Two blown fuses in one day

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  • #645
    chungjh
    Participant

    I sold my last amp a couple of weeks ago, so I hadn’t been playing any music for a while. Today, I hooked up a new Conrad Johnson tube amp and the left speaker from the get go was very quiet and didn’t respond to turning the bias dial (no crackle). I switched the fuse from right speaker to left and no change. I put the fuse back to the right speaker-now even the right speaker doesn’t respond to bias dial. I check the fuse and both are disconnected. Could it be that my left bias pot is some how burning any fuse that goes in there? Or am I just very unlucky?

    #650
    kingdeezie
    Participant

    I would get some new fuses to start, obviously.

    Then disconnect the amplifier and replace the fuses. Turn on each speaker and see what happens.

    If the left speaker blows again, its the plate.

    You could then switch backplates to see if the issue follows the plate amp.

    If you’ve had the amplifier hooked up during the two blown fuses, I would suspect the amplifier to be the problem.

    #651
    chungjh
    Participant

    I have ordered new fuses. But, Dr. West thinks there is a possibility that the bias supply may be defective. These bias supplies have been in use for the past several years but non have failed yet.

    #652
    John V
    Participant

    Was the response to you from Dr. West within the past few days?

    Thx,
    John

    #653
    chungjh
    Participant

    Yesterday. So, these regulated bias supply must not have been used in the old SL speakers.

    #654
    kingdeezie
    Participant

    Seems odd the bias supply would just go bad to that extent where it’s blowing fuses.

    Is the Conrad amp brand new? I would have it checked out.

    #655
    chungjh
    Participant

    I think the fuse blew before I hooked it up to CJ amp, which was playing fine in a friend’s house. This speaker had lower bias for a long time compared to the other one. When I exchanged the fuse with the other speaker, this bias supply must have burned the fuse from the working speaker. I don’t think it is the amp, because the speaker sounded very weak from the get go. Everyone on the SLOG should look out for this possibility if it happens.

    #656
    kingdeezie
    Participant

    Did Dr. West just recommend you send it in for repair?

    #657
    chungjh
    Participant

    I am going to have the bias supply shipped to me. I don’t think it is difficult to replace.

    #658
    grg3939
    Participant

    Hi. Very easy to change it out, assuming you have decent soldering skills. Some years ago I had a bias supply fail and Roger told me that the replacement supply was of reversed polarity vs my original. Since they were a from a new supplier, I decided to order two so both speakers would have the exact same parts. (Audio Nervosa?) Besides, they are not expensive. Since the new ones had reversed the polarity, in order to maintain proper absolute phase, one simply needs to reverse the amp to speaker cable connections. If SL does not mention this, be sure to ask them if the new supply maintains the same polarity as your failed one, or if it is reversed. Depending how old your speakers are, you may already have the newer supplies anyway, which, in that case you do not need to worry about this.

    #659
    lotus123
    Participant

    @grg3939, what vintage was your SL that had a bia supply failure?
    What model?

    #660
    chungjh
    Participant

    2016 M545

    #661
    grg3939
    Participant

    Model U3 (the only pair ever made) over 20 yrs old. But I updated the toroids and PX panels and the bias supplies (2011).

    #662
    chungjh
    Participant

    How long after manufacture was the bias supply replaced on your U3?

    #664
    kingdeezie
    Participant

    Any updates? Did the new fuses blow as well?

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