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    Recent ST70 issues

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    Brap

    Posts : 91
    Join date : 2013-11-28
    Age : 62
    Location : Lisle, Illinois

    Recent ST70 issues

    Post by Brap on Wed Mar 28, 2018 11:22 am

    Bob, Just recently, the right front tube was not powering up. A slight jiggle and the rectifier flashed, fuse then blew. Replaced the rectifier and new EL34, ran fine for 2 days. Now the same right front tube is not powering up again. thoughts?
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    Bob Latino
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    Posts : 2634
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Recent ST70 issues

    Post by Bob Latino on Wed Mar 28, 2018 12:57 pm

    Brap wrote:Bob,  Just recently, the right front tube was not powering up. A slight jiggle and the rectifier flashed, fuse then blew.  Replaced the rectifier and new EL34, ran fine for 2 days. Now the same right front tube is not powering up again.  thoughts?

    The best two ideas are that the tube socket pins are dirty or you have a bad solder connection on that tube socket. Try cleaning the tube pins and the socket pins FIRST because this is the most likely problem.

    Bob
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    Brap

    Posts : 91
    Join date : 2013-11-28
    Age : 62
    Location : Lisle, Illinois

    Recent ST70 issues

    Post by Brap on Wed Mar 28, 2018 1:25 pm

    Thanks Bob -- strange it has been working just fine for over a year!. Will try that first, then go through the section on measurements wihout tubes, etc afterwards all over again.
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    Roy

    Posts : 181
    Join date : 2018-01-14
    Location : Netherlands, Europe

    Re: Recent ST70 issues

    Post by Roy on Wed Mar 28, 2018 3:19 pm

    Also perhaps check to see the tolerances of the socket hmm - failing to come up with the english word for it here - the springy metal pins/ leaves that grab the tube pins in the socket - some of the pins get hot and with age and tube rolling this may relax the female pins ( is that the word? ) to the point where they are not grabbing the pin from the tube much at all and things go amiss
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    Kentley

    Posts : 457
    Join date : 2015-03-06
    Age : 65
    Location : Worcester, MA

    Re: Recent ST70 issues

    Post by Kentley on Wed Mar 28, 2018 3:34 pm

    We like to call the process "retensioning the sockets", Roy. It is pretty easy to do with a very small jeweler's screwdriver, or, better, with a flexible surgical probe. Just take care not to bend the metal more than a tiny bit.
    Oh, and most tube sockets have tiny spaces around each pin hole for just this purpose.

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