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Old 20th December 2004, 03:18 AM   #1
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Default Tube Cooling Recommendations

Help,
I recently told a fellow audiophile that i was going to fit a cooling fan to my latest tube amp project. His response was a flat "fans do not belong in HiFi Amplifiers".

I believe there MUST be suitable engineering solution to adding a fan to a tube amp which can only enhance its reliability.

Yes there are acoustic noise level issues to solve but it should be practical.

There are a couple of "rules of thumb" and application hints like:
1) Always use the fan to blow INTO the equipment so that the box acts as an acoustic baffle.
2) Use a DC fan and run it at half voltage
etc.

I believe that it is more important to choose the right sort of fan in the first place - the problem is that I don't know what that type might be.

Any ideas/suggestions?

Cheers,
Ian
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Old 20th December 2004, 03:49 AM   #2
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Hi,

Quote:
Any ideas/suggestions?
Well...
If you must cool tubes why not take a look at what Bill Perkins of Pearl-Hifi came up with?

I think the major concern with the heat generated by the tubes and power resistors is a long-term reliability issue, caps drying out due to excessive heat etc.
Most of this can be circumvented by careful layout and providing sufficient airflow IME, still:


TUBE COOLERS

Cheers,
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Old 20th December 2004, 04:32 AM   #3
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I'm with fdegrove, heat problems in tube circuits are really layout/ventillation problems in disguise. Make sure that the tubes are properly spaced and allow for air flow around the base of power tubes, either by drilling holes in the chassis or having an oversized hole around the socket with the socket mounted on the circuit board or standoffs. Make sure that there's a place for cool air to enter the chassis. I can't count the number of times that I've seen equipment with air holes in the top (where the builder or customer could look in and observe the glowing tubes), but none on the sides or bottom where air could enter. I like looking at tubes as much as the next guy, but I also like knowing that there's sufficient ventillation.
Incidentally, a good rule of thumb is to space tubes at least two tube-diameters apart, on center. If you have a 1.5" tube, set them 3" apart or more. Some spec sheets have recommended minimum spacings. If so, adhere to them.
With attention to details, convection is sufficient. It's completely silent and doesn't introduce magnetic fields into your circuitry. And it costs less, too.

Grey
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Old 20th December 2004, 05:19 AM   #4
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Default The problem children

I've done as above as much as possible - the tubes are a liitle close together for my complete satisfaction BUT this was dictated by the PCB I used (Menno van der Venne BBB70100).

40mm holes around the EL34s which plug thru into a PCB.

No bases on the boxes as yet hence them sitting on the timber to allow air flow from underneath.

EL34s in triode mode giving about 40 watts Output Power.

Thanks,
Ian
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Old 20th December 2004, 06:05 AM   #5
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I have little area to play with stereo equipment in my house, so building compact is a must. This means undersized cabinets and fan cooling. Just use a quiet computer fan. Local thrift stores sell them (new and pulls) for 50 cents to $2. I snagged the whole box and reserve the quiets for HiFi
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Old 20th December 2004, 06:42 AM   #6
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Bah, I'm sitting next to three fans right now. I can't hear them worth a damn, the music is 10-20dB louder than them

At worst, you can add acoustic damping materials, ducting and whatnot to keep the sound both contained and damped.

Tim
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Old 20th December 2004, 08:21 AM   #7
SHiFTY is offline SHiFTY  New Zealand
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Output tubes: designed to run hot... But leave a good spacing between them, a ventilation gap at the base (or drilled holes) and if possible mount them down into the chassis a little. Also don't run them past their ratings, even in class A.

Power resistors: Mount as far away from capacitors and other circuitry as practical. If possible have some mesh above them.

One thing that is useful is chassis ventialtion: by having some places for hot air to escape, cold air can be drawn in through the bottom of the amp and keep it cool.

But:

If you do use a fan, I would mount it actually in the base of the amp, blowing upwards (ie sucking cold air from underneath the amp.) Use a 12V "stealth" fan running at 6VDC for maximum quietness. You can buy quiet PC fans (for example the Vantec stealth) and even in low profile.
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Old 20th December 2004, 08:31 AM   #8
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keep the amps in the fridge.
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Old 20th December 2004, 09:30 AM   #9
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I generally build amps vertically, with the PS at the bottom and the analog sections at or near the top. I leave lots of space between tubes, holes/spaces around sockets etc, room for air to enter, and I think about the thermal design as I lay it out. No heat issues here. However, I have used fans to cool before when I've used transmitter tubes, run at low speed (damn near silent from listening position) from the bottom pushing the air up past the tubes. In my house it can easily get into the high 30's in summer.
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Old 20th December 2004, 10:40 AM   #10
EC8010 is offline EC8010  United Kingdom
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Would you gentlemen please not remind me of high temperatures. My circulating pump failed last night night and I'm waiting for the system to drain down sufficiently so that I can replace it (the valves either side didn't work). As I shiver here, I can assure you that my amplifiers currently have no cooling problems whatsoever.
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