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    crackling in left channel

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    MartinD18GE

    Posts : 1
    Join date : 2011-04-15

    crackling in left channel

    Post by MartinD18GE on Sun Apr 17, 2011 4:07 pm

    I am a long time ST-70 user. It has been awhile since I have done any work on my unit other than changing tubes. Last week the left channel started making a crackling noise. Changing preamps didn't remove the noise. The 7199 on that side has always been sensitive. I pulled it and replaced it with a spare. The noise got worse. I removed the original PC-3 and replaced it with a 6GH8A board that I have had since the 90's. The unit was quiet for ten minutes, so I turned on the preamp. The crackling noise came back and stayed even after I shut off the preamp. I switched the tubes left to right and the noise stayed in the left channel.

    Does anyone have any thoughts? Am I looking at a quad filter cap, power supply or what?

    Thanks,

    Sean

    Bob Latino
    Admin

    Posts : 2413
    Join date : 2008-11-26
    Location : Massachusetts

    Re: crackling in left channel

    Post by Bob Latino on Sun Apr 17, 2011 5:05 pm

    Try cleaning that 7199 tube socket. The best stuff to use is Caig Pro-Gold. I think Radio Shack still sells it.

    After many years dust collects down in those tube sockets and sometimes you run into a partial contact issue with one or more socket pins. This is more common on 9 pin and 7 pin small sockets than the larger octal tube sockets found on the ST-70 output tubes. The reason being those little pins on the socket don't have much contact surface area and as such, they are more likely to give a partial contact problem.

    Years ago, when there was no Caig Pro Gold cleaner, what we did was to spray the PINS ON THE TUBE with WD-40 and wipe off the excess WD-40 so it's not drippy. Then insert the tube in and out of the socket a few times and then wipe off the pins until they are dry. Many times this will correct a contact issue between tube and socket. Sometimes you need two or 3 cycles of this procedure before the socket is completely clean.

    Bob

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