Pretend for a moment I never studied thermal engineering. Will black paint help? - Page 1
Forum section: electronics / projects

author: cvanc
author_rank: Frequent Contributor
timestamp: September 23, 2023, 12:17:54 pm
content: So these are weird audio amplifiers and I am trying to get the tubes to run cooler without adding a fan.The tubes operate horizontally & are close to and parallel with the unpainted aluminum floor. Infrared images show a strong heat reflection on the sheet metal. I assume this reflection bounces heat right back up to the tubes.Will the tubes run cooler if I paint the floor of the amps black? Thanks...

author: moffy
author_rank: Super Contributor
timestamp: September 23, 2023, 12:37:03 pm
content: You could try and see. My guess is that you need a fan.

author: strawberry
author_rank: Super Contributor
timestamp: September 23, 2023, 01:10:32 pm
content: Aluminium folded sheet heatsink or water cooling with silicone tubes coiled around vacuum tubes

author: Tomorokoshi
author_rank: Super Contributor
timestamp: September 23, 2023, 01:37:52 pm
content: Quote from: cvanc on September 23, 2023, 12:17:54 pm1. What is above the tubes? A solid panel? How high?2. Can you post the IR picture?3. Most tube chassis have slots or holes punched in them for air flow. Is that an option?4. Some heat will reflect back up, some will conduct through the metal. It isn't a mirror finish, so it will be diffused away by some amount. Painting might insulate about as much as it helps. Usually aluminum heatsinks would be black anodized for that effect.5. Can you get temperature readings at the aluminum immediately below the tube?6. Can the assembly be raised by an inch or two?

author: coromonadalix
author_rank: Super Contributor
timestamp: September 23, 2023, 01:56:56 pm
content: 1st i would never lay tubes flat, its worselet them stand up as they should ... like this they dont radiate their heat evenly or efficientlythis design loose efficiency and practicalitysorry its a messDo a proper enclosure first, redo your design to put them straight

author: ch_scr
author_rank: Frequent Contributor
timestamp: September 23, 2023, 01:59:47 pm
content: If you want to dissipate the heat through the metal panel (the panel will become hotter, but the tubes might run cooler) - you would have to paint it on both sides. The inside for the heat to be taken up, the outside for the heat to be effectively radiated. If it isn't an option to paint e.g. the outside black,anycolour will be at least 90% as good, and way better than no paint.

author: Bud
author_rank: Super Contributor
timestamp: September 23, 2023, 02:14:07 pm
content: What is wrong with ventilation holes? It would be weird for a tube gear to not have ventilation holes. Bets are holes will be more effective than painting. Also check the tubes datsheet for operating temperature specs.

author: TimFox
author_rank: Super Contributor
timestamp: September 23, 2023, 05:10:37 pm
content: I'm a little worried about those plate-cap wires passing by the hot envelopes of the power tubes without support: what is their insulation's temperature rating?

author: IanB
author_rank: Super Contributor
timestamp: September 23, 2023, 05:41:04 pm
content: You need air flow. Either by natural convection or forced convection (fan). For natural convection, the normal practice is to have lots of vent holes, and arrange a clear path for cool air to flow in at the bottom and warm air to flow out at the top.All tube equipment I have seen has had lots (and lots and lots) of vent holes in the case.Also, I don't recall seeing tubes mounted horizontally. I have always seen them mounted upright.Painting the inside of the case black may help if you paint the outside of the case black too. This way the case metal will do a better job of absorbing heat and radiating it to the surroundings. But in general, the cooling solution is air flow, air flow, air flow.

author: TimFox
author_rank: Super Contributor
timestamp: September 23, 2023, 05:48:27 pm
content: Tubes are often mounted horizontally (especially in 3.5" high rack-mount chassis such as my Kepco power supplies).Check the datasheet for the individual tube: they often require a specific orientation of the socket with respect to vertical to avoid problems with sag of internal bits.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 24, 2023, 07:21:11 am
content: Quote from: cvanc on September 23, 2023, 12:17:54 pmWhy not add a fan ? There is plenty of room, and to does not need to be moving shiploads of air.Quote from: cvanc on September 23, 2023, 12:17:54 pmfind some true black high temperature paint, and try one to compare ?I love the burnt wood.The valves are very close together and with poor possible air flow, so the design is already seriously compromised.Adding a fan may save you a complete redesign. (and a steady supply of replacement valves)

author: cvanc
author_rank: Frequent Contributor
timestamp: September 24, 2023, 12:25:28 pm
content: Someone finally noticed my lumber mod. Yeah that didn't last long ":^)I know these look like homemade CB linears I made in my garage but they're a commercial audio product from the 70's. On the other hand perhaps the vendor, long defunct, built them in *his* garage!I long ago deleted the fans and covers to quiet my room. I've run for years like this and it works fine but the appetite for new tubes is higher than desired (isn't it always?).Poking around with my FLIR I find the tubes operate at 450°. The datasheet - 36KD6 for those interested - says 450° is the rated maximum. It seems prudent to reduce this. However no noise is allowed; I want to use passive means only. I'm wondering about a simple chimney as well.Thank you all for your insights.

author: 741
author_rank: Frequent Contributor
timestamp: September 24, 2023, 01:24:56 pm
content: Is there a way to paint patches of black on the shiny chassis in a pattern that promotes air movement?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 24, 2023, 01:28:54 pm
content: Quote from: cvanc on September 24, 2023, 12:25:28 pmTry some Noctua fans?