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    Please help with my st 70



    Posts : 4
    Join date : 2015-03-05

    Please help with my st 70

    Post by cheehpogi on Fri Jul 10, 2015 7:21 pm

    Posted this in another forum.
    First thing that happened was I mistakenly put a different rectifier tube in it, the PT started to rattle and I immediately turned the unit off ( less than sec.) Then I put in the right tube this time and it played with no problem, after a few minutes the fused blew up. I replaced the fuse and turn it on, I can hear tapping sound on my left speaker and the fuse blew up. I tested all my tubes and all are within normal limits on my heathkit tube tester. Did some testing, just with the rectifier tube and it stayed on with no problem. With all the tubes in the amp the left tubes both the front and rear started red plating. I remove both tubes on the right and power it on again, still red plating. Did the same test on the right and both right tubes are not red plating ( doing the test with no load). What could be the problem? Could it be my driver board because all main caps are not giving me any reading on the tester. Need advise. Thanks in advance.


    Posts : 1466
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Please help with my st 70

    Post by sKiZo on Fri Jul 10, 2015 9:51 pm

    What rectifier did you plug in that you think started all this?

    First thing I'd check is the bias resistors connected to pin #8 on each power socket. Those are meant to be sacrificial to protect the amp.

      Current date/time is Mon Jun 18, 2018 4:46 pm