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    Weber copper cap discoloring?

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    vtshopdog

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    Re: Weber copper cap discoloring?

    Post by vtshopdog on Mon Feb 20, 2017 9:59 pm

    In case anyone cares, polishing the copper surface will negatively impact radiant heat transfer by a factor upwards of 30.  Cut and pasted below are emissivity coefficients for polished and oxidized copper.  Higher number means better heat transfer.  The coefficient is expressed as relative to a theoretical "black body" that has ideal heat transfer.

    Please note this applies to radiant heat transfer (what one feels from glowing coals) not conduction (burnt fingers from touching the coals).  The cap will cool by a combination of radiant and conductive heat transfer.  Painting the cap black will improve things to about .9-something for radiant.

    Cooling improvement from drilling holes to vent the can will probably swamp any differences in color though.

    Copper heated and covered with thick oxide layer 0.78
    Copper Polished 0.023 - 0.052

    I have a couple of these torn apart that I never got around to rebuilding.  I think they are kind of sketchy and delicate inside with two sandcast resistors mounted on a circular PCB shoved lengthwise up in the can.  One should do everything possible to not yank on them while warm as the glue holding can to base gets soft and you can disturb the joint where resistor leads are soldered to PCB.
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    arledgsc

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    Re: Weber copper cap discoloring?

    Post by arledgsc on Tue Feb 21, 2017 12:17 pm

    Tube cooling fins would help take heat away from the Weber body. I always have a gentle breeze (virtually inaudible) fan pointed at the rear of the ST-120 power tranny. Enough air makes its way around the transformer to ventilate the Weber. I used a WZ68 for 3 yrs. and it is still copper colored for the better part.

    I never really liked the idea of power resisters inside the can with the rectifier diodes. But no issues using the WZ68 even biasing the output tubes to .55mA
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    deepee99

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    Re: Weber copper cap discoloring?

    Post by deepee99 on Tue Feb 21, 2017 2:54 pm

    The only real grief the Webers ever gave me was running a <2-ohm speaker load; Maggies and Heils in parallel, each being 4 ohm nominal, so I was probably down in 1 ohm territory some of the time. Don't suppose it did the trannies any good, either. Never had one pop with the Vandies or Tylers.
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    deepee99

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    Re: Weber copper cap discoloring?

    Post by deepee99 on Tue Feb 21, 2017 3:17 pm

    vtshopdog wrote:In case anyone cares, polishing the copper surface will negatively impact radiant heat transfer by a factor upwards of 30.  Cut and pasted below are emissivity coefficients for polished and oxidized copper.  Higher number means better heat transfer.  The coefficient is expressed as relative to a theoretical "black body" that has ideal heat transfer.

    Please note this applies to radiant heat transfer (what one feels from glowing coals) not conduction (burnt fingers from touching the coals).  The cap will cool by a combination of radiant and conductive heat transfer.  Painting the cap black will improve things to about .9-something for radiant.

    Cooling improvement from drilling holes to vent the can will probably swamp any differences in color though.

    Copper heated and covered with thick oxide layer 0.78
    Copper Polished 0.023 - 0.052

    I have a couple of these torn apart that I never got around to rebuilding.  I think they are kind of sketchy and delicate inside with two sandcast resistors mounted on a circular PCB shoved lengthwise up in the can.  One should do everything possible to not yank on them while warm as the glue holding can to base gets soft and you can disturb the joint where resistor leads are soldered to PCB.
    Hey Shopdog, since you've got that hand-dandy chart out, is there a significant difference between gloss and flat black? Am also wondering about interior treatments as well. Thnx, d
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    vtshopdog

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    Re: Weber copper cap discoloring?

    Post by vtshopdog on Tue Feb 21, 2017 5:35 pm

    Flat black will be slightly better than gloss black, but both are pretty good.

    Here is a link to one chart:

    http://www-eng.lbl.gov/~dw/projects/DW4229_LHC_detector_analysis/calculations/emissivity2.pdf


    To me, takeaway here is Weber caps probably operate at the margin of functional range in some instances and difference between polishing it and leaving bare to oxidize when pushed to limit might be difference between component failure or not.

    For interior, very likely the simple conductance will be dominant and color won't matter very much.  All things equal, flat black will be better than polished metallic surfaces.  

    (it's been 30+ years since my last Thermodynamics class, so buyer beware on my spewing here ...)
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    cci1492

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    Re: Weber copper cap discoloring?

    Post by cci1492 on Fri Mar 31, 2017 9:01 am

    I had the bright idea yesterday of pulling the ZW68 so I can polish them. Smallest amount of force and the copper tube popped off leaving the rest still plugged into the octal socket. Trim and molding tool set (Harbor Freight) to pull the rest, without further destruction of something that was working perfectly fine. I had a tested spare, so that's in and working. Being that it's apart now, I'd like to swap the parts that are in there and drill the holes on the copper tube. Those of you that have done this, do you reuse the sockets? I see the sockets are available on ebay from China for cheap but they are the same plastic ones. I'm looking for ceramic male octal sockets but can't find them. Is this worth pursuing or just reuse the old one or maybe just get new plastic sockets?

    TIA
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    Peter W.

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    Re: Weber copper cap discoloring?

    Post by Peter W. on Fri Mar 31, 2017 9:14 am

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    deepee99

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    Re: Weber copper cap discoloring?

    Post by deepee99 on Fri Mar 31, 2017 10:10 am

    Peter W., good hit on the socket-maker. Thanks, and excellent pricing.
    I dunno why they use such weak glue on the copper-caps but the metal cap is there to protect accidental touching of the high-energy components (& presumably for aesthetics), and the weak joint makes it much easier to remove to do the cooling mod. After all, it's not protecting a vacuum. And for $20, whaddya expect? Smile


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    Peter W.

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    Re: Weber copper cap discoloring?

    Post by Peter W. on Fri Mar 31, 2017 10:20 am

    Second that on the cooling mod.

    One would think that as they are punching metal in any case, punching a perforated material would be equally as possible. Not quite the same aesthetic, I guess.

    I am also guessing that they use a pretty basic cyanoacrylate glue during the assembly - fast, cheap and tough, initially. But when heated gets brittle fast.

    NOTE TO ALL:

    DO NOT, ever, use CA glues (AKA: "super glue") for the purposes of re-attaching tube bases to glass tubes. It is almost guaranteed that the glass envelope will fracture at that point some time in the near future. High-temp electronic silicon is the better choice (no acetic acid).
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    cci1492

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    Re: Weber copper cap discoloring?

    Post by cci1492 on Fri Mar 31, 2017 10:33 am

    Thank you Peter for the info!
    I was planning on using JB weld, which is good for some crazy temp (like 400F). Used it several times in places that i was sure were going to fail....some many years ago...still waiting!!
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    Peter W.

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    Re: Weber copper cap discoloring?

    Post by Peter W. on Fri Mar 31, 2017 10:42 am

    cci1492 wrote:Thank you Peter for the info!
    I was planning on using JB weld, which is good for some crazy temp (like 400F). Used it several times in places that i was sure were going to fail....some many years ago...still waiting!!

    JB Weld is wonderful stuff. Truly once-and-done. And the "runny" stage is really good for flowing it into odd places - such as propeller shafts on RC submarines.

    Now, once-and-done = no-future-repairs-without-heroic-efforts, also.
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    cci1492

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    Re: Weber copper cap discoloring?

    Post by cci1492 on Fri Mar 31, 2017 10:56 am

    Good point!
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    deepee99

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    Re: Weber copper cap discoloring?

    Post by deepee99 on Fri Mar 31, 2017 11:07 am

    Peter W., do they have underwater RC submarine races? Laughing
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    Peter W.

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    Re: Weber copper cap discoloring?

    Post by Peter W. on Fri Mar 31, 2017 11:16 am

    deepee99 wrote:Peter W., do they have underwater RC submarine races? Laughing

    I have attended several - but was always too distracted to follow the underwater action.





    Now, on a more direct note, once upon a time, my summer house neighbor and I had identical Krick submarines (this one: http://i32.servimg.com/u/f32/15/02/95/81/k510.jpg ).

    Which we would race in the creek running in front of our houses. Until I cheated and installed high-speed propellers and flight motors Twisted Evil

    Funny thing, we had a major flood - and both the submarines were destroyed. Since, I have acquired a new kit of the same sub and I hope to start it this season.
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    cci1492

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    Re: Weber copper cap discoloring?

    Post by cci1492 on Thu Apr 06, 2017 6:57 pm

    6 holes, 3 in front 3 on the rear of the Weber resulted in it running 70-75° cooler. I'm happy with that. I ordered a pair of Genalex U77s to see how the M125s run with 200ma less....should be wonderful. lol!
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    deepee99

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    Re: Weber copper cap discoloring?

    Post by deepee99 on Thu Apr 06, 2017 7:10 pm

    cci1492 wrote:6 holes, 3 in front 3 on the rear of the Weber resulted in it running 70-75° cooler. I'm happy with that. I ordered a pair of Genalex U77s to see how the M125s run with 200ma less....should be wonderful. lol!

    I wonder why Weber didn't do that mod themselves, unless the lawyers Evil or Very Mad told them not to. Another explanation is that maybe if the copper caps ran forever Weber wouldn't have any market for replacements.
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    cci1492

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    Re: Weber copper cap discoloring?

    Post by cci1492 on Thu Apr 06, 2017 7:18 pm

    deepee99 wrote: I wonder why Weber didn't do that mod themselves, unless the lawyers Evil or Very Mad  told them not to. Another explanation is that maybe if the copper caps ran forever Weber wouldn't have any market for replacements.

    The little kid with the nail Darwin award I'm thinking.
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    skriefal

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    Re: Weber copper cap discoloring?

    Post by skriefal on Thu Apr 06, 2017 7:30 pm

    Or simply the fact that it would add time (and cost) to the production of each "tube."
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    Peter W.

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    Re: Weber copper cap discoloring?

    Post by Peter W. on Fri Apr 07, 2017 7:01 am

    skriefal wrote:Or simply the fact that it would add time (and cost) to the production of each "tube."

    They would purchase the material already punched.

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