Where and when does an amp get hot?

Discussion in 'Amp Tech Center' started by peteb, Jun 1, 2019.

  1. peteb

    peteb Friend of Leo's

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    i did some measuring today using my wavetek meterman 35XP DMM with thermo couple attachment.


    I measured the temperature at various places every 5 minutes for 30 minutes.



    My findings, measurements to follow, are that the amp circuit does not get very hot, most of the worst heat happens in the first ten minutes, maybe with the exception of the cathode resistor and PT which will continue to get hotter.




    Most of the circuit stays below 80 or at least below 90 degrees F. The rectifier tube pins show the most heat and then the power tube. This is a champ amp. The power tube glass gets hotter than the rectifier tube and the cathode resistor stays hotter than the power resistors.




    The hottest place on the amp circuit is pin 8 of the rectifier tube. In 5 minutes it is 144 F and basically stays there. Pin 2 of the rectifier is lower, reaching 100 F after one half hour.


    All of the power tube pins, 2,3,4,5,8 gradually rise up to 100 F. Pin 8 gets the hottest, 130 F after a half hour.


    Pre amp pins stay below 90.


    The pilot light and power switch stay below 80 F.



    The glass goes up to 150-170 F.



    One odd result, the chassis by the PT did not get warm as fast as the opposite end of the chassis, by about 5 degrees.


    The OT peaked out at 80 F after 30 minutes, with no signal.



    I will try later with signal, see how hot things get after 1 hour, maybe 2 hours as well.
     
  2. peteb

    peteb Friend of Leo's

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    EDF73DD0-75E5-44B1-BAD6-41A701B0A601.jpeg
     
  3. rangercaster

    rangercaster Poster Extraordinaire

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    Are you troubleshooting something ???
     
  4. 1300 E Valencia

    1300 E Valencia Friend of Leo's

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    OCD is treatable.
     
  5. JL_LI

    JL_LI Friend of Leo's

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    No it is not! OCD is inherited. I ought to know. It runs in the family. My wife inherited it from her mother and one of our sons inherited it from his mother. OCD takes many forms. My wife is a compulsive shopper. I swear she buys food to throw away so the garbage men shouldn’t be unemployed. We have enough paper towels in the basement to last until we have a second new president. Her mother had canned vegetables where the can rusted out and there was nothing left inside. OK. Sorry. This is a thread about collecting data about where an amp gets hot. That may be something to wonder about, but investigating the phenomenon is certainly not evidence of OCD.
     
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  6. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    That's 100% normal BECAUSE the PT , rectifier and power tubes are closest to that end.

    And everything else the most irrelevant and useless bunch of measurements I've ever seen. Meaningless and a complete waste of time.
     
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  7. schmee

    schmee Doctor of Teleocity Silver Supporter

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    You've got that backwards.... from what he said.
     
  8. thechad

    thechad Tele-Meister

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    Not sure if it makes a huge difference but were you PLAYING the amp? Or just having it run idle?
    I know I have touched a tube (pre-amp or power tube I can't recall) after playing loud with my band for a couple hours and it was pretty darn hot! It didn't leave a scald mark, but I sure pulled myself away from it quick enough. I guess 166-ish might be about right. Isn't that "hot"?
     
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  9. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    I imagine they would get pretty hot around noon in the middle of the Wahabi Desert.

    You could buy a little fan to cool it down if you are worried about it.
     
    Last edited: Jun 1, 2019
  10. kbold

    kbold Tele-Afflicted Silver Supporter

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    Transformers get warm, tubes get hot. Tube amps have a warm-up time because they sound better when they are warm.

    Thermocouples aren't that accurate. If you get an RTD sensor, you will be able to measure with 0.1 degree accuracy, and greatly relieve your OCD.
     
  11. kbold

    kbold Tele-Afflicted Silver Supporter

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    I was going to recommend playing outside in the middle of summer, but didn't want to sound tooo ... flippant. OCD is a serious affliction.

    Edit: I have read of people wanting to cool their tube amps. This is silly - tube amps need to be hot to sound good.
     
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  12. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    A little cooling can sometimes help. You don't want the amp cooking for real.
     
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  13. Believer

    Believer Tele-Meister

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    I had to put a cooling fan on my DSL 401 to keep the bridge rectifier from de-soldering itself from the board, so yeah, tube amps need to get to a proper operating temperature, but some can get too hot.
     
  14. kbold

    kbold Tele-Afflicted Silver Supporter

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    I've heard that DSL 401's can get too hot. For you, a fan.
    Not to put down Marshall, but this seems to be a design flaw. A properly designed amp should take care of overheating issues before getting to the production stage.
     
  15. MrCairo46

    MrCairo46 Friend of Leo's

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    If
     
  16. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    I was going off his "hottest temperature" description - not the speed at which one side or the other of the chassis warmed up.

    It's still all silly, trivial information. peteb regularly comes up with a deep analysis of some piece of unimportant, irrelevant information, seemingly in the hopes that others will get sucked into the vacuum. Hence the early "OCD" post by someone else....
     
  17. Musekatcher

    Musekatcher Friend of Leo's

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    I've done the same using a pyrometer. I got 160-170F on most of the tubes, some were closer to 130-140F. Transformers cooler but still warm. I thought it might be a good way to later trouble shoot or check the health of things.
     
  18. peteb

    peteb Friend of Leo's

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    Good question. Every thread should have a point!


    It was this thread that got me thinking about amp heat, and that it might be interesting to measure it.



    http://www.tdpri.com/threads/is-this-normal.953272/
     
  19. peteb

    peteb Friend of Leo's

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    The first test above, was done without signal, I was too busy measuring. The second test, done last night, more than three hours, was with signal, which may have played a role in keeping things cool, or not?


    Yeah, 166 F is about right. Another goal of the test was to test thermal measuring. I visited a friend yesterday, in between the tests, and he was smoking ribs. The smoker was at 250F and I used the feel of that as a gauge. I have felt some hot power transformers in the past, (the main reason I don’t like to leave an amp on more than a couple few hours) and I was estimating a hot PT might approach 200 F but probably never get as high as 250 F.
     
  20. peteb

    peteb Friend of Leo's

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    I was thinking about that. My ambient temperature was in the mid 60s and most of the circuitry stayed below 100 degrees F for three hours. I realize it is entirely possible to turn an amp on that is already over 100 degrees F.
     
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