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    How hot is hot?

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    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    How hot is hot?

    Post by j beede on Tue Feb 15, 2011 2:32 am

    Anyone have external case temperature data to share for their Mark III power transformer?
    ...j

    quad44

    Posts : 15
    Join date : 2009-06-08

    Re: How hot is hot?

    Post by quad44 on Tue Feb 15, 2011 2:56 pm

    I have the following measurements on my new Dynakitparts Mk3 with the case off and ambient 68deg F. Measurements taken after an hour of operation for the power transformer. Measurements taken with a laser temperature reader.
    Transformer case temperature closest to 5AR4 is 193deg F.
    Case temperature closest to KT 88 is 102deg F.
    Opposite side of transformer(facing out) 77deg F. and 80deg F. for top of transformer(lamination).
    Quad cap temperature close to chassis is 190deg F.
    Hope this helps for your reference.


    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: How hot is hot?

    Post by j beede on Wed Feb 16, 2011 1:55 am

    Thanks for that detail quad44. Something does seem amiss though... the thermal mass of the PT is large and it surprises me to see the large differences in temperature that you are seeing on different parts of the transformer. Mine runs about 115°F and doesn't vary much--maybe 5° across the transformer. I am running some experiments to map PT temperature versus bias setting.
    ...j

    quad44

    Posts : 15
    Join date : 2009-06-08

    Re: How hot is hot?

    Post by quad44 on Wed Feb 16, 2011 2:06 pm

    The only explanation for the variance between the core temperatures and the outside I measure can be explained by the thermal and physical coupling between the transformer cover(s) and the main mass of the transformer.
    The cover(s)and the windings have a layer of air between them and some contact between cover lip and the lamination whilst the windings and the core are about as closely coupled as you can get. I would therefore use the temperature readings of the core as a true indicator on the condition/performance of the transformer.Mine is 80deg.F measured at the top. Where do you measure yours?
    The cover closest to the rectifier reads high because of its near proximity to the rectifier. The reading on the quad cap is consistent with this observation.
    My KT88's are biased at 50ma.I will reprise the test after the Mk3 have been on longer than an hour playing some other music. I also find that there are temperature variations depending on the type of music being played.
    My biggest concern is why the Genalex KT88's smell up my listening area after the system has been on for an hour or so. I have been told that this is normal "burn in".
    Maybe Kevin at Dynakitparts or Bob L can jump in here to provide some guidance.

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: How hot is hot?

    Post by j beede on Wed Feb 16, 2011 4:12 pm

    80°F is very cool, my vintage Mark III PTs run 30-40° hotter than that Sad. 50mA bias? As in 1.12V at the test pin? I used two IR temperature probes (one from Harbor Freight, one from Radio Shack) to measure the exposed areas of the laminations. The covers measure with 5-10° of the lamination temp. My amps seem to stabilize temperature-wise after 2-3 hours of run time. I will use my inductive ammeter to see what my amps draw tonight. Yes, some tubes seem to produce more odor than others. I assume that this is due to the adhesive that is used to attach the envelope to the base. What else is there to emit odor? All my 6550s have metal bases and all of my rectifiers have composite. The Sovtek outputs seem to be less smelly than GE... I think. My "modern" fleawatt 300B amplifier ran blistering hot tubes temperatures--but did not smell at all. It had all Shuguang tubes.

    Bob Latino
    Admin

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

    Re: How hot is hot?

    Post by Bob Latino on Wed Feb 16, 2011 6:49 pm



    Above is a photo that I posted before on another thread. It's not a Mark III but it's my own ST-120 being tested for heat dissipation with the toughest tube that I would run in there - the Tung-Sol KT120. The Tung-Sol KT120 draws more current than any tube that you could plug into the ST-120. Tube amps run HOT - It's a fact. The power transformer will be too hot to touch for more than a few seconds after the amp has been on for a few hours. It's perfectly normal.

    As I said before on another thread, I don't recommend any Dynaco tube amp be put into any cabinet where there is a restriction of air flow. Tube amps should "look at the ceiling" IMHO.

    Bob

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: How hot is hot?

    Post by j beede on Wed Feb 16, 2011 10:28 pm

    Now that is what I call a detailed posting! Thanks. Those numbers are above what I am seeing--which makes sense. I will measure the line current draw later tonight.
    ...j

    quad44

    Posts : 15
    Join date : 2009-06-08

    Re: How hot is hot?

    Post by quad44 on Wed Feb 16, 2011 10:59 pm

    After 3hrs. of playing I measured again and here are the results. The transformer side facing out was 103 deg.F, the top was 122.deg F and the side facing the rectifier was 156 deg F.
    I took hourly measurements during this period and it appears that the average per hour increase was about 4 deg.F for the side and about 11-12 deg F for the top and rectifier side.

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: How hot is hot?

    Post by j beede on Thu Feb 17, 2011 2:05 am

    Thanks for measuring again quad44... Those numbers are closer to the 110-120° that I am seeing on the laminations after a couple hours of running.
    ...j

    Newportcycle

    Posts : 19
    Join date : 2010-09-29
    Location : Central Maine

    Re: How hot is hot?

    Post by Newportcycle on Thu Feb 17, 2011 6:59 am

    Bob, do you belive the 300+ degree readings is the surface temprature?

    Bob Latino
    Admin

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

    Re: How hot is hot?

    Post by Bob Latino on Thu Feb 17, 2011 7:20 am

    Newportcycle wrote:Bob, do you belive the 300+ degree readings is the surface temprature?

    Those 300+ F readings are on the plates of the output tubes which is pretty much normal.

    Bob

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