bluefoxicy Posted April 17, 2008 Share Posted April 17, 2008 a 40mm fan won't draw much current right? I'm thinking of running a 3.3V 40mm off the filament coils and exhausting air from the back of the chassis. The first power resistor emits tons of heat, so it gets hot in there; it may be good to have air exhaust out the chassis, with the negative pressure causing air to flow past the 12AX7 and EL34 from in the cabinet (most available airspace is that EL34's hole) Link to comment Share on other sites More sharing options...
TWANG Posted April 17, 2008 Share Posted April 17, 2008 wont that add noise, too? Link to comment Share on other sites More sharing options...
bluefoxicy Posted April 17, 2008 Author Share Posted April 17, 2008 Not if I use a filter cap and a coupling resistor going to the fan (it needs bridge rectification to run). A ball bearing fan will add minimal mechanical noise too. Link to comment Share on other sites More sharing options...
TWANG Posted April 17, 2008 Share Posted April 17, 2008 If you want to tell me how to do that, I might try it myself! Link to comment Share on other sites More sharing options...
bluefoxicy Posted April 17, 2008 Author Share Posted April 17, 2008 I have to find a fan that eats less than 0.9A first. Probably won't be hard (CPU fan), considering I need a RESISTOR to drop the voltage from 6.3V to likely 3.3V (maybe 5V though!) and the only thing I know is E - I/R = 0. Seriously though, a fan is just a motor. It has blades on it but that's plastic crap. If you run a current-drawing load in parallel with an existing circuit it drops resistance, keeps the voltage the same, and raises overall current draw. Exactly what's the BEST way to do this, I can't tell you; a LOT of ways will WORK but some will probably introduce hum. As for mounting the fan, that I can tell you. Cut a hole in the back of the chassis on the side further away from the tubes, just smaller than the frame of the fan but NOT smaller than the blades. Outline it with rubber (cut a square pad to fit, or use a bead of silicon caulk). Mount the fan there, screw it down to create a seal. Run the fan such that it EXHAUSTS air, creating negative pressure in the chassis and sucking air in through other holes, mainly around the power tube (biggest overall open area, compared to volume pot and used input jack; the output jacks may contend with this, unless they're closed plastic housed). The reason for this mounting of the fan is simple. A fan works most efficiently in a tube slightly wider than the blades, which you just effectively sealed to the hole in the back of the chassis. More air flows in around the power tube (which is trying to cool off anyway; only the part in the center should be hot); but, more to my interest, cool air (a fast enough flow of cool air past a hot component only gets a little warm!) enters the chassis as far away as possible from the exhaust port! It gets dragged in from everywhere, runs over the cap and resistor, and vents. A quiet ball bearing fan and a loud guitar will eliminate concerns from mechanical hum Remember though, I'm using an EL34 with full 25W bias on a bigger PT. R10 burned up (smoke came out of my amp, but the resistor itself only scorched a bit) and a 5W flameproof still had a slight smell and was very VERY hot. 10W works, 25W R10 will still burn the HELL out of your hand, it doesn't matter it's still dissipating X watts of heat no matter how much it can handle (it's a resistor, it's dissipating some of that power as heat...) so unless it gets HUGE it's going to be hot. It's HOT inside my case, the caps get hot too, I want them cooled and sucking air past that resistor will make a huge difference for me. Link to comment Share on other sites More sharing options...
m-theory Posted April 18, 2008 Share Posted April 18, 2008 Your fan housing doesn't need to be sealed, and it doesn't have to exhaust. All you really need is a bit of air movement. Even removing the back cover will give you enough air movement to keep things cool. You'd be surprised how little air it really takes to keep things cool. Here's an article on installing a brushless fan on a vintage Fender. An amp tech friend of mine isn't real hip to using PT juice for a fan, but not for any specific reason other than that he feels the PT has more important things to do than feed power to a fan. Personally, I can't see where drawing a tiny amount of current to run a small fan would cause current shortages elsewhere or put any real strain on a real PT, however, though I went out and bought a small clip-in instead, on his advice. My '66 Bassman is fully plexi-modded, and I run it at full throttle, with this little fan clipped onto the back. For some reason that I cannot really explain, I've never had a hum issue with this fan, even though it's a cheapie deluxe and is not brushless. By all rights, it SHOULD be introducing hum. Brushless would obviously be the way to go to avoid hum, but it's clearly not always a necessity. Link to comment Share on other sites More sharing options...
TWANG Posted April 18, 2008 Share Posted April 18, 2008 remember those little fan blades in a glass ball. the sun would hit them and they'd spin. I was thinking.. if you could get a good enough bearing for those, the heat the amp generates would spin them.. but would it spin enough to get air moving? sure would be cheap and quiet! Link to comment Share on other sites More sharing options...
bluefoxicy Posted April 18, 2008 Author Share Posted April 18, 2008 Your fan housing doesn't need to be sealed' date=' and it doesn't have to exhaust. All you really need is a bit of air movement. Even removing the back cover will give you enough air movement to keep things cool. You'd be surprised how little air it really takes to keep things cool.[/quote'] In other news, you don't need a properly constructed bucket to move water; a few small cracks and holes still will let you get a decent amount of water from point A to point B. You might as well go with the optimum design if it's trivial. You can skip sealing it, you can make it intake but back pressure comes into effect slightly faster, etc. It's not "critical" but it's the "best" way. Link to comment Share on other sites More sharing options...
bluefoxicy Posted April 18, 2008 Author Share Posted April 18, 2008 remember those little fan blades in a glass ball. the sun would hit them and they'd spin. I was thinking.. if you could get a good enough bearing for those' date=' the heat the amp generates would spin them.. but would it spin enough to get air moving? sure would be cheap and quiet! [/quote'] Those work because one side reflects heat and the other is black on each blade. The light hits the shiny side and bounces off; but when it hits the black side, it gets absorbed, increasing the energy in that side of the blade. Raise the energy enough and it becomes a driving force. If you have a 25W biased power tube like me and your R10 is freaking hot, you could run long legs out to a seated sterling engine and thermal paste it together. A gamma sterling engine will run on the difference between your palm and ambient air temperature. Hell, you can build a beta sterling engine out of a couple coke cans and use a tea candle to drive it. Link to comment Share on other sites More sharing options...
m-theory Posted April 18, 2008 Share Posted April 18, 2008 In other news, you don't need a properly constructed bucket to move water; a few small cracks and holes still will let you get a decent amount of water from point A to point B. In other words, in your vision, the only way for a human to breathe oxygen is to be locked in a room entirely void of all other gases. It's an absurd analogy that means nothing. You don't need anything sealed to make a fan blow air, and you don't need massive gusts of wind to keep an amp cool. You merely need a small bit of air flow, such as you'd get by removing the back panel of the amp. If you're amp is running so hot that you need to seal it in a hyperbolic chamber and run a megawatt fan directly across it, you've got problems beyond fan installation. Link to comment Share on other sites More sharing options...
m-theory Posted April 18, 2008 Share Posted April 18, 2008 Oh man...I just read that again, and I sound like an ***. Sorry about that! Look, you can do whatever you think you have to do, but all I'm saying is that it's really not necessary to create a vacuum seal anywhere, in order for a small fan to have a huge impact on lowering amp temps. Just some air movement is really all that you need. There's really no right or wrong way, if air movement is the goal, and your method produces air movement. My Vjr runs with the back panel off, and it's fine. My Bassman gets a small clip-on fan, and it runs fine. A small CPU fan mounted inside the cabinet would work fine, with or without a sealed venting system. All methods move air, which is really all you're trying to accomplish. Link to comment Share on other sites More sharing options...
bluefoxicy Posted April 18, 2008 Author Share Posted April 18, 2008 lol, yeah I was giving the purist optimal-air-flow way (I used to talk to an aerospace engi... a rocket scientist regularly). I was going to bounce something back but decided this argument is stupid and I'm not having it nobody's actually wrong here. Interesting that you've actually tried some passive and active cooling. I'm actually considering gluing my R10 to the case with thermal paste at this point to raise surface area, since I am far too lazy to put in a fan TODAY (maybe in a week or two). http://www.newegg.com/Product/Product.aspx?Item=N82E16811999701 Hmm. 40mm, 12CFM air flow, 12V 0.79A (6.3V full wave bridge == 9V... close enough, R stays the same so this will reduce amperage which is good for my little 270DAX, which only wants to give 1.4A more out the filaments). Suck? $5 for the fan and $6 to ship! Link to comment Share on other sites More sharing options...
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