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  #1  
Old 07-13-2007, 08:57 PM
frotz frotz is offline
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Default Heat and noice concerns

Two things have me concerned about the design of the new 680 about

1) The power supply is mounted such that it sits directly above and very close to some chips. Is this where it was mounted in the original? It seems to me that this would cause some heat and noise problems for those chips. Perhaps the left side of the rear would be a better place for it?

2) Is there a way to have Optima take the already-made lids and punch them?

I think I already asked Grant about the second one privately.
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  #2  
Old 07-14-2007, 12:17 AM
Grant Stockly Grant Stockly is offline
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Quote:
Originally Posted by frotz View Post
Two things have me concerned about the design of the new 680 about

1) The power supply is mounted such that it sits directly above and very close to some chips. Is this where it was mounted in the original? It seems to me that this would cause some heat and noise problems for those chips. Perhaps the left side of the rear would be a better place for it?
This is where the original power supplies were mounted. I designed the power supply mounting configuration to closely match the original so that expansion cards don't hit them. The vintage and modern supplies are actually almost identical in terms of total space occupied!

Here is Tom's vintage Altair 680:


Here is Jack's 680. His are mounted on the back. This is the first time I've ever seen one like this!



I could not locate original transformers. They appear to be a custom wound transformer. Every other transformer in this frame size is 30VA, so I assume these are 30VA too. The vintage model only came with one power supply. Even in a stock configuration a lot of people found it to be insufficient. The identical transformers were then wired in parallel.

Quote:
Originally Posted by frotz View Post
2) Is there a way to have Optima take the already-made lids and punch them?

I can ask, but I am 99.999999999999999999% sure they are going to say no and have me order a new lid. I'm not sure if I could order just ONE lid, or if I would have to order multiple lids. Its possible that as early as fall I would order another batch of 680 cases. If I do then I could easily fit a lid in then. The lid would most likely be $50 or so.


Grant
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  #3  
Old 07-14-2007, 12:28 AM
Grant Stockly Grant Stockly is offline
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You could buy your own external power supply and I could chop $60 off the price of the kit. You'd need 10-11v at ~30w (I supply a PS with 60W capacity) and 16/-16v (17-18 would work too) at around 20W (I supply 40W). If you were to bypass the on board linear regulators then you could supply the exact voltages.

Those capacities assume a fully decked out vintage model. I have not measured the actual current draw of the computer. But the cost of the supplies doesn't change, so I don't try to skimp.

And here is the kit for comparison:
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  #4  
Old 07-14-2007, 06:23 AM
sje sje is offline
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Default Thermal management in the Altair 680

If I recall correctly, MITS offered the Altair 680 with an optional five inch box fan to be mounted on the back plate. For such an exhaust fan to work properly, there was a need for side vents in the case.

A big difference between then and now is the substitution of smaller and more efficient power supplies. The old style linear supplies used a lot of energy taking 60 Hz 120 VAC and beating it into submission (as we used to say) and all that energy wound up as heat inside the case. So the vents were useful with dumping that heat, and a fan was a good idea if there were any expansion cards in the machine.

If there aren't going to be any expansion cards in a replica 680, then I wouldn't be concerned about the lack of vents or a fan. However, please note that unlke the 8800, the 680 had its expansion cards mounted horizontally. And that tends to traps heat due to lack of convection. Would that be a problem? Maybe not, but consider this: would MITS have paid extra for any feature (like vents) if the feature wasn't truly needed?
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Old 07-14-2007, 02:39 PM
marty marty is offline
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Talking 680 Power supplies

Hi;
I saw in an old Mits Computer News, that enough power was sometimes a problem and they showed mounting a transformer on the outside, like one of you pictures shows. I didn't read the article, so I don't know the particulars. Thanks Marty
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  #6  
Old 07-14-2007, 11:12 PM
frotz frotz is offline
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I have a vintage IMSAI 8080 that has transformers mounted on the outside like that.
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