6sn7gtb problem

[nkg]

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

[G]

Originally posted by nkg
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]

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

[nkg]

Hi gain-wire
Thanks for your reply it was a Phillips .
nigel

[nkg]

And there I thought G stands for Genius what a let down its only Gavin.
nkg

[Cycline3]

Sometimes it is as simple as a dirty tube socket connection - that moving the tube or removing and replacing it - cures right up.