Another preamp tube question

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212Mavguy

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Don't throw those tubes away just yet...clean the pins first. 12ax7 pins can be cleaned with a bit of scotchbrite pot scrubber pad pinched around each pin and pulled off... or a dremel wire wheel in a dremel, holding the tool in the left hand so that the brush rotates toward the tips on the pins. If you use the dremel, wear eye protection.
 
Anomaly said:
Hey Guys! newbie here.. what are the signs to know when preamp tubes are dyin'?

I bought a nos mullard 12at7 a while back (prolly 4-5 yrs) and used it on my mic pre's for a while before shelving it..
used those same pre's yesterday on my randall rm22's blackface module on the v1, took a while to get sound out of it.. crackling
noise when I turned the gain knob. does this mean I need to dispose this tubes and buy new ones :?
If the noise occured only when you turned the pot and stopped when you stopped turning the pot, I'd say the pot might need cleaning. If the noise remained after the gain was increased, then the tube might not suitable for that position. Some noisey tubes will work in other lower gain positions in the circuit. But as 212Mav suggests, definitely try cleaning the pins first.
 

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