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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


5 posters

    Is this "red plating"?

    Tube Nube
    Tube Nube


    Posts : 707
    Join date : 2008-12-06
    Age : 59
    Location : Calgary, AB

    Is this "red plating"? Empty Is this "red plating"?

    Post by Tube Nube Sun Apr 10, 2016 4:31 pm

    While casually listening from another room, it occurred to me that I had been hearing a hum in the music -- I guess I dismissed it as part of the on line music track . . . for a few minutes.

    But thought I'd better check.

    The hum was from the right speaker, and the rear right power tube was glowing. I mean, the entire insides were red hot.

    I shut it down, and took some temperature readings. The other tubes were rocking along (Well, it was jazz that I was actually listening to) at about 156 degrees. The red tube read at 408 degrees.

    I guess it's goose is cooked?
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    audiobill


    Posts : 424
    Join date : 2014-03-13
    Location : Albany, NY

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    Post by audiobill Sun Apr 10, 2016 4:40 pm

    It would appear so.
    Bob Latino
    Bob Latino
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    Location : Massachusetts

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    Post by Bob Latino Sun Apr 10, 2016 4:43 pm

    Tube Nube wrote:While casually listening from another room, it occurred to me that I had been hearing a hum in the music -- I guess I dismissed it as part of the on line music track . . .  for a few minutes.

    But thought I'd better check.

    The hum was from the right speaker, and the rear right power tube was glowing. I mean, the entire insides were red hot.

    I shut it down, and took some temperature readings. The other tubes were rocking along (Well, it was jazz that I was actually listening to) at about 156 degrees. The red tube read at 408 degrees.

    I guess it's goose is cooked?

    Either that tube is bad OR that tube lost its bias. If you place that tube in another socket and it does the same thing, then most likely the tube IS bad. If ANY tube red plates in that socket, then check that the 10 ohm 2 watt bias resistor from pins 1/8 to chassis ground on that socket does measure 10 ohms.

    Bob
    Tube Nube
    Tube Nube


    Posts : 707
    Join date : 2008-12-06
    Age : 59
    Location : Calgary, AB

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    Post by Tube Nube Sun Apr 10, 2016 5:11 pm

    Bob, Thanks so much for that advice! When it's all cooled down, I swap those tubes around check bias, watch and wait.
    Kentley
    Kentley


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    Age : 70
    Location : Worcester, MA

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    Post by Kentley Sun Apr 10, 2016 5:56 pm

    Tube Nube wrote:Bob, Thanks so much for that advice! When it's all cooled down, I swap those tubes around check bias, watch and wait.
    Also, it could be that the socket is not making good contact. This has happened to me recently. Retension, and clean socket contacts and tube pins. It is possible to red-plate a tube without damage to either the bias circuit or to the tube itself - if you are lucky.
    Tube Nube
    Tube Nube


    Posts : 707
    Join date : 2008-12-06
    Age : 59
    Location : Calgary, AB

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    Post by Tube Nube Sun Apr 10, 2016 8:05 pm

    Good idea. Since I'm gonna be taking toobs our any who, it's a good time for some de oxit on my dental brush thingy, and a check of the pin holders!
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    wildiowa


    Posts : 237
    Join date : 2012-03-19

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    Post by wildiowa Mon Apr 11, 2016 3:48 pm

    Asking about red plating reminds me of what the Supreme Court said about pornography...it's extremely hard to define or describe, but you kinda know it when you see it!

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