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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    The benefit of space

    corndog71
    corndog71
    corndog71


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    • Post n°1

    The benefit of space Empty The benefit of space

    Post by corndog71 Mon Oct 26, 2015 10:59 am

    I finally got an infrared thermometer and tested it out on my amp.

    Ambient temperature was somewhere between 80-84 degrees.  (I forgot to get the exact temp)

    After around 75 minutes warm up time here's what I got.

    https://s576.photobucket.com/user/corndog642/media/VTA%20ST120/IMG_8733_zps764f64ee_2.jpg.html?sort=3&o=5

    It's interesting to note the lower temps on the right channel.  I know that far right tube is going bad as I can't get the bias lower than 0.65VDC.  I think it's dragging the 3rd tube down with it too. Crying or Very sad   At least the left channel is still holding up strong.


    Last edited by corndog71 on Wed Aug 23, 2017 4:59 pm; edited 2 times in total
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    GreggW
    GreggW
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    • Post n°2

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    Post by GreggW Mon Oct 26, 2015 12:35 pm

    With the extra real estate, your power tubes run 70-100 degrees cooler than mine. What rectifier do you use?
    I guess tube temperature isn't too critical, because, my oh my, the music sounds so good...
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    corndog71
    corndog71
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    • Post n°3

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    Post by corndog71 Mon Oct 26, 2015 1:26 pm

    GreggW wrote:With the extra real estate, your power tubes run 70-100 degrees cooler than mine. What rectifier do you use?
    I guess tube temperature isn't too critical, because, my oh my, the music sounds so good...

    UF4007
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    sKiZo
    sKiZo
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    • Post n°4

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    Post by sKiZo Mon Oct 26, 2015 8:38 pm

    I win? I was told there'd be cookies?

    The benefit of space Tube-temps

    About an hour on standby, ambient temp is 68F ... yes, I am a cheap basterd when it comes to heating the house.

    Anyway, my plan seems to have worked. One of the primary objectives when laying out and ventilating the chassis was to provide breathing room for the tubes. Chimney effect, what with cooler air being drawn up from under the chassis plate as the tubes heat, is certainly doing it's thang as evidenced by this test. One advantage of the taller rectifier and increased chassis ventilation seems to be keeping the heat off the iron as well ... I didn't bother posting temps on the sides facing the tubes, as there's basically no difference. Not seen is the increased gap between the transformer bodies and plate ... I made the holes as large as I could and still have enough metal to tie them down properly. Ditto on the driver tubes ... I could have gone a couple mm's larger on the holes to increase the gap, but what I got seems to be working well.

    Worth mentioning, the lower temps on the right bank were a bit of a headscratcher, then I realized that's more than likely courtesy of the Eico HF12A mono amp that sits right next to the ST120. I use that to drive the center channel here. That puts out quite a bit of heat as well, what with 7 tubes cooking away in that one. You'd think that would INCREASE the heat on the right side of the ST120, but once again, chimney effect comes into play. The Eico pulls enough air that it helps cool the ST120?

    The multi-cap is tucked under the chassis plate, and is just barely above ambient temp.

    * I just used the temp probe that came with my Tenma meter ... no telling how accurate that is. Best I can say is, it was right on the money for ambient temp compared to the wall thermostat ...

    Oh. The tubes tested might make a difference ...

    Power - TAD KT88STR
    Rectifier - Mullard GZ-37
    Center driver - 5363
    Channel drivers - TAD 12AU7A

    Be interesting to compare temps with the KT120's installed, but I'm too lazy to switch right now ...

    PS ... those TAD KT88STR's have broken in right nice. Very sweet and full. Maybe not as much bottom as the KT120s, but I can compensate with a slight tweak of the dbx boom box.
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    corndog71
    corndog71
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    • Post n°5

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    Post by corndog71 Mon Oct 26, 2015 10:07 pm

    Hmmm... well played, my friend. Well played indeed.

    Until next time. Twisted Evil
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    GreggW
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    • Post n°6

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    Post by GreggW Mon Oct 26, 2015 10:38 pm

    Very nice work by both of you...
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    sKiZo
    sKiZo
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    • Post n°7

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    Post by sKiZo Tue Oct 27, 2015 12:33 am

    corndog71 wrote:Hmmm...  well played, my friend.  Well played indeed.  

    Until next time. Twisted Evil

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    deepee99
    deepee99
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    • Post n°8

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    Post by deepee99 Tue Oct 27, 2015 12:01 pm

    Space: The final frontier. I remember Supreme Allied Commander Bob L's advice from years aback, to paraphrase: Let your tubes and transformers stare at the ceiling, not at the shelf above.

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    corndog71
    corndog71
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    • Post n°9

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    Post by corndog71 Tue Oct 27, 2015 4:34 pm

    Ok, so I didn't write down the temps at the time for the first pic and went on memory.scratch So I ran the amp for around 5 hours before checking again. This time I wrote them down.

    The benefit of space IMG_8733_zps764f64ee_2
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    Kentley
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    • Post n°10

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    Post by Kentley Tue Oct 27, 2015 5:05 pm

    Before we get too excited, let's remember that temps AT FULL GALLOP are likely to be quite a bit higher than temps at IDLE. Perhaps we should require temps to be registered after playing Metallica at bone-crunching volume for an hour. Then we'll separate the men {with bleeding eardrums} from the boys {with blistering sores}.
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    corndog71
    corndog71
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    • Post n°11

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    Post by corndog71 Tue Oct 27, 2015 5:18 pm

    Kentley wrote:Before we get too excited, let's remember that temps AT FULL GALLOP are likely to be quite a bit higher than temps at IDLE. Perhaps we should require temps to be registered after playing Metallica at bone-crunching volume for an hour. Then we'll separate the men {with bleeding eardrums} from the boys {with blistering sores}.

    Unfortunately, I have neighbors and a twitchy girlfriend to contend with. Otherwise I would totally try that.

    In the meantime I have a bunch of holes to drill.
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    Kentley
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    • Post n°12

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    Post by Kentley Tue Oct 27, 2015 5:21 pm

    corndog71 wrote:Unfortunately, I have neighbors and a twitchy girlfriend to contend with.  Otherwise I would totally try that.

    In the meantime I have a bunch of holes to drill.

    rendeer lol!
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    deepee99
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    • Post n°13

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    Post by deepee99 Tue Oct 27, 2015 5:22 pm

    Is the house on fire? What is that red thing on your M-125? Honey, what is that glow and nasty smell? Why are those sirens sounding so close? We need to buy sand amps and move to a trailer park.
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    sKiZo
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    • Post n°14

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    Post by sKiZo Tue Oct 27, 2015 7:51 pm

    corndog71 wrote:

    Unfortunately, I have neighbors and a twitchy girlfriend to contend with.  Otherwise I would totally try that.

    In the meantime I have a bunch of holes to drill.

    Should be an interesting experiment. I drilled my chassis (well, FPE did) right from the start, so no A/B comparison available.

    Don't forget to vent the bottom! That cool air has to come in somewhere! Mine has a cheese grate bottom on it. Neat stuff cut in various sizes for custom truck grills ... got it offa da bay.

    The benefit of space S-l500

    You can bend it too. I cut a couple pieces of scrap 1x4 for the angle I wanted, then just compressed the metal between the two pieces with a couple C clamps. It'll want to spring back a little, so just cut the angle a bit sharper than you want for the final piece.

    PS ... I wouldn't lose any sleep over the temps you're seeing. Seems to be pretty much ballpark on a typical amp.
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    corndog71
    corndog71
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    • Post n°15

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    Post by corndog71 Tue Oct 27, 2015 10:15 pm

    sKiZo wrote:PS ... I wouldn't lose any sleep over the temps you're seeing. Seems to be pretty much ballpark on a typical amp.

    I won't. But I'm in between projects right now and drilling holes is always fun. bounce
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    sKiZo
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    • Post n°16

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    Post by sKiZo Tue Oct 27, 2015 10:44 pm

    ... I suppose I'll be to blame if it all goes horribly wrong ... clown

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