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Old 31st January 2004, 02:06 AM   #1
7V is offline 7V  United Kingdom
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Default I could lose some heat - suggestions?

I've got a valve (tube) active filter for my bass speakers - uses miniature tubes, marvellous. The cabinet is very compact - it's aluminium and a bit of a tight squeeze.

The unit works beautifully but the top of the cabinet gets quite hot which worries me somewhat. The valves themselves are mounted on the pcb, insulated from the cabinet. I'd like to improve the heat situation a little.

Could I spray the top matt black to increase the heat radiation or would I be better off drilling holes in it or adding a heatsink to the top of the case? I probably don't need to take away a great deal of heat.

Thanks in advance for your help.
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Old 31st January 2004, 02:20 AM   #2
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Drilling holes and adding some sort of forced ventalation (as in a fan) would be the way to go. If you are using something like 12AX7 size tubes and assuming you have less than 6 tubes, a computer CPU fan might be all you need. They are small, plentiful, can be quiet.

Or a regular DC equipment (muffin) style fan run at a lower voltage. Example: a 24 Volts DC fan running at 16 Volts DC, to make it more quiet.

Fans may be a pain in the neck, but smoke and fire are worse.

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Old 31st January 2004, 11:20 AM   #3
7V is offline 7V  United Kingdom
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Quote:
Originally posted by Aud_Mot
Drilling holes and adding some sort of forced ventalation (as in a fan) would be the way to go. If you are using something like 12AX7 size tubes and assuming you have less than 6 tubes, a computer CPU fan might be all you need. They are small, plentiful, can be quiet.
Thanks for your suggestion, Aud_Mot.

There are only 3 miniature tubes and they are much smaller than 12AX7s. I don't have enough room in the cabinet for a fan and would need a new cabinet.

I don't think I need to cool the unit that much, just take a little more of the heat out. I believe that either of the following approaches would be sufficient:

1. Spraying the top matt black
2. Drilling holes in the top (and letting convection do the work)
3. Adding some type of finned heat sink to the top of the cabinet.

I wondered which of these would give the best results.
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Old 31st January 2004, 04:41 PM   #4
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7V,

First - let me say that my answers are more intuative than based on any engineering knowledge or special training.

I do know black "gives off" heat better than other colors. This was explained by some one on this forum, "The same principle/properties that allow black to absorb heat, allows it to give off heat." You are right that matte black is better than shiny black.

Drilling holes on the top would be good. Can you drill holes on any of the sides? This would allow a 2nd path of fresh air to get into the box, instead of cool air and hot air trying to enter and escape through the same holes.

The heat sink on top could help. If you leave your cross over on all the time, (most audiophiles like to keep their electronics warmed up) you might only be delaying the overheating situation. Air is a a poor conductor of heat. You will have to heat up the air around your tubes first, then the hot air will heat up the box and heat sink, then the heat gets radiated into the room.

Sorry - I keep coming back to a fan. Are you familiar with the small ones available for CPUs on Personal computers? They can be very small, 1 inch square. Can you put a fan on the outside of the box? It might be ugly, but it would work.

If fan noise is a problem and you leave your cross over on, you can add a switch and turn off the fan during listening sessions. Assuming it takes a while to build up the heat to a dangerous level, it might be a nice solution.

Please let the forum know what worked for you.

Aud_Mot
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Old 31st January 2004, 04:57 PM   #5
7V is offline 7V  United Kingdom
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Quote:
Originally posted by Aud_Mot
Please let the forum know what worked for you.
Thanks Aud_Mot. I think I'll start by spraying matt black. Then, if necessary, I'll drill some holes in the tops and, as you suggested, the sides.

I'll report back.
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Old 31st January 2004, 05:29 PM   #6
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7V, take a look at what people did back 40-50 years ago for tube equipment meant for home use: perfed tops and either holes or slots on the bottom, with the bottom raised up on feet. That gives the air a straight convection path. For what you're doing, I seriously doubt you'll need a fan.
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Old 31st January 2004, 07:02 PM   #7
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Quote:
Originally posted by SY
7V, take a look at what people did back 40-50 years ago for tube equipment meant for home use
Yes, it all comes flooding back to me. The secret's in the tiny perforations.
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Old 31st January 2004, 08:06 PM   #8
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My preamp is stored in my desk drawer, so it's insulated on all sides with wood - granted 90% of the time the drawer is cracked so I can get at the knobs, but even closed for several hours it gets only comfortably warm. (Although during summer that'll be about 25F warmer than comfortable, possibly a cause for concern in the capacitors and PT.) The 12AT7 and 'AU are running a little warm, making for maybe 10W total consumption in the thing.

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Old 1st February 2004, 05:47 AM   #9
SHiFTY is offline SHiFTY  New Zealand
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How hot exactly is the box getting? Tubes do run kind of hot you know!

You might want to try replacing the baseplate with mesh, and drilling some holes to improve airflow. Don't mess up your creation without good reason though.

What tubes are you using?
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Old 1st February 2004, 10:31 AM   #10
7V is offline 7V  United Kingdom
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Quote:
Originally posted by ShiFtY
How hot exactly is the box getting? Tubes do run kind of hot you know!

You might want to try replacing the baseplate with mesh, and drilling some holes to improve airflow. Don't mess up your creation without good reason though.

What tubes are you using?
The tubes are dual miniature triodes (tiny things). I don't know the exact type because the unit was designed for me by Chris Found (who once did the Beard amps). It's a bit tight to get it in and out of the aluminium cabinet which is a sleeve type - no separate top or bottom. The circuit board slides in through the ends. I will find out the exact tube type later but you know me - I'm just a speaker designer.

The hottest part in operation is the top of the cabinet and I can still put my hand on this. The reason I'm worried is that a tube heater regulator blew. However, this has been given a better heatsink and the unit has been ok since. Still, a little extra cooling won't hurt.

My current thinking is to start by spraying the top matt black. This may be sufficient. As you say, tubes do run hot.

Thanks.
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