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    Rectifier and blown fuse

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    jimmeq

    Posts : 46
    Join date : 2017-02-24

    Rectifier and blown fuse Empty Rectifier and blown fuse

    Post by jimmeq on Sat Mar 14, 2020 7:45 am

    When a rectifier goes south, does the fuse usually blow too?


    Here's why I ask:

    Upon powering on my ST-120, I heard a slight crackle and the rectifier arced. The fuse was blown as well. I replaced the tube and fuse and again saw the rectifier arcing then the fuse blew. (It was not a known good rectifier used to replace the first one.)

    I re-flowed the solder on the cap*, replaced the fuse and inserted a new Sino 5AR4. The amp works fine now. Typical voltage at my house is 117 - 120V.


    * I had replaced this several months ago and it being the most recent change, thought it might be the problem.
    peterh
    peterh

    Posts : 1280
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Rectifier and blown fuse Empty Re: Rectifier and blown fuse

    Post by peterh on Sat Mar 14, 2020 8:05 am

    jimmeq wrote:When a rectifier goes south, does the fuse usually blow too?


    Here's why I ask:

    Upon powering on my ST-120, I heard a slight crackle and the rectifier arced. The fuse was blown as well. I replaced the tube and fuse and again saw the rectifier arcing then the fuse blew. (It was not a known good rectifier used to replace the first one.)

    I re-flowed the solder on the cap*, replaced the fuse and inserted a new Sino 5AR4. The amp works fine now. Typical voltage at my house is 117 - 120V.


    * I had replaced this several months ago and it being the most recent change, thought it might be the problem.
    The 5AR4 in VTA-120 and to a less extent VTA-70 is working hard.

    A rectifier that has arched is consumed and should be junked.

    The yellow sheet mod seems to make rectifiers last longer as flash-over will not
    lead to destruction. Recommended !
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    jimmeq

    Posts : 46
    Join date : 2017-02-24

    Rectifier and blown fuse Empty Re: Rectifier and blown fuse

    Post by jimmeq on Tue Mar 17, 2020 7:04 am

    Thanks Peterh. I guess it's somewhat of a rhetorical question because it happened twice but I'm a tube amp beginner. I'm just curious about the fuse blowing when a rectifier goes south. I'll increase my fuse stock. I plan to upgrade to a Tung-Sol  5AR4 and keep the Sino as a spare.

    I do have a SS but just love the look of a tube rectifier. (I did do a search in the Basket but did not find any info on fuses blowing when a rectifier arc's.)


    *I'd have responded sooner but I had to get skiing before all the ski areas shut down because of covid-19.
    peterh
    peterh

    Posts : 1280
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Rectifier and blown fuse Empty Re: Rectifier and blown fuse

    Post by peterh on Tue Mar 17, 2020 9:33 am

    jimmeq wrote:Thanks Peterh. I guess it's somewhat of a rhetorical question because it happened twice but I'm a tube amp beginner. I'm just curious about the fuse blowing when a rectifier goes south. I'll increase my fuse stock. I plan to upgrade to a Tung-Sol  5AR4 and keep the Sino as a spare.

    I do have a SS but just love the look of a tube rectifier. (I did do a search in the Basket but did not find any info on fuses blowing when a rectifier arc's.)


    *I'd have responded sooner but I had to get skiing before all the ski areas shut down because of covid-19.

    Do install the "yellow sheet mod" where a pair of 1n4007 or un4007 is connected in series
    with the 5ar4 anodes. This prevents huge currents if the tube flashes thereby saving
    fuse and tube.

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    Mangaman80

    Posts : 2
    Join date : 2017-03-01

    Rectifier and blown fuse Empty Re: Rectifier and blown fuse

    Post by Mangaman80 on Tue Mar 17, 2020 11:09 am

    What’s the yellow sheet mod? I have the 120 and haven’t been on the forum in a while? I had rectifier issues early on but that has since slowed and I haven’t changed my rectifier out in a long time.

    Thanks!
    Mark
    Bob Latino
    Bob Latino
    Admin

    Posts : 2890
    Join date : 2008-11-26
    Location : Massachusetts

    Rectifier and blown fuse Empty Re: Rectifier and blown fuse

    Post by Bob Latino on Tue Mar 17, 2020 11:27 am

    Mangaman80 wrote:What’s the yellow sheet mod? I have the 120 and haven’t been on the forum in a while? I had rectifier issues early on but that has since slowed and I haven’t changed my rectifier out in a long time.

    Thanks!
    Mark

    Check the link below ..

    Tube rectifier yellow sheet diode mod

    Bob

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