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    Less stress on 5AR4/GZ34?

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    Hauge

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    Join date : 2010-07-05
    Age : 50
    Location : Denmark

    Less stress on 5AR4/GZ34?

    Post by Hauge on Sat May 13, 2017 6:48 am

    Was just having a idea.
    What if a silisium diode, like say UF4007, was put in series with the anodes of the 5AR4?
    Has that been tried? - And if. What result?
    Thinking the advantages of the diode, and the tube, combined...
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    arledgsc

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    Join date : 2012-11-30
    Location : SF Bay CA

    Re: Less stress on 5AR4/GZ34?

    Post by arledgsc on Sat May 13, 2017 10:41 am

    The diodes, in series with the HV AC, are the same as having the documented "diode mod".  They do protect the tube rectifier in brown/ blackout conditions of having the input AC power shutoff abruptly.  In this condition the power supply caps are fully charged but 0V AC volts creating an inverse voltage across the rectifier where the cathode is positively charged (filter caps) and anode is negatively charged.  This can cause "flashover" and ruin the tube rectifier.  The diodes in series with tube rectifier increases peak inverse voltage rating of the circuit of an additional 1KV which prevents flashover and conduction of the tube rectifier in the opposite direct than intended.

    Check out the diode mod sticky....
    http://dynacotubeaudio.forumotion.com/t1006-tube-rectifier-diode-mod
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    Hauge

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    Join date : 2010-07-05
    Age : 50
    Location : Denmark

    Re: Less stress on 5AR4/GZ34?

    Post by Hauge on Sat May 13, 2017 2:32 pm

    Thank you very much for your answer arledgsc! Sorry i didn't have focus on the quoted tread...
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    sKiZo

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    Location : Michigan USA

    Re: Less stress on 5AR4/GZ34?

    Post by sKiZo on Sat May 13, 2017 3:25 pm

    Yup ... highly recommended, either during a build or as a retrofit.

    Simplicity itself too, requiring no additional parts except the diodes, and using available unused socket connections.



    I also recommend the addition of a thermistor to the main AC line in. This cuts inrush current that can also damage the delicates over time. Only caveat there is a thermistor never opens completely and you can expect 1-2% drop in your B+, which I suppose could be a problem on an older unit that's already operating on the low side of the range. That's what they make VOMs for, eh. ;-}
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    arledgsc

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    Re: Less stress on 5AR4/GZ34?

    Post by arledgsc on Sat May 13, 2017 3:44 pm

    You are very welcome!..  Flashover usually happens when incoming power flickers or on/off/on/off in quick secession.  The rectifier cathode looses heat and it's inverse voltage holdoff plummets.  That's when the yellow sheet mod diodes come into play.

    The time delay relay offers additional protection as well.  Besides delay of HV supply start up the TDR relay opens quickly on power failures.  This prevents a current path back through the transformer during a flashover prone event.

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