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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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    Heat build up with a ST-70 Cage?

    Robert
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    Robert
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    • Post n°1

    Heat build up with a ST-70 Cage? Empty Heat build up with a ST-70 Cage?

    Post by Robert Sun Feb 08, 2009 12:24 pm

    Here's a question I've always wondered about.

    Having owned a Stereo-35 years ago in college, a PAS-3X and Stereo 150 - I always assumed that it was best to put a fan on my heatsinks of the transistorized gear - to allow it to run cooler. I never removed the cage of the ST-35 - and it worked perfectly for 20-25 years before I finally sold it to a friend who was always begging for the great sound of that amp.

    Recently, I bought a Stereo 70 kit from Bob and it works great - but I wanted a "classic" look so I bought an old Dynakit cage on eBay for $40 and installed it. Now it looks really perfect - and is even brown - not one of the newer black ones.

    Man, does it get warm (OK, hot) on the sides and top near the output tubes. Does anyone know if tubes have a shorter life if they are in an enclosed cage rather than free? And then - what if you put a fan on tubes - would that extend their lives even more??? I mean Dyna sold 1000's of these amps for years with the cages on - so they must not be a horrible thing? On the other hand, my college roommate owned a Harmon-Kardon Citation tube amp and these were exposed from the factory...only decorative caps placed over the transformers.

    Thanks, Rob
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    Bob Latino
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    • Post n°2

    Heat build up with a ST-70 Cage? Empty Re: Heat build up with a ST-70 Cage?

    Post by Bob Latino Sun Feb 08, 2009 1:35 pm

    Hi Rob,

    Glad your ST-70 kit is running well ..

    The purpose of the tube cage is to protect your pets and/or small children from having "access" to the heat from your amp. The amp will always run cooler with the cage off. Remember that although the front, back and top of the tube cage have perforations to allow heat to escape the two SIDES of the tube cage do not. The ST-35 that you mention runs on lower voltages and puts out considerably less heat that the ST-70. The ST-35 has the same 13 inch front as the ST-70 but the solid sides of the ST-35 cage sides are only 5 3/8 by 4 inches. The ST-35 cage has less restriction to air flow than the ST-70 cage. If you feel that the ST-70 runs too hot then I would remove the cage for better air flow unless you have pet or young child issues.

    Two other things. IMHO you should never place a tube amp in any position that restricts normal air flow. Keep it away from walls as much as possible, never place it in any cabinet of sorts and always make sure that the top of the amp "looks at" the ceiling of the room that it is in.

    Another thing that I know does not apply in your case BUT - I see "rebuilt" Dynaco amps for sale on Ebay and Audiogon that have their transformers painted some color other than BLACK. Transformers painted canary yellow, pink (!) etc. Understand that the color BLACK dissipates radiant heat energy much better than any other color. Did you ever notice that nearly all automoblile radiators are painted black? Transformers will always run cooler if they are painted black.

    Bob
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    Robert
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    • Post n°3

    Heat build up with a ST-70 Cage? Empty Heat build-up

    Post by Robert Sun Feb 08, 2009 4:50 pm

    Thanks - good information. And yes, that is true that radiators are 99+% painted black.

    So, I don't have kids (well I do - but they are 22 and 25!) to worry about - but have you ever tried measuring power hot (as in a cage) versus free air flow? That would be interesting IMHO.

    Cheers,

    Rob
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    Heat build up with a ST-70 Cage? Empty Re: Heat build up with a ST-70 Cage?

    Post by Guest Sun Feb 08, 2009 7:43 pm

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    Last edited by PeterCapo on Tue Dec 01, 2020 12:29 pm; edited 1 time in total
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    danf
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    • Post n°5

    Heat build up with a ST-70 Cage? Empty Transformer color is not a significant thermal issue

    Post by danf Sun Feb 15, 2009 11:11 am

    Although a pink or yellow transformer might offend your eyes, transformer paint color is not likely to be a thermal issue. (1) Convection, not radiation or conduction, is the dominant cooling mechanism for Dynaco transformers. For convection, paint color is not an issue, but free air flow as described above is very important. Fans to move the air faster will further improve the situation. (2) Even for radiative heat transfer, the far-infrared characteristics of the paint are what matter, not the optical color. Most paints, except high metal content paints, have similar far infrared properties.
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