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    Building, troubleshooting and testing of these amplifiers should only be
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6sn7gtb problem

nkg

Member
2004-07-20 3:22 pm
perth
My 2a3 amp has been working well untill the last couple of days I turn it on and after about 10 seconds it makes this noise like a needle has been draged across a record it doesn't last very long less than a second then everything is fine . I changed 6sn7gtb which is the driver for the 2a3 for another one and the noise is gone . It only happened one one channel and was curious if anybody could tell what causes this .
Thanks
nigel
 
nkg said:
My 2a3 amp has been working well untill the last couple of days I turn it on and after about 10 seconds it makes this noise like a needle has been draged across a record it doesn't last very long less than a second then everything is fine . I changed 6sn7gtb which is the driver for the 2a3 for another one and the noise is gone . It only happened one one channel and was curious if anybody could tell what causes this .
Thanks
nigel

Tube gremlins.;)
 

gain wire

Member
2004-11-27 4:04 am
NCR
I am by no means a tube expert, but I think that there are two possible causes. First, your 6sn7gtb has a loose/misaligned heater/filament inside the cathode, and until it reaches its stable temperature (approximately 11 seconds) it is actually contacting the cathode. When it(the filament) reaches its temperature and is all lit up, it straightens out and no longer contacts the inner walls of the cathode.
Second: The tube has a loose wire bond inside, which might be affected by warm-up temperature also. May I ask what manufacturer made these 6sn7gtb?
I hope my 2 cents worth was worth something. Also, if anything in my hypothesis is wrong or inaccurate, someone let me know.

Thanks