Don´t forget with a closed chassis that inside for every 10°C temp rise over ambient temp, electroytic cap life halves, even though over the decades vast material improvements have been made. I still apply the old rule to mount where possible such caps in the lowest part of a ventilated chassis where it is cooler. The top chassis plate with multiple tube mounts can get astonishingly hot with power tube anodes on the verge of glowing in class A. If caps have to mounted on top, a heat reflecting plate fitted. Constructors cosmetics.
In the accompanying pic of this high power amp relevant ; take note of the electrolytic cap positions away from potential heat sources relevant to any such design. The perforated aluminum top chassis common to my designs implies evenings patience with a pillar drill. The under cover (not shown) also similar.
Bench baron
In the accompanying pic of this high power amp relevant ; take note of the electrolytic cap positions away from potential heat sources relevant to any such design. The perforated aluminum top chassis common to my designs implies evenings patience with a pillar drill. The under cover (not shown) also similar.
Bench baron
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I'd say the topic of fluid dynamics is not remotely obvious.
Two examples:-
1/ Clouds are up in the sky. Obviously air saturated with water vapour is less dense than the air underneath, but high clouds can also contain suspended ice crystals;,
2/ Glacial melt water from Antarctica travels 1000s of miles along the ocean bottom before finally mixing with salt water in the tropics because the flow is stratified by temperature and salinity.
It's wrong to think all fluids instantly and completely easily mix all of the time. People fit chimneys to tubes. Don't ask me whether it "helps" - I don't know!
I'm not remotely bright enough to tell you what the new convection pattern will be when you add holes, but there will be some incremental air flow by virtue of the chassis being ventilated. I'd hazard a guess and say that putting them under and around the tubes benefits the chassis components by assisting in the drawing of air out of the chassis, rather than thinking about the minor incremental benefit of air flow around the tubes.
kind regards
Marek
Hi Marek,
We are dealing with ambient air, and ambient air that has been heated from the same air mass. No need to get fancy as it doesn't vary enough to matter, only temperature.
We don't need to understand the specifics. In fact, all that might be important is a hand held anemometer. Read with holes and holes blocked, there is your answer.
We could use theory and model it, subject to assumptions. But just simply measuring it gives you an error-free answer.
We are dealing with ambient air, and ambient air that has been heated from the same air mass. No need to get fancy as it doesn't vary enough to matter, only temperature.
We don't need to understand the specifics. In fact, all that might be important is a hand held anemometer. Read with holes and holes blocked, there is your answer.
We could use theory and model it, subject to assumptions. But just simply measuring it gives you an error-free answer.
There's a text out there somewhere that talks about gas migration through heated glass of various types. In general I'd think the less hot above ambient the glass gets, the better.
What I've done with top mounted tubes is mount the socket on its own small board and hang it from the top plate with standoffs or if they're microphonic tubes, with silicone mounts that come with some case fans.
By dialing in the best distance below the top plate relative to the size of the top plate's through-hole you can net a sort of venturi effect.
I've done this a number of times, the hole size determined beforehand (of course) and then once built, running the amp perched between a couple of blocks at either end til warmed up, smoke fed in underneath , changing the length of standoffs for best effect. Worked for me. Like Anatech says try and measure. It's straightforward and doesn't take long.
In reference to Merlin's comment , with incense there's not really enough smoke to indicate anything coming out around the tube. It's too dissipated by then . What you do see is how well the smoke is drawn away from the stick , through the chassis enclosed space to the hole's proximity underneath. It's not very dramatic, though done without a bottom plate you also get a good idea where to put the bottom vents.
That was a while ago though. Now I mount everything on reusable 'local' plates and those by standoff to plywood panels then enclose the whole thing in an also reusable perforated box. Has that enticing "Hey, there's something glowing inside there." look. - Like in the old Eico enclosures . It allows everything to run cool while it keeps "experimental" wiring out of reach. I have a couple of chassis I built like that so now when it's decided to keep listening to a new build for a while I can just pull out the old board and drop in the new.
Computer cases are also great for tube amps. Especially these days being relatively cheap , solidly built of steel and with a tempered glass panel so the tube is your on light.
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Just a vintage glass holding a dry Swifter pad. Best record duster I've found and I've tried a lot!
If the tube is in free air, not in a cabinet or enclosure the heat will cause convection and take care of moving the hot air away. Those little holes in the chassis are for getting the heat out of the inside but only work if they are large enough and there are equal sized holes on the bottom of the chassis to let cooler air in. I find holes smaller than 3mm are worthless due to restriction of flow. Quantity of tiny holes does not help, it’s the restriction that matters. Don’t worry about the tube as long as you’re not pushing it to the limit causing too much dissipation.
Seems that there is nothing new here. You post a specific question, it is too quickly read by posters, and all kinds of ideas not pertaining to the question arise. Your question was simple and right at the start of the post. As far as these holes, I am thinking that there is a reasonable purpose for them around the perimeter of the tube. Especially when using a power tube that produces a good amount of heat.
OK, but those are for the internals. My question was meant if bneficial for the power tubes. See https://www.diyaudio.com/community/...-a-tube-really-make-sense.416332/post-7763301
That above a certain temperature internal parts will suffer is clear and not argued.
That's not so. The original poster asked a question based on an assumption and pretty much nobody agreed with the given assumption. Nobody offered up any measurements, so the sense in having cooling holes was answered via discussion.
The big irony is that you seem to have read post #43 too hastily and not focused on the last paragraph.
Air is going to be drawn along the top of the base of the chassis and then rise around the tube, extracting heat. Think of it as a toroidal convection cell. Locally to the tube, there is a chimney, in effect - it's a stratified flow. We now add in some escaping chassis airflow at the base of the tube via some holes. It's going to be beneficial for the chassis components to have their air join that accelerated airflow, but that is incidental to the topic. The reply to the question is that there is more air coming past the tube and there is more cooling capacity in the system, albeit this added air is already partially preheated, but it is still cooler than the surface of the 300b power tube. The air exiting the chassis at the base of the base of the 300b can still pick up some more heat as it flows past the tube and that's the answer.
If this seems hard to get, light a fire in the grate when you get home. Open the grate at the bottom and marvel how the flames burn higher and ask why that might be. It's the same "problem", expressed backwards.
Finally, the same argument is being made below here. The additional fan always adds to cooling and there's some tangible data to support it.
https://forums.jag-lovers.com/t/what-after-market-fans-do-you-recommend-for-a-series-2/408883/25
This is why other examples of the same fluid dynamics behaviour pertain to the original question - they are all governed by the same laws of physics.
kind regards
Marek
My scepticism is only that a row of holes around the tube will not cool it significantly. Since I was not certain, I asked. Significantly would be an argument for them in light of my question if beneficial for the power tubes. If the flow was so minimal that the tubes are 5C lower with them, I don't think I would bother.
Most of the discussion drifted to "do holes in the case lower the internal temperature", which is pretty obvious and was not (meant by) my question.
Don't forget that a not insignificant flow of internal tube heat is via conduction through the terminals/base, rather than just assuming it is all radiative and then assisted by convection for heat transferred to the glass. RCA 1962 identified about 10% of a 6L6 heat flow was conducted.
It depends what is exactly significantly but anything more optimal that lowers glass temp with 5 degrees is a free gift. The side effect of also getting rid of heat in the chassis only adds up to that.
Chances are that the holes make the airflow more even to the whole tube surface avoiding hotspots compared to if there weren’t any holes as there may be large obtacles like transformers blocking air flow around. If that has influence on tube lifetime is interesting to learn.
You ridiculed the class D suggestion but this heat and the hole item (and the cleaning/dusting off) are purely a result of choice. If you like to fly a direct consequence is air pollution. The one comes with the other even if undesired. Fact is that NOS tubes won’t be any cheaper or more available so having their lifetime extended by all means seems logical.
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This is a DIY forum. I only pointed out that you give this nonsense suggestion all the time. Of course, if I would only consider efficiency and heat, I would not build tube amps, let alone class A.