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    VTA 70 repaired! Good news!

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    j4570

    Posts : 141
    Join date : 2010-08-30

    VTA 70 repaired! Good news!

    Post by j4570 on Mon Jun 06, 2016 1:54 pm

    Everyone,

    I just wanted to make this post to remind everyone of checking out your amp periodically.  My amp sits up high in the bedroom and never gets checked really.  I think once in 5 years I have checked the bias.  Well, about 2 months ago it started blowing fuses, like 5-10 seconds after startup.  I only had a few spare fuses, so after blowing a couple, I couldn't figure it out and decided to wait until I had time to pull it to the garage and put it on the bench.  Finally, I pulled it this weekend and discovered a few things:

    1)  There was a metal light hoop that fell behind the amp (shorting the outputs????).  Don't ask me how it got there, but when I changed the fuse I don't think it was there so I'm pretty sure that wasn't it.  However, I'm not sure I really pulled the amp out to change the fuse.  I might have just done the old reach around.

    2)   The rectifier seemed really loose.  I tested it and it was ok on my emission tester. I went ahead and installed the diode modification while I had the amp on the bench and opened up.   I retensioned the pins on the rectifier socket, replaced the fuse, and when through the startup procedure.  Amazingly, the amp worked fine!  The bias was a little off on the left channel but that was it.  

    3)  Installed Genalex U77 to replace the Ruby 5AR4 (Shugang?) rectifier.  The Ruby was fine, but I had gotten the Genalex to install.  Warmed up amp and rebiased.  Didn't notice any sound change.  

    4)  The amp was really dusty, even using a handtowel as a cover (I always unplug it, don't worry).  I need to make a cover for it (I know there is a place that makes them, but I just like using vinyl).

    So there it goes, it pays to clean your amp once in while and perform a check up.  I'm glad it's working again.  

    Have slow blow fuses on hand.  They are not that easy to find now that Radio Shack isn't around.  I have plenty now.......
    Have a spare rectifier for testing.  Mine turned out ok, but I was a little nervous and putting the U77 in there for testing purposes if it had turned out bad.

    So my best guess is the loose pins on the rectifier, or that metal thing behind the amp.  

    Have a good day!

    Jason

      Current date/time is Sat Dec 10, 2016 12:33 pm