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    Red Plated?

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    5/35

    Posts : 12
    Join date : 2014-03-01
    Location : Friday Harbor WA

    Red Plated?

    Post by 5/35 on Fri Mar 18, 2016 8:37 am

    While listening last night, I dozed off. O.K. It was drooling REM sleep, regardless I awoke to the most god awful screeching, rising in both volume and pitch. I spent no time evaluating, I just started flipping switches. The offending noise was coming from the left channel of my M-125's. As things settled, I noticed both of the right side output tubes were glowing brighter than normal and left me with the impression of being very hot.
    Two new tubes are on there way, but have no idea what to check. If I have been paying attention,unwanted noise usually comes from driver tubes. Some problem on the board?
    Any help will be appreciated.

    Dave_in_Va

    Posts : 144
    Join date : 2013-04-02

    Re: Red Plated?

    Post by Dave_in_Va on Fri Mar 18, 2016 10:01 am

    I'm not a tech and there are other guys here who know alot more about this stuff but..

    One day I noticed that my stereo (VTA ST70...SP/PH10) didn't sound right (no howling - just sounded bad) so I checked the bias that had been set a 40mA. All were around double that. I pulled the rectifier (a real Mullard 5AR4), tested it on my tube tester and it was gone. Replaced the rectifier and all has been well for months.

    Bob Latino
    Admin

    Posts : 2415
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Red Plated?

    Post by Bob Latino on Fri Mar 18, 2016 10:33 am

    5/35 wrote:While listening last night, I dozed off. O.K. It was drooling REM sleep, regardless I awoke to the most god awful screeching, rising in both volume and pitch. I spent no time evaluating, I just started flipping switches. The offending noise was coming from the left channel of my M-125's. As things settled, I noticed both of the right side output tubes were glowing brighter than normal and left me with the impression of being very hot.
    Two new tubes are on there way, but have no idea what to check. If I have been paying attention,unwanted noise usually comes from driver tubes. Some problem on the board?
    Any help will be appreciated.

    The most likely scenario for a problem like that is that ONE of those two output tubes on the right side went bad with a dead short (more likely) or a partial short. Since these two output tubes are "teamed up" together, it is possible that the bad tube also affected the other tube it is teamed with. I would say that one or both of the output tubes on that side is bad.

    Try this - Pull two output tubes from the other amp and place them in those two right side positions and see if that amp plays OK now .. If it does get two new output tubes for the right side of that amp.

    Bob

    5/35

    Posts : 12
    Join date : 2014-03-01
    Location : Friday Harbor WA

    Re: Red Plated?

    Post by 5/35 on Fri Mar 18, 2016 11:36 am

    Bob

    Simply put, You're great.

    Thanks

    tubed1

    Posts : 17
    Join date : 2012-01-03

    Re: Red Plated?

    Post by tubed1 on Fri Mar 18, 2016 7:25 pm

    I have in a second system, a CJ MV-50 that was consistently red-plating tubes, and then I came across this must read thread from Jim McShane:

    http://www.audioasylum.com/audio/tubes/messages/26/266372.html

    Problem solved!  Jim McShane you are awesome!

    If for some other unknown reason this is not a solution you may have a bias problem.

    deepee99

    Posts : 1337
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Red Plated?

    Post by deepee99 on Sat Mar 19, 2016 11:55 am

    McShane's advice is always spot-on.
    I took a micrometer to the pins on Russian tubes (KT-88s and KT-120s) and compared the measurements to NOS Tung-Sol 6550s. In ever single case, the 6550s' pins were just a bit skinnier than the new Russians, which red-plated one of the old stock. So if you're going from the New Sensors to some older tubes socket retensioning is essential.

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