 11:12 AM   #6
tomat is offline tomat  Indonesia
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Quote:
Originally posted by azazello
And without preamp, is there the same problem?
Put left out preamp to right in of power amp, and
right out to left in of pow. amp. Is there the same?

i have change to other tubes,the problem is disappear,so i guess the problems came from the tubes.
my question,can we know if the tubes had a problem without using a tube tester?.cause the tester is expensive
sorry for my poor english

thanks a lot
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Old 15th April 2009, 12:00 PM   #7
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The woofer pumping in and out is caused by a term called motorboating, low frequency oscillation. Have a search for possible causes related to that.
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