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    PAS3-Z noise after harm-up

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    fromans4

    Posts : 14
    Join date : 2010-04-11
    Age : 55
    Location : Petaluma, CA

    PAS3-Z noise after harm-up

    Post by fromans4 on Sun Nov 07, 2010 11:19 pm

    Hi all,

    It's been a while. After installing my PAS3-Z kit everything was good till now. After my pre-amp has been on for a few minutes (probably just long enough to warm up) static like noise starts on both channels. I think it is somehow linked to the power supply but I can't seem to pin it down. I can sometimes get it to stop temporarily by lowering the volume all the way down and tapping or wiggeling the 12X4 tube. I had a spare 12X4 tube so I tried replacing it just to see what happened, and I get the same results with the new tube.

    Any Ideas?

    Corona

    Posts : 32
    Join date : 2010-03-11

    Re: PAS3-Z noise after harm-up

    Post by Corona on Mon Nov 08, 2010 1:55 am

    Sounds like the tubes have gone microphonic maybe. Try replacing the tubes and seeing if the problem goes away. I had a similar problem.

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: PAS3-Z noise after harm-up

    Post by tubes4hifi on Tue Nov 09, 2010 11:14 pm

    could be a bad solder connection anywhere, or loose 12X4 socket pins

    fromans4

    Posts : 14
    Join date : 2010-04-11
    Age : 55
    Location : Petaluma, CA

    Re: PAS3-Z noise after harm-up

    Post by fromans4 on Tue Nov 09, 2010 11:24 pm

    Yeah, I was thinking the same thing. I will try to find the time to re-heat the solder joints on the preamp board and I am thinking about replacing the tube socket for the 12X4, it's looking pretty shabby. Thaks for your thoughts.

    fromans4

    Posts : 14
    Join date : 2010-04-11
    Age : 55
    Location : Petaluma, CA

    Re: PAS3-Z noise after harm-up

    Post by fromans4 on Sun Nov 21, 2010 10:12 pm

    OK, so to my disbelief the problem ended up being a couple of bad tubes. But after replacing the two line stage tubes and resolving my origonal problem I seemed to have picked up an increase in hiss. Is this possibly a difference in the tubes. The origonal tubes, which I had been using for a couple months, while they were working were pretty much noise free. The new tubes resolved the problem, but now I have significantly more hiss. This hiss seems to be the same at all volume levels and comes from both channels. So it is obviously more noticable at low or no volume. My origonal tubes were Electro Harmonics Gold pins and the replcement tubes are standard Electro Harmonics. I would not have thought that there would have been much difference between these tubes.

    Any ideas?

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: PAS3-Z noise after harm-up

    Post by tubes4hifi on Wed Nov 24, 2010 2:00 am

    this is just a guess but I think when they make the tubes they do a quick functional test on them and pick out the better performing ones and then gold plate the pins (at least I'd like to THINK that the gold pin tubes are actually better). I've actually got a pair of EH gold pins that are VERY noisy.
    That aside, tube noise varies greatly, although for the same manufacturer and probably same year of manufacture I'm surprise there would be that much difference. Certainly different manufacturers tubes sound slightly different. I've had good luck with both the EH and JJ tubes for budget tubes, but I do buy "tested for low noise" tubes for the phono section.
    Also in my experience almost all tubes made before around 1980 were of higher quality.
    If you have tube gear you should have a variety of spares to try, tubes are relatively low-priced.

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