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Thread: Hot transformers on valve amps

  1. #1
    Join Date: Apr 2016

    Location: Bishops Stortford

    Posts: 476
    I'm Chris.

    Default Hot transformers on valve amps

    I have owned valve amps where mains and output tranny get very hot and others where they run cool. What is it about the design that makes this happen?

  2. #2
    Join Date: Oct 2012

    Location: The Black Country

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    I'm Alan.

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    With the hot ones it could be that they are being used close to their loading limits. The design of a transformer usually allows for a 60 degree rise in temperature above ambient.
    It is also dependent on the quality of the steel used for the laminations, better steel result in lower eddy current losses, and reduced temperature rise.


  3. #3
    Join Date: Feb 2013

    Location: W Lothian

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    I'm Grant.

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    Never had any get that hot. warm maybe but not hot
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  4. #4
    Join Date: Oct 2016

    Location: Bolton, England

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    I'm Andrew.

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    A perfect transformer wouldn't dissipate any power and wouldn't get hot at all, but in the real world copper windings have resistance that does dissipate power and current flows within the core and dissipates power. The more current that is being drawn from the secondary windings, the more power is dissipated by the non-ideal transformer elements. The valve heaters take a lot of current, so the more vales there are the more heat is dissipated in the transformers. Also, of course, the valve heaters are getting hot (the clue is in the name ) and that heat often travels through the chassis and into the transformers by conduction.
    Having huge transformers with thick wire helps a lot to keep them cool.

  5. #5
    Join Date: Oct 2014

    Location: SE London

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    I'm Richie.

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    Can I hijack this thread, please?

    I have been listening to music all day (DAC > Croft Vitale > firebottle air > tannoy eaton) and the power has just gone and the CB has tripped. I switched it back on and the Croft is dead. No power light, the transformer is roasting and it smells bad.

    Could the amp have cause the power to go, or has the power cut caused he amp to die?

    Can someone help? I have no idea about electrics!

  6. #6
    Join Date: Oct 2012

    Location: NE England

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    I'm Jez.

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    Quote Originally Posted by martian sunrise View Post
    Can I hijack this thread, please?

    I have been listening to music all day (DAC > Croft Vitale > firebottle air > tannoy eaton) and the power has just gone and the CB has tripped. I switched it back on and the Croft is dead. No power light, the transformer is roasting and it smells bad.

    Could the amp have cause the power to go, or has the power cut caused he amp to die?

    Can someone help? I have no idea about electrics!
    If the transformer has failed or a failure elsewhere has caused the transformer to fail then yes it can get very hot indeed and eventually go short circuit and blow the fuse and/or breaker. We're talking well over 100C hot here.... It was common problem with MF MA50 monoblocks and to a lesser extent with the A1 but they not only ran very hot anyway but also ran the transformer at the limit (or a bit more) of it's ratings.... Molten plastic where the plastic insulating tape was wound around the toroid was the norm.

    Replace the fuse/s remembering probably a 20mm one in IEC inlet and switch it on. If the fuse and/or breaker immediately trips then it is very likely the transformer if it was getting smelly hot... I would not expect something like your Croft to tax the transformer anywhere near that extent so if it is the transformer then it's probably a random failure or a failure of another part which has put an overload on it.

  7. #7
    Join Date: Oct 2014

    Location: SE London

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    I'm Richie.

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    Great - thanks Jez.

  8. #8
    Join Date: Oct 2014

    Location: SE London

    Posts: 299
    I'm Richie.

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    Ive checked the fuse in the amp and it does not look blown. However, with only the kettle lead in the amp (nothing else!) when I turn it on/off, there's a clicking in the speakers. What the dickens is this sorcery?

  9. #9
    Join Date: Feb 2008

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    I'm NotTakingLifeTooSeriouslyTheseDays.

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    What about the fuse in the plug itself, have you checked to see if that one has failed ?
    Quote Originally Posted by martian sunrise View Post
    Ive checked the fuse in the amp and it does not look blown. However, with only the kettle lead in the amp (nothing else!) when I turn it on/off, there's a clicking in the speakers. What the dickens is this sorcery?
    "Today scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality"
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  10. #10
    Join Date: Oct 2014

    Location: SE London

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    I'm Richie.

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    that is next on the list! it is difficult to get to, so I will need to do when I have the patience this evening.

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