Hiwatt V1 12ax7 blowing

Discussion in 'Amp Tech Center' started by DucDone, Sep 25, 2021.

  1. DucDone

    DucDone Tele-Meister

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    Hi. I am building a Hiwatt dr103, and I've been trying to get it to work. What's puzzling me now is that the V1 tube has blown twice, and I can't figure out why. Any suggestion why that could be, what could cause a 12ax7 tube to blowe? (See pic)
     

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  2. VintageSG

    VintageSG Friend of Leo's Silver Supporter

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    That's mechanical, not electrical. The white is the getter flash reacting to the air.
    Is the socket really, really tight when fitting the valve?. Soldering to the socket pins is best done with a socket-saver or old valve you care naught for as it keeps the socket in line and alerts you to flowed solder by soldering the saver/valve into the socket :)
    Solder runs that cause tightness in the socket can lead to excessive force being used to fit the valve, but failures tend to be around the pin area, not the body. That's usually heavy handling.
    Electrical issues rarely cause the getter to ghost out.
    Are you using a shield?, are you using Sino valves, ie, Shuguang ( they're sometimes very thin glass and fragile as a result, but even so... )
    If you bought the valves as a job lot, you -may- have a physically weak batch and rough housing them is causing the issues.

    Sometimes, crap just happens.
     
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  3. Jon Snell

    Jon Snell Tele-Holic

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    Rough handling is all that can cause that.
     
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  4. slider313

    slider313 Tele-Afflicted

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    Are they RFT ECC83's? If they are, the glass is thin and the pins are not as robust as most other 12ax7 types. It is very common with this brand.
     
  5. NTC

    NTC Tele-Holic

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    Does the amp work for a while first? If so, one could replace the tube with an expendable tube and look to see if one of the plates turns red before the glass cracks. The overheating could cause the glass to crack. However, what the others have said is more likely.
     
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