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    Glass piece inside output tube and tube placement

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    James_Weir

    Posts : 8
    Join date : 2016-07-01

    Glass piece inside output tube and tube placement

    Post by James_Weir on Mon Jul 18, 2016 2:19 pm

    For 6 months I've been using a friend's stock st70 while I get everything together for one of my own. He needed it back so I removed my tubes very gently, but noticed a small piece of glass rattling around in one. It looks round on one side and flat on the other like it ended up in there as a flaw during manufacture. 4 questions:

    1. Is there any chance this tube is fine?

    2. Without special testing equipment, will I be able to tell if it's bad immediately (visually, audibly) and is there any danger to my unit if it is?

    3. If I replace it do I need to buy a new matched pair? Not sure if the individual biasing of the VTA pcb minimizes the need for matched pairs or if that has nothing to do with it.

    4. If I need to replace them in pairs, does the matched pair go on the same side or the same position on each side? It makes most sense that two matched pairs with one pair in the rear position for each side and one pair in the front position for each side would yield identical results on the left and right, but somehow I feel like I might be wrong.

    I'm just getting my feet wet here, so thanks for the help with this and previous posts.

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Glass piece inside output tube and tube placement

    Post by peterh on Mon Jul 18, 2016 3:24 pm

    James_Weir wrote:For 6 months I've been using a friend's stock st70 while I get everything together for one of my own. He needed it back so I removed my tubes very gently, but noticed a small piece of glass rattling around in one. It looks round on one side and flat on the other like it ended up in there as a flaw during manufacture. 4 questions:

    1. Is there any chance this tube is fine?

    2. Without special testing equipment, will I be able to tell if it's bad immediately (visually, audibly) and is there any danger to my unit if it is?

    3. If I replace it do I need to buy a new matched pair? Not sure if the individual biasing of the VTA pcb minimizes the need for matched pairs or if that has nothing to do with it.

    4. If I need to replace them in pairs, does the matched pair go on the same side or the same position on each side? It makes most sense that two matched pairs with one pair in the rear position for each side and one pair in the front position for each side would yield identical results on the left and right, but somehow I feel like I might be wrong.

    I'm just getting my feet wet here, so thanks for the help with this and previous posts.

    1/ yes. The loose piece may settle at the bottom. Transport may however relocate the item to a place where it will distrurb.
    2/ no, no danger
    3/ yes, matched pair, and 4/ on each side

    James_Weir

    Posts : 8
    Join date : 2016-07-01

    Re: Glass piece inside output tube and tube placement

    Post by James_Weir on Mon Jul 18, 2016 3:52 pm

    Few things are as satisfying as getting an efficient answer to a question. Thanks for the help.

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