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    Quad cap temperature

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    GreggW

    Posts : 55
    Join date : 2015-07-15

    Quad cap temperature

    Post by GreggW on Wed Oct 21, 2015 10:01 pm

    Checked the quad cap temp after running the amp at low volume for an hour. I measured 120 an inch from the top and bottom of the cap and over 200 in the middle. (Room temperature is 75.) Just wondering if this is normal....

    sKiZo

    Posts : 1287
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Quad cap temperature

    Post by sKiZo on Wed Oct 21, 2015 11:31 pm

    What amp?

    The quad cap itself shouldn't generate much heat. It's proximity to the iron and tubes that does it. From there, it's all about ambient temperature and air circulation as to how hot it will actually get.

    Bob posted up a pick somewhere around here with test temps of all the components.

    Aha!

    http://dynacotubeaudio.forumotion.com/t828-tube-amps-get-pretty-warm-especially-in-the-summer-photo?highlight=temp

    Notice the difference between the front and rear tubes ... that's due to the rears being sandwiched between the front tube and iron. Not a lot of breathing space. And there's the quad cap, right next to it.

    GreggW

    Posts : 55
    Join date : 2015-07-15

    Re: Quad cap temperature

    Post by GreggW on Thu Oct 22, 2015 1:05 am

    I recall seeing this. The back KT88s run 330 or so, but tonight on a whim, I checked the quad cap a few times with similar results. The 5V3a is the rectifier of choice for now, and I wondered if it had an effect on the quad cap. The ST 120 is 3 ½ years old and has very little time on it. The amp's getting better the more it's used...

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Quad cap temperature

    Post by Bob Latino on Thu Oct 22, 2015 8:50 am

    GreggW wrote:Checked the quad cap temp after running the amp at low volume for an hour. I measured 120 an inch from the top and bottom of the cap and over 200 in the middle. (Room temperature is 75.) Just wondering if this is normal....

    Tube amps do run pretty warm .. The quad cap will give off a lot of heat when the amp is running. Your ambient temperature was also 6 degrees higher (75 F vs 69 F) than when I ran the heat test. It will be more difficult for the amp to give up heat when the ambient temperature is higher. As such, the amp will tend to run warmer. Photo below from the link that sKiZo posted ..

    Bob


    GreggW

    Posts : 55
    Join date : 2015-07-15

    Re: Quad cap temperature

    Post by GreggW on Thu Oct 22, 2015 11:31 am

    Didn't realize how warm the quad cap gets, but sitting right next to a 300+ degree tube makes sense. I was concerned because the amp was at a very low volume....

    sKiZo

    Posts : 1287
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Quad cap temperature

    Post by sKiZo on Thu Oct 22, 2015 6:59 pm

    As I mentioned earlier, the quad cap doesn't so much generate heat, as absorbs it ...

    Mine stays nice and cool mounted underneath.



    GreggW

    Posts : 55
    Join date : 2015-07-15

    Re: Quad cap temperature

    Post by GreggW on Thu Oct 22, 2015 9:13 pm

    You've got a great looking 120 with a little extra room. Have you ever checked the real power out with those KT120 glass pillars?

    Tubes4ever

    Posts : 59
    Join date : 2015-07-14
    Location : Star, Idaho

    Re: Quad cap temperature

    Post by Tubes4ever on Thu Oct 22, 2015 9:16 pm

    GreggW wrote:I recall seeing this. The back KT88s run 330 or so, but tonight on a whim, I checked the quad cap a few times with similar results. The 5V3a is the rectifier of choice for now, and I wondered if it had an effect on the quad cap. The ST 120 is 3 ½ years old and has very little time on it. The amp's getting better the more it's used...

    No. The 5V3a is too far away to effect the quad cap to any great degree.

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