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Should Mesa 400 P/T be hot in standby?

Discussion in 'Amps and Cabs [BG]' started by eshalon, Oct 29, 2013.


  1. eshalon

    eshalon

    Sep 4, 2008
    New Zealand
    Just a quick question. Had been playing my Mesa 400 non plus before flicking it to standby and reading tb forums for about half an hour and decided I would try the 12U7 swap again. Took the lid of and the preamp tube was still really warm. So were the power tubes and the power transformer (i think. The one on the left when looking from front) was quite hot. I havn't noticed this before and just wondering if this is normal or not?
     
  2. You have to fully power the amp down if you want to try changing tubes. In standby all the tube heaters are still being kept hot. The biggest power draw on the Power Transformer is the tube heaters so I could understand it still being warm, not only due to the load but all those nice hot heaters in there.
     
  3. eshalon

    eshalon

    Sep 4, 2008
    New Zealand
    Sorry I did power it down before trying to change the tube but it still felt hotter then What I thought they normally were. Felt more like full operating temp. Would the power transformer be hot from that? not just warm but reasonably hot?
     
  4. eshalon

    eshalon

    Sep 4, 2008
    New Zealand
    OK and it's been powered down now for 10-15 mins and tubes have cooled down but p/t still feels more or less the same temp
     
  5. It is a BIG piece of iron in there, that will take some time to cool off.

    PT's are usually rated 65 to 85 degrees C max operating temp.
     
  6. eshalon

    eshalon

    Sep 4, 2008
    New Zealand
    Ok it might be fine I've just never noticed it to be that hot before. And didn't remember the tubes being that warm when I've done the swap before. Thanks for your help B-string
     
  7. No problem, by the way do not ever try changing the power tubes shortly after you have played. The bulb temp is usually around 270 degrees F, 133 C
     
  8. eshalon

    eshalon

    Sep 4, 2008
    New Zealand
    Oh no I won't it was a preamp tube I was changing
     
  9. Them either. Their heaters get to the same temp as the big tubes do; they're just smaller. They cool faster but they'll still sizzle your fingers if you try it too soon. Done it.

    New Sensor (EHX) sells a cool little foam rubber dealio called the "tube glove." The thing is a godsend for taking out hot tubes... beats the crap out of wrapping a towel around your hand.
     
  10. eshalon

    eshalon

    Sep 4, 2008
    New Zealand
    Thanks, but i wait untill they are cool enough. I'm really liking the 12au7 now. Didn't seem to like it so much the first time I tried it. Getting a lot more clarity now, although I did enjoy some of that drive I had before
     
  11. top028

    top028

    Dec 14, 1999
    Lancaster, PA
    I am digging up a thread, but I just picked up one of these guys. I am used to my fenders running cucumber cold all day in the sun, so I was alarmed when I dug inside after playing for about an hour. I was rolling tubes around, and I found the same problem. The power transformer was HOT. like 110 deg hot. The amp sounds great with stock power tubes from mesa. By the way I do like the 12au driver! I also like an AT in the V2 (second from right) it gives the EQ section a little more head room and allows a better range of grit.
     

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