Re: [Drakelist] AC4 heat Fan Summary
On Dec 16, 2010, at 8:02 PM, Jim Shorney wrote: On Thu, 16 Dec 2010 12:32:48 -0500, mike bryce wrote: should it blow in or suck out? This would seem to be a question of spot cooling vs. system cooling. I'll chime in with my $0.02 here... The suck it out versus blow it in debate (aka negative pressure versus positive pressure ventilation) has been raging for years in the fire service. When I went through firefighter training 25 years ago, the current wisdom was leaning in favor of positive pressure, but this has shifted a couple of times. These days both are in favor, but use varies depending on the space you need to ventilate. Generally, positive pressure is going to create a column of pressurized air with most of the effort going in one direction and is best for a limited space with few entrances and exits, whereas negative pressure will draw air from any place air can come from, and what you get is better although lower pressure evacuation of many spaces. I prefer negative pressure for my Twins and TR-4 as it can help draw warmer air from many places in the rig, not just the finals, although the finals are where most of the benefit will be found. It also limits the incoming dust being concentrated heavily in one location, which aids in periodic cleaning. Tom -- Tom Swisher, WA8PYR A wise and frugal government, which shall leave men free to regulate their own pursuits of industry and improvement, and shall not take from the mouth of labor the bread it has earned - this is the sum of good government. - Thomas Jefferson ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
Hi Damien: I perhaps got a little too annoyed at reading some of the cr*p that gets passed off on line as worthwhile technical information. Anyway...too issues going on really. 1. Do the AC4 or any other Drake or similar units need fans? 2. How to implement fans..especially blowing in or out. For 1. Do they need fans. I would say, technically no..most have lasted over 40 years without them The fact is however, that the service life of electronics is extended greatly if they are kept cooler. In the 60s, adding a fan to a rig was an expensive proposition..thats why many manufacturers made them optional. I am sure Drake never had an engineering discussion about lets make sure these rigs are still working fine in 2010 !! They did however have discussions about maximizing performance at chosen price points. Today, adding a quiet, small fan is trivial...so I opt to do it..as do many others. The only real issue with the AC4 is that holes must be drilled in the cover. I got over that once I replaced all of the original filter caps, rectifiers and bleeders with the Heathkit shop upgrade board. I use my Drake rigs; a lot. When they are on, they stay on for 12-16 hours at a time and frequently I run RTTY contests, or CW contests with them. If a collection just sits there and never runs more than a couple hours a month, I'm sure there is not much need for a fan--anywhere in the system. Even the PS7 however, has an optional location for an 80mm exhaust fan. And it is a large open enclosure compared to the AC4 and also has perforated covers. It is interesting to note that the AC3 had no cover. I suspect that Drake felt some safety pressure to cover the PS. Also...the fact that the cover on the AC4 is aluminum I suspect is not just coincidence but a thermal decision as well. This could have been perferrated steel like the rest of the line. Why not? I suspect that the solid aluminum cover is better thermally..aluminum is MUCH more conductive than steel. Its a big heat radiator. As for question 2, all of these small fans are designed to move air in only one direction. They also are designed to work with a very small negative pressure on the draw side...there ability to function drops to nearly zero if they work against a positive pressure on the exhaust side. SO...unless there is zero restriction in the path, they should always be run pulling air and not pushing it. A simple experiment can prove this. Put a 40W lightbulb in a cardboard box and put a fan on it pointing in. seal it up with a thermometer and turn on the fan and lite and watch the temp. Poke a few small holes in the box and watch wat happensnot much. Now turn the fan around so it pulls air out..air will be drawn into the holes you made..the temp will drop fast. Or just remember what happens when the bag (creating pressure on the fan) in your vacuum cleaner gets plugged. Not much air flow going in then. Confusion occurs I think because people think about things like there furnace or a linear with forced air cooling. There are blowers that ARE designed to work against positive pressure. Squirrel cage blowers for example. In this case, the blower is able to pressurize the enclosure and the warm air is expelled thru vents in the box. The fundamental design of the blower is different. In fact, small fans can't operate very well with much suction either but really die with pressure. They are designed to operate in a moving stream of air. Restrict the stream, and efficiency drops drastically. The AC4 is really a excellent setup for cooling. The slots around the cover low and high offer a fair amount of total cross section open area, and when the fan draws air out of the box, the ingoing fresh air is distributed thruout the enclosure and exhausted via the fan. No dead air and constant, low level flow. A great setup would be the fan exausting from one end and inlet holes in the opposite end. I looked at doing that but then the PS would not fit inside the MS4. Across Yaesu, ICOM, and the Drake TR7, ALL of the fans, standard and optional, draw air out of the enclosures. This maximizes the efficiency of the fan operation, reduces the chance of dead air hot spots. So..I am staying with my approach to utilize fans on all of my drake and other equipment..I'll have the R-4 fan install pix added soon to the picture album..as noted before, it keeps the r4 audio tube heat from the transformer and in the process, improved the initial vfo drift performance as well. Will the AC4 drop dead without a fan? No, surely not. Will it last longer with one? Absolutely. In the interest of closure, I will post this to Drakelist as well Damien. As always, questions or comments are welcomed. Curt KU8L Damien Mannix wrote: Been following this thread with great interest. Thanks guys. I do not understand the dynamics but am anxious to learn. Do I gather
Re: [Drakelist] AC4 heat Fan Summary
- Original Message - From: Curt Nixon cptc...@flash.net To: Damien Mannix damienman...@hotmail.com; drakelist Drakelist@zerobeat.net Sent: Thursday, December 16, 2010 8:41 AM Subject: Re: [Drakelist] AC4 heat Fan Summary Hi Damien: I perhaps got a little too annoyed at reading some of the cr*p that gets passed off on line as worthwhile technical information. Anyway...too issues going on really. 1. Do the AC4 or any other Drake or similar units need fans? 2. How to implement fans..especially blowing in or out. For 1. Do they need fans. I would say, technically no..most have lasted over 40 years without them The fact is however, that the service life of electronics is extended greatly if they are kept cooler. In the 60s, adding a fan to a rig was an expensive proposition..thats why many manufacturers made them optional. I am sure Drake never had an engineering discussion about lets make sure these rigs are still working fine in 2010 !! They did however have discussions about maximizing performance at chosen price points. Today, adding a quiet, small fan is trivial...so I opt to do it..as do many others. The only real issue with the AC4 is that holes must be drilled in the cover. I got over that once I replaced all of the original filter caps, rectifiers and bleeders with the Heathkit shop upgrade board. I use my Drake rigs; a lot. When they are on, they stay on for 12-16 hours at a time and frequently I run RTTY contests, or CW contests with them. If a collection just sits there and never runs more than a couple hours a month, I'm sure there is not much need for a fan--anywhere in the system. Even the PS7 however, has an optional location for an 80mm exhaust fan. And it is a large open enclosure compared to the AC4 and also has perforated covers. It is interesting to note that the AC3 had no cover. I suspect that Drake felt some safety pressure to cover the PS. Also...the fact that the cover on the AC4 is aluminum I suspect is not just coincidence but a thermal decision as well. This could have been perferrated steel like the rest of the line. Why not? I suspect that the solid aluminum cover is better thermally..aluminum is MUCH more conductive than steel. Its a big heat radiator. As for question 2, all of these small fans are designed to move air in only one direction. They also are designed to work with a very small negative pressure on the draw side...there ability to function drops to nearly zero if they work against a positive pressure on the exhaust side. SO...unless there is zero restriction in the path, they should always be run pulling air and not pushing it. A simple experiment can prove this. Put a 40W lightbulb in a cardboard box and put a fan on it pointing in. seal it up with a thermometer and turn on the fan and lite and watch the temp. Poke a few small holes in the box and watch wat happensnot much. Now turn the fan around so it pulls air out..air will be drawn into the holes you made..the temp will drop fast. Or just remember what happens when the bag (creating pressure on the fan) in your vacuum cleaner gets plugged. Not much air flow going in then. Confusion occurs I think because people think about things like there furnace or a linear with forced air cooling. There are blowers that ARE designed to work against positive pressure. Squirrel cage blowers for example. In this case, the blower is able to pressurize the enclosure and the warm air is expelled thru vents in the box. The fundamental design of the blower is different. In fact, small fans can't operate very well with much suction either but really die with pressure. They are designed to operate in a moving stream of air. Restrict the stream, and efficiency drops drastically. The AC4 is really a excellent setup for cooling. The slots around the cover low and high offer a fair amount of total cross section open area, and when the fan draws air out of the box, the ingoing fresh air is distributed thruout the enclosure and exhausted via the fan. No dead air and constant, low level flow. A great setup would be the fan exausting from one end and inlet holes in the opposite end. I looked at doing that but then the PS would not fit inside the MS4. Across Yaesu, ICOM, and the Drake TR7, ALL of the fans, standard and optional, draw air out of the enclosures. This maximizes the efficiency of the fan operation, reduces the chance of dead air hot spots. So..I am staying with my approach to utilize fans on all of my drake and other equipment..I'll have the R-4 fan install pix added soon to the picture album..as noted before, it keeps the r4 audio tube heat from the transformer and in the process, improved the initial vfo drift performance as well. Will the AC4 drop dead without a fan? No, surely not. Will it last longer with one? Absolutely. In the interest of closure, I will post
Re: [Drakelist] AC4 heat Fan Summary
thought I'd toss my .02 in with a question on the tr series, a fan mounted to the rear of the pa compartment, should it blow in or suck out? since we're not trying to pressurize a compartment, there's plenty of holes in the cage and top cover, and since heat rises, it would seem to me that one would mount the fan so it would blow into and onto the final tubes To me, it seems a fan sucking air out of the pa compartment would have to compete with the natural convention of heat raising so, what's the word from the thermal gods? Mike, WB8VGE SunLight Energy Systems The Heathkit Shop http://www.theheathkitshop.com/ J e e p o|||o If the facts don't fit the theory, change the facts. Albert Einstein ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
Mike, I still vote for the suck it out feature, top mounted or rear mounted. You do NOT want to blow that hot air across the finals and directly to the PTO. It already drifts enough, and the gentle cooling by pulling air out will lower the inside temperature drastically AND allow the PTO to stabilize sooner. Try it 73, ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
By the way, I am NOT a thermal god, but just an old fashioned, near 40 year user of Drake products. 73___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
- Original Message - From: mike bryce proso...@sssnet.com To: Richard Knoppow 1oldle...@ix.netcom.com Cc: captc...@flash.net; Drakelist@zerobeat.net Sent: Thursday, December 16, 2010 9:32 AM Subject: Re: [Drakelist] AC4 heat Fan Summary thought I'd toss my .02 in with a question on the tr series, a fan mounted to the rear of the pa compartment, should it blow in or suck out? since we're not trying to pressurize a compartment, there's plenty of holes in the cage and top cover, and since heat rises, it would seem to me that one would mount the fan so it would blow into and onto the final tubes To me, it seems a fan sucking air out of the pa compartment would have to compete with the natural convention of heat raising so, what's the word from the thermal gods? Mike, WB8VGE SunLight Energy Systems The Heathkit Shop http://www.theheathkitshop.com/ I noted this in my little diatribe. For the T4 the fan works best sucking the heat out from the top. Its very simple and works. Most of the heat in this TX comes from the finals and is concentrated in the final compartment. While it is in a perforated metal enclosure there is a lot of heat generated in a small area plus the addition of the external cabinet further interferes with both direct radiation of heat and convection. A small fan very significantly reduces the heat. Much of what I wrote has to do with completely enclosed spaces where the conditions are quite different from the above. Where you can control the air flow there are advantages to positive pressure but, again, one must be careful to plot out the flow of _heat_ to insure one is not getting unintended heating rather than cooling. Actually, that's the problem with using a pushing fan on something like the T4, the heat is pushed out around other components and can heat them up where the sucking fan draws cool air from around the tubes and exhausts it directly to the air. I mainly wanted to point out the differences between cooling a basically open area like the T4 final cage and a completely enclosed space like the AC-4. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
GA Mike: Sure, as far as the air movement is concerned, I don't think there is anything wrong with that thinking. But the relative amount of air movement from the natural convection is very small compared to the amount created by the fan. I think the controlling issue, in this case is the efficiency of the fan. As Richard explained, by creating a small negative pressure (suction) with the fan, air will enter the Tx from everywhere. More from the areas of least restriction..like the vent holes around the tube sockets and screen over large hole beneath the finals compartment...and move up and out thru the fan. This small but widely distributed exchange of air is the best situation for the rig as a whole. It is not necessary to blow air across these tubes to cool them..just endeaver to keep the ambient air surrounding them at some lower nominal temperature...the glass tube can conduct the internal heat away pretty well as long as the air is not totally stagnant. If appearance was no issue, I would put the fan, drawing out, right on top of the final cage. But since the cage is perforated, placing it on the back is nearly as effective and looks better :) The fan easily overcomes the normal convection path that would be straight up and the bonus is you exchange air pretty much throughout the rig. BTW..these fans are EXTREMELY sensitive to the smallest backpressure. They pressureize a compartment..that is the whole point. If they could, it wouldn't make any difference to the rig, as Richard explained. It doesn't care which direction the air goes, just that it is exchanged for cooler air. The fan DOES care tho. Even the perforated cages present a significant back pressure to one of these fans. Try it...use an incense stick and put the fan right against the cage blowing in...smoke stick on opposite side. Now try it with fan pulling air thru the perf panel. You will see the difference. When I played with the R4 fan install, I did some very interesting flow experiments using incense sticks for smoke and watched where the air was going. It is very easy to tell the difference in pressure v suction when doing this. Will they work blowing in? sure..they worked 40 years w no fan. m They just work better pulling air out (thru). BTW. This is all out the window when considering tube components that require forced air cooling. Different situation entirely--and most use blowers not fans. FWIW Curt mike bryce wrote: thought I'd toss my .02 in with a question on the tr series, a fan mounted to the rear of the pa compartment, should it blow in or suck out? since we're not trying to pressurize a compartment, there's plenty of holes in the cage and top cover, and since heat rises, it would seem to me that one would mount the fan so it would blow into and onto the final tubes To me, it seems a fan sucking air out of the pa compartment would have to compete with the natural convention of heat raising so, what's the word from the thermal gods? Mike, WB8VGE SunLight Energy Systems The Heathkit Shop http://www.theheathkitshop.com/ J e e p o|||o If the facts don't fit the theory, change the facts. Albert Einstein ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
All: On both of my AC4s, from 1966ish, the cover has a series of slots along the top and lower edge just above the top of the chassis. These seem to provide a very even distribution of inlet air when using the method I have chosen. Are there AC4s that DO NOT have the slots? As Richard describes, if the slots aren't there, the suction cooling doesn't work. You have to have a way for the exchange air to enter. (Or escape) BTW, Richard is absolutely on target regarding the consideration of heat movement. No one cares about where the air goes we are really concerned about its effect on the heat flow. Thermal modeling and IR thermal imaging has provided designers today with much better analysis tools than were available in the 60's. Cheers Curt Richard Knoppow wrote: - Original Message - From: mike bryce proso...@sssnet.com To: Richard Knoppow 1oldle...@ix.netcom.com Cc: captc...@flash.net; Drakelist@zerobeat.net Sent: Thursday, December 16, 2010 9:32 AM Subject: Re: [Drakelist] AC4 heat Fan Summary thought I'd toss my .02 in with a question on the tr series, a fan mounted to the rear of the pa compartment, should it blow in or suck out? since we're not trying to pressurize a compartment, there's plenty of holes in the cage and top cover, and since heat rises, it would seem to me that one would mount the fan so it would blow into and onto the final tubes To me, it seems a fan sucking air out of the pa compartment would have to compete with the natural convention of heat raising so, what's the word from the thermal gods? Mike, WB8VGE SunLight Energy Systems The Heathkit Shop http://www.theheathkitshop.com/ I noted this in my little diatribe. For the T4 the fan works best sucking the heat out from the top. Its very simple and works. Most of the heat in this TX comes from the finals and is concentrated in the final compartment. While it is in a perforated metal enclosure there is a lot of heat generated in a small area plus the addition of the external cabinet further interferes with both direct radiation of heat and convection. A small fan very significantly reduces the heat. Much of what I wrote has to do with completely enclosed spaces where the conditions are quite different from the above. Where you can control the air flow there are advantages to positive pressure but, again, one must be careful to plot out the flow of _heat_ to insure one is not getting unintended heating rather than cooling. Actually, that's the problem with using a pushing fan on something like the T4, the heat is pushed out around other components and can heat them up where the sucking fan draws cool air from around the tubes and exhausts it directly to the air. I mainly wanted to point out the differences between cooling a basically open area like the T4 final cage and a completely enclosed space like the AC-4. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
- Original Message - From: Curt Nixon cptc...@flash.net Cc: Drakelist@zerobeat.net Sent: Thursday, December 16, 2010 10:59 AM Subject: Re: [Drakelist] AC4 heat Fan Summary All: On both of my AC4s, from 1966ish, the cover has a series of slots along the top and lower edge just above the top of the chassis. These seem to provide a very even distribution of inlet air when using the method I have chosen. Are there AC4s that DO NOT have the slots? As Richard describes, if the slots aren't there, the suction cooling doesn't work. You have to have a way for the exchange air to enter. (Or escape) BTW, Richard is absolutely on target regarding the consideration of heat movement. No one cares about where the air goes we are really concerned about its effect on the heat flow. Thermal modeling and IR thermal imaging has provided designers today with much better analysis tools than were available in the 60's. Cheers Curt Richard Knoppow wrote: - Original Message - From: mike bryce proso...@sssnet.com To: Richard Knoppow 1oldle...@ix.netcom.com Cc: captc...@flash.net; Drakelist@zerobeat.net Sent: Thursday, December 16, 2010 9:32 AM Subject: Re: [Drakelist] AC4 heat Fan Summary thought I'd toss my .02 in with a question on the tr series, a fan mounted to the rear of the pa compartment, should it blow in or suck out? since we're not trying to pressurize a compartment, there's plenty of holes in the cage and top cover, and since heat rises, it would seem to me that one would mount the fan so it would blow into and onto the final tubes To me, it seems a fan sucking air out of the pa compartment would have to compete with the natural convention of heat raising so, what's the word from the thermal gods? Mike, WB8VGE SunLight Energy Systems The Heathkit Shop http://www.theheathkitshop.com/ I noted this in my little diatribe. For the T4 the fan works best sucking the heat out from the top. Its very simple and works. Most of the heat in this TX comes from the finals and is concentrated in the final compartment. While it is in a perforated metal enclosure there is a lot of heat generated in a small area plus the addition of the external cabinet further interferes with both direct radiation of heat and convection. A small fan very significantly reduces the heat. Much of what I wrote has to do with completely enclosed spaces where the conditions are quite different from the above. Where you can control the air flow there are advantages to positive pressure but, again, one must be careful to plot out the flow of _heat_ to insure one is not getting unintended heating rather than cooling. Actually, that's the problem with using a pushing fan on something like the T4, the heat is pushed out around other components and can heat them up where the sucking fan draws cool air from around the tubes and exhausts it directly to the air. I mainly wanted to point out the differences between cooling a basically open area like the T4 final cage and a completely enclosed space like the AC-4. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
- Original Message - From: Curt Nixon cptc...@flash.net Cc: Drakelist@zerobeat.net Sent: Thursday, December 16, 2010 10:59 AM Subject: Re: [Drakelist] AC4 heat Fan Summary All: On both of my AC4s, from 1966ish, the cover has a series of slots along the top and lower edge just above the top of the chassis. These seem to provide a very even distribution of inlet air when using the method I have chosen. Are there AC4s that DO NOT have the slots? As Richard describes, if the slots aren't there, the suction cooling doesn't work. You have to have a way for the exchange air to enter. (Or escape) BTW, Richard is absolutely on target regarding the consideration of heat movement. No one cares about where the air goes we are really concerned about its effect on the heat flow. Thermal modeling and IR thermal imaging has provided designers today with much better analysis tools than were available in the 60's. Cheers Curt Sheesh... My AC-4 is maybe four feet away and I've rebuilt it. It DOES have the slots. I don't know why I pictured it with a completely solid case. All bets are off as far as my coments on blowing rather than sucking (oh dear) but I would put the fan so that air around the transformer is maximized. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
- Original Message - From: Curt Nixon cptc...@flash.net Cc: Drakelist@zerobeat.net Sent: Thursday, December 16, 2010 10:59 AM Subject: Re: [Drakelist] AC4 heat Fan Summary I evidently sent a blank reply to this message in the course of sending a real one. Not sure how I did that but I appologize. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] AC4 heat Fan Summary
On Thu, 16 Dec 2010 12:32:48 -0500, mike bryce wrote: should it blow in or suck out? This would seem to be a question of spot cooling vs. system cooling. You've already got some very good responses, so I'll keep this short. I did some experiments on this question RE: TR-7 a couple of years ago and confirmed that it was better to pull air out, rather than blow it in with the stock FA-7 fan. The most interesting result noted was that, with the fan blowing in, the temperature excursions in the area being spot cooled (the PA heatsink) were actually greater than with the fan pulling air out. Cooldown time was also longer. I don't know if this would hold true with the tube gear or power supply as well, or if it was just an anomaly related to the TR-7's heat sink design. 73 -Jim -- Ham Radio NU0C Lincoln, Nebraska, U.S.S.A. TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time! Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime. HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ http://radiojim.exofire.net http://incolor.inetnebr.com/jshorney http://www.nebraskaghosts.org ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
