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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    That’s right, and that’s where this is all going. How hot does the curcuit get, and what does solder do at that temperature?


    I looked it up yesterday. Solder melts at 300 something degrees F. What I’m seeing is that the circuit temp stays well below 300 F, unless ? Happens?



    What about AC versus DC? I was told that AC is not to be soldered, for this very reason. I saw yesterday that the AC circuit, the wall circuit, stays cool.
     
  2. peteb

    peteb Friend of Leo's

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    True, trannies get warm, and tubes get hot but I am interested in the temp of the circuit itself, and the circuit connections.


    Thermo couples may not be that accurate, that was my first experience and I was testing it out. It seemed to work pretty good, pretty fast. Another thing that peaked my interest in this technology is that I gave blood this week and they measured my temperature from a distance of about 1 inch.


    My meter has two settings, 400F and 1832 F. I quickly disregarded the 400 F setting because it gave me the first decimal point and the 1832 setting did not. I had no interest in the decimal point.
     
  3. peteb

    peteb Friend of Leo's

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    Thanks for the confirmation that it is something worth looking at.


    What I see is that circuit elements exceeding 150 degrees F are out of the ordinary and may be a ‘signal’ that something is wrong, getting too hot.
     
  4. thechad

    thechad Tele-Meister

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    Ummm :confused: pretty much the whole circuit in the amp is running AC, not just the part that plugs in the wall. The DC part of the amp is after your rectifier/B+ voltage supply. It would be rather difficult to make a guitar amp and not solder any AC signal lines....
     
  5. peteb

    peteb Friend of Leo's

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    Test results up to 3 hours and 15 minutes, under normal playing conditions:


    The amp did not really continue to heat up. Most of the circuit stays at or below 100 degrees F.


    The main exceptions:

    The cathode resistor continued to get hotter, reaching 140 degrees F.

    Pin four on the rectifier is the hottest place in the circuit. Five minutes into the test it measured 144 F, as it did after 10 min, 15 min, 30 min, 2 hours, and 3+ hours.



    Thank you for reading and the feedback.




    64E0D355-33E3-4B5E-8588-5D13CE60296F.jpeg
     
  6. peteb

    peteb Friend of Leo's

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    The current and the power in the AC circuit powering the amp are much larger than in the AC circuit that is the output of the amp.
     
  7. radiocaster

    radiocaster Poster Extraordinaire

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    Maybe, but kind of fun.

    You could say the same about playing guitar.
     
  8. telemnemonics

    telemnemonics Telefied Ad Free Member

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    For me the hottest part is usually where the smoke is coming out.

    After the amp cools down I can still find the hot part because it's charred and half gone!

    I do like to grab a hot PT when I'm bored.
     
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  9. Musekatcher

    Musekatcher Friend of Leo's

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    This amp was built and biased in the Shoals by a pretty knowledgeable guy. Its biased hot, on purpose I would assume. It does everything really well, and its still my favorite, among several tube amps. Whatever temps its operating at, is the *right* temp, based on that. The vintage tubes (probably only set this amp has seen, maybe four years old) have lasted a year of gigging so far, still quiet, still creamy. Hot bias probably shortens tube life, but I'm good with it. I've got some ANOS replacements waiting when one or more tubes flake out. I count myself lucky.
     
  10. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    You're avoiding mentioning the real problem here....Amplifiers are prone to hypothermia, and need covering warmly.

    upload_2019-6-2_20-47-27.png

    upload_2019-6-2_20-51-2.png
     
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  11. kbold

    kbold Tele-Afflicted Silver Supporter

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    If you want to go high tech, THE best piece of fault testing equipment is a thermal imaging camera. This will give you a thermal picture of any and all hotspots in the circuit.
    They're a bit expensive though.
     
  12. peteb

    peteb Friend of Leo's

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    Good points Kbold. Thermal imaging is infrared. I use IR for detection, a little.






    I’m noting the obvious conclusions.


    The most heat is in the thermionic action inside the tube.



    After that the rectifier is second hottest followed closely by the Cathode and then the plate of the power tube.



    The pre amp stays cool. The input side of the PT stays cool, and the OT.


    Heat will continue to build up in cathode resistors and the PT.


    a question




    Do heat related problems occur in the pre amp even though it says relatively cool?
     
    Last edited: Jun 2, 2019
  13. kbold

    kbold Tele-Afflicted Silver Supporter

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    You wouldn't expect thermal problems in preamp stage.

    Lots of good observations/conclusions you've made.
     
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