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    finally happened-up in flames!

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    kevinmi

    Posts : 78
    Join date : 2009-11-17

    finally happened-up in flames!

    Post by kevinmi on Sun Oct 07, 2018 10:56 am

    Well not actually flames, but I lost a vintage Tung-Sol 6550 tube in my ST-120. Red hot and a terrible noise that sent my dog running for cover! It blew the fuse, but not sure if it took out the rectifier tube or resistor.
     I ordered the auto bias board today (hindsight is 20/20), so hopefully I won't have to go through this again!
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    CletusB

    Posts : 191
    Join date : 2018-02-11
    Age : 63
    Location : Trinidad & Tobago

    Re: finally happened-up in flames!

    Post by CletusB on Sun Oct 07, 2018 11:36 am

    kevinmi wrote:Well not actually flames, but I lost a vintage Tung-Sol 6550 tube in my ST-120. Red hot and a terrible noise that sent my dog running for cover! It blew the fuse, but not sure if it took out the rectifier tube or resistor.
     I ordered the auto bias board today (hindsight is 20/20), so hopefully I won't have to go through this again!
    Sorry to hear that,  let us know what you find out was the cause please. scratch
    If it was a defect in the tube, I can't see how the auto bias would mitigate that.  Good old Dynacos and McIntoshs are still out there running on simple rectification/filtration systems with no unusual tube issues.
    I wipe down my ST-120 every Saturday morning (there's not a fingerprint on it) and check/adjust the bias as part of my breakfast ritual Laughing

    Love the turntable in you avatar!   ...I really miss my Delphi! Crying or Very sad
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    ArlanB

    Posts : 67
    Join date : 2011-01-23
    Age : 71
    Location : Santa Cruz, California

    Re: finally happened-up in flames!

    Post by ArlanB on Sun Oct 07, 2018 8:42 pm

    Over the years I have had 5 power tube failures 4 of which were internal failures with bright flashes taking out both the power tube and the 5AR4 and only one episode of red plating involving only the offending tube.  The flash failures usually occurred within 2 weeks to 7 months of installation, the red plate episode was with a 4&1/2 year old tube, probably close to end of life. All of the episodes have ended positively with no involvement of internal circuits after full check of all associated components.  Can attest to well designed circuits with tough components able to withstand todays modern power tubes with less than ideal construction standards.
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    Peter W.

    Posts : 933
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: finally happened-up in flames!

    Post by Peter W. on Mon Oct 08, 2018 10:33 am

    ArlanB wrote:Over the years I have had 5 power tube failures 4 of which were internal failures with bright flashes taking out both the power tube and the 5AR4 and only one episode of red plating involving only the offending tube.  The flash failures usually occurred within 2 weeks to 7 months of installation  (??!!), the red plate episode was with a 4&1/2 year old tube, probably close to end of life. All of the episodes have ended positively with no involvement of internal circuits after full check of all associated components.  Can attest to well designed circuits with tough components able to withstand todays modern power tubes with less than ideal construction standards.

    What is your line voltage?

    I have a set of vintage Siemans tubes in my OEM 70 that have many thousands of hours on them, and still test (and sound) very well.
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    deepee99

    Posts : 2019
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: finally happened-up in flames!

    Post by deepee99 on Tue Oct 09, 2018 9:26 pm

    Red-plating is often a consequence of poor contact between tube pin and socket. It can't be emphasized enough, RETENSION and clean your sockets after a tube change, and make sure the pins are corrosion-free.
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    bluemeanies

    Posts : 259
    Join date : 2015-02-09
    Age : 68
    Location : Folsom Pa.

    Re: finally happened-up in flames!

    Post by bluemeanies on Wed Oct 10, 2018 4:55 am

    I have had one power tube smoke up over the last four years and I know it was me not paying attention.
    I had just turned on the m125's and my daughter called needing information where I had to leave my dedicated room. I was on the phone with her for about 20minutes. Hanging up I realized the valves were still warming up. When I went into the room I smelled smoke and seen smoke disapating from one of my m125's and the room smelled pretty bad.
    I quickly turned both m125's off and begin to research the problem which was me not checking the bias causes an output tube to be lost.
    I live in an area where voltage spikes and lows happen often and regularly. Hence I purchase a kil-o-watt and a Variac. Since, I have never had a problem.

    Do the self bias change with the spikes in line voltage on a regular basis? Is that the intent of how it works? My voltage varies throughout the day and night even readings on weekends are crazy...I have had readings as high as 127 and as low as 115.
    In essence that self bias application would be working overtime in my system.
    Perhaps giving me more problems.

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