Tube warm up time technical measurements

Discussion in 'Portable and Other Gear Measurements' started by atomicbob, Jan 27, 2017.

  1. atomicbob

    atomicbob dScope Yoda

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    Not sure I understand what happened here. I do remember a day when I had been acquiring many microphones in rapid succession for the studio and the better half warned me to slow down or I'd be sporting one applied as indicated in posts above. Bad day to have a Soundelux U95S arrive.

    *edit*
    Dimensions 271mm length x 52mm maximum diameter.
     
    Last edited: Apr 6, 2018
  2. Azimuth

    Azimuth FKA rtaylor76, Friend

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    Still not as big as a U47 tube.

    PVC diaphragm is the real deal.

    Still, how about an M1 bottle?
     
  3. atomicbob

    atomicbob dScope Yoda

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    @gixxerwimp @msommers See post #2 for SW51+ update
     
    Last edited: Jun 9, 2020
  4. gixxerwimp

    gixxerwimp Professional tricycle rider

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    It wasn't me who asked, but thanks anyway! :bow:
     
  5. atomicbob

    atomicbob dScope Yoda

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    Aw, I hate it when I have a senior moment like that ... you are correct of course.

    16 hr days supporting corporate needs, which support medical front liners, when I should be at least semi-retired is taking a bit of a mental toll.
     
    Last edited: Jun 9, 2020
  6. gixxerwimp

    gixxerwimp Professional tricycle rider

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    That's OK, but at some point in the future I'll be asking about measurements for those SW51 tubes I sent you ;)

    Keep fighting the good fight! |\/|
     
  7. atomicbob

    atomicbob dScope Yoda

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  8. atomicbob

    atomicbob dScope Yoda

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  9. winders

    winders boomer

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    I know it doesn't really matter, but have you measured how an amp performs as the tubes warm up? How warm do the tubes need to be for the amp to reach its nominal state?
     
  10. atomicbob

    atomicbob dScope Yoda

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    20210928 Studio B Genalex 300B warmup time series

    I created a dScope script to collect data over a period of time at one minute intervals.

    Periods measured:
    1. t=1 to 10 minutes
    2. t=30 to 34 minutes

    Measurements:
    1. 1 KHz 0 dBu spectrum 32K FFT, approximately 5 seconds sample time
    2. residual noise spectrum 64K FFT, approximately 10 seconds sample time

    Setup conditions:
    Studio B volume set to unity gain
    300R load

    Spectrum measurements are single FFT snapshots, NOT averaged. A single FFT snapshot is obtained to minimize the sample time.

    Each animation will pause on the first measurement in the series for 2 seconds then proceed at one measurement per second.

    1 KHz spectrum 0 dBu, t=1 to 10
    20210927 Studio B Genalex 300B L ch dist t1-t10.gif

    1 KHz spectrum 0 dBu, t=30 to 34
    20210927 Studio B Genalex 300B L ch dist t30-t34.gif

    residual noise spectrum, t=1 to 10
    20210927 Studio B Genalex 300B L ch noise t1-t10.gif

    residual noise spectrum, t=30 to 34
    20210927 Studio B Genalex 300B L ch noise t30-t34.gif

    During the first 10 minutes spectrum and noise undergoes considerable change.
    The measurements indicate changes settling down at 30 minutes.
     
  11. winders

    winders boomer

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    Thanks for doing that!

    I used to turn on my KT88 tube amp (2 channel speakers) about 30 minutes prior to listening. But now, more often than not, I just turn it on and listen within 5 minutes.

    How would you describe what we might hear during the first 10 minutes versus post 30 minutes? While I see a lot changes in the first 10 minutes, most of it happens below db levels that I would expect to make a huge difference in my 35 db ambient noise environment. With headphones I assume the noise may be more of an issue.
     
  12. gixxerwimp

    gixxerwimp Professional tricycle rider

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  13. atomicbob

    atomicbob dScope Yoda

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    Mjolnir 3 is a solid state amp that behaves considerably similar to a tube amp. With that in mind the following data depicts Mjolnir3 warmup time.

    Measurement conditions:

    Room ambient temp: 68 °F / °20 C
    OS136 IR sensor located 6 inches above Mjolnir3 heat sink
    Spot size 1 inch centered on back heat sink
    Mjolnir3 in NFB off mode
    Mjolnir3 set for high gain

    Measurement setup:
    Mjolnir temp warmup time small.jpg

    Data:
    20230923_Mjolnir3_OS136_C annotated_cropped.png


    20230923_Mjolnir3_OS136_F annotated_cropped.png

    Full equilibrium is reached at approximately 50 minutes

    Congested sound begins to dissipate at approximately 20 minutes and is mostly gone around 30 minutes.
    Note the little plateaus during the first 30 minutes. There are multiple thermal inertias to overcome.
     
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  14. Vansen

    Vansen Gear Master (retiring)

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    Interesting. Your MJ3 runs colder than mine. After 30 mins, mine is 165 degrees F with my FLIR. When I set a type-k thermocouple on the fins without thermally bonding it to the heat sink I get about 158 degrees. I don’t trust my FLIR, but the un-bonded type-k seems to show it’s not too far off.

    (I’d have bonded it, but looks like I left all of that stuff at work.)
     
  15. atomicbob

    atomicbob dScope Yoda

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    what is your ambient temperature?
    mine is a very cool 20 °C
    Also the AC mains come from a UPS and are at 115VAC. If your AC mains are higher there is the possibility your amp runs hotter for that reason. There are no IC voltage regulators in this amp, if I understand correctly.
     
  16. earnmyturns

    earnmyturns Smartest friend

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    Local utility seems to think more V is better, never seen it below 122 V, 124 V right now.
     
  17. Cspirou

    Cspirou They call me Sparky

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    I thought a Class A amp would have a much shorter warmup time. Shows how efficient those heatsinks are
     
  18. Riotvan

    Riotvan Snoofer in the Woofer

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    I have a 20 here that says @schiit will get one back after some doofus does a liquid metal mod for the tim and almost starts a fire.
     
  19. Vansen

    Vansen Gear Master (retiring)

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    My ambient temperature is definitely higher at 23 to 24 degrees. Even in Seattle at this time of year, that’s what my house likes to be at with the AC off. Im running the amp at 115 VAC from a double conversion UPS since my EC amp hums if I go higher.
     
    Last edited: Sep 24, 2023
  20. atomicbob

    atomicbob dScope Yoda

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    Another possible reason my Mjolnir 3 runs cooler is elevation of the amp with feet that raise it by 0.5 inch:
    https://www.amazon.com/dp/B092PN2C3M
    These come with self adhering soft discs with a hole in the center. I put the discs on the top side of the feet. Rubber O rings down, soft disc up.

    Elevation allows more air flow below the amp and also some distance to the component on which it sits
    (Holo Spring 3.)
     

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