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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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In for intermittant loss of one channel but this query is about overheating.
There are 5/8 inch high feet on the base but unless the owners prop up on blocks the whole base gets noticeably hot. I will be replacing the mains fan as 10 years of much use but any other observations from anyone familiar with them ? Dusty inside but not blocking any air throughput and no reported changes in fan noise and currently seems the correct sort of air flow for 14W fan. Design fault concerning airodynamics? There are 2 full width flutes of the heatsink that go up to the fan face. I would expect these bits of aluminium to be milled out normally in such situations. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#2
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![]() N_Cook wrote: In for intermittant loss of one channel but this query is about overheating. There are 5/8 inch high feet on the base but unless the owners prop up on blocks the whole base gets noticeably hot. I will be replacing the mains fan as 10 years of much use but any other observations from anyone familiar with them ? Dusty inside but not blocking any air throughput and no reported changes in fan noise and currently seems the correct sort of air flow for 14W fan. Design fault concerning airodynamics? There are 2 full width flutes of the heatsink that go up to the fan face. I would expect these bits of aluminium to be milled out normally in such situations. Is that the model that has a fan mounted horizontally blowing down onto a skimpy heatsink ? Graham |
#3
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Eeyore wrote in message
... N_Cook wrote: In for intermittant loss of one channel but this query is about overheating. There are 5/8 inch high feet on the base but unless the owners prop up on blocks the whole base gets noticeably hot. I will be replacing the mains fan as 10 years of much use but any other observations from anyone familiar with them ? Dusty inside but not blocking any air throughput and no reported changes in fan noise and currently seems the correct sort of air flow for 14W fan. Design fault concerning airodynamics? There are 2 full width flutes of the heatsink that go up to the fan face. I would expect these bits of aluminium to be milled out normally in such situations. Is that the model that has a fan mounted horizontally blowing down onto a skimpy heatsink ? Graham Blowing up into an adequate , for fan blown, heatsink with a bank of 12 motorola 70483080 TO3 . As far as I can see the 2 uncut-down heatsink vanes that go across the fan do little functionally for cooling and probably disrupt the air flow. The air has to come in horizontally under the base , up the one inch of fan axis and then have to abruptly divert horizontally again down the 2 (separated by these vanes) relatively small channels in the heatsink. I'll take a pic perhaps -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#4
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Perhaps the sensible approach to this is extend the rubber feet by half an
inch as this is a known cure. There is no obvious place to put a secoind fan at the air outlet. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#5
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Meat Plow wrote in message
... On Wed, 28 May 2008 18:31:00 +0100, N_Cook wrote: Perhaps the sensible approach to this is extend the rubber feet by half an inch as this is a known cure. There is no obvious place to put a secoind fan at the air outlet. So every XR 886 overheats? Not to the extent of tripping any of the thermal switches but enough to concern the owner into trying to improve airflow - admirable thinking for a non-techie. Just giving greater clearance to the airflow under an amp should not normally affect the amp temperature though. I would suggest that it is due to forcing the air to follow a tortuous path so a generic design flaw. I've heated up the fan motor, etc and there seems nothing wrong with this fan as well as no change of fan noise reported by the owner. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#6
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N_Cook wrote:
Meat Plow wrote in message ... On Wed, 28 May 2008 18:31:00 +0100, N_Cook wrote: Perhaps the sensible approach to this is extend the rubber feet by half an inch as this is a known cure. There is no obvious place to put a secoind fan at the air outlet. So every XR 886 overheats? Not to the extent of tripping any of the thermal switches but enough to concern the owner into trying to improve airflow - admirable thinking for a non-techie. Just giving greater clearance to the airflow under an amp should not normally affect the amp temperature though. I would suggest that it is due to forcing the air to follow a tortuous path so a generic design flaw. I've heated up the fan motor, etc and there seems nothing wrong with this fan as well as no change of fan noise reported by the owner. What say if an amplifier was designed in such a way that the thermal protection was intended to operate at some given device temperature, say the safe working temp of the output transistors, and the cooling arrangments designed accordingly? Output transistors get hot, heatsink gets hot, thermal devices trip, amplifier shuts down or whatever it`s designed to do. But, by increasing the airflow from the fan[1] or improving the cooling to the heatsink in some other way, results in the heatsink remaining cooler when the actual output devices themselves are still running at a high temperature. Bearing in mind that the temp sensors may not be directly monitoring the devices temp, but some other area on the heatsink, that might lead to the thermal protection failing to operate. By changing the design of the cooling, you could be blowing cool air over the temp sensors and not the output devices. Result = a trip to silicon heaven. I have seen Peavey mixer amps shut down in hot weather when placed in direct sunlight and driven hard, that`s the protection doing what it`s designed to do tho. Generally speaking, if a decent quality amplifier is overheating, it`s operator error, not a design fault. (IMO) Ron(UK) [1] This is hypothetical of course, I realise you havent changed the fan or it`s cooling path in this instance, but I think it`s something to be aware of. Maybe someone with experience in 'designing' power amplifiers could comment? |
#7
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Ron(UK) wrote in message
... N_Cook wrote: Meat Plow wrote in message ... On Wed, 28 May 2008 18:31:00 +0100, N_Cook wrote: Perhaps the sensible approach to this is extend the rubber feet by half an inch as this is a known cure. There is no obvious place to put a secoind fan at the air outlet. So every XR 886 overheats? Not to the extent of tripping any of the thermal switches but enough to concern the owner into trying to improve airflow - admirable thinking for a non-techie. Just giving greater clearance to the airflow under an amp should not normally affect the amp temperature though. I would suggest that it is due to forcing the air to follow a tortuous path so a generic design flaw. I've heated up the fan motor, etc and there seems nothing wrong with this fan as well as no change of fan noise reported by the owner. What say if an amplifier was designed in such a way that the thermal protection was intended to operate at some given device temperature, say the safe working temp of the output transistors, and the cooling arrangments designed accordingly? Output transistors get hot, heatsink gets hot, thermal devices trip, amplifier shuts down or whatever it`s designed to do. But, by increasing the airflow from the fan[1] or improving the cooling to the heatsink in some other way, results in the heatsink remaining cooler when the actual output devices themselves are still running at a high temperature. Bearing in mind that the temp sensors may not be directly monitoring the devices temp, but some other area on the heatsink, that might lead to the thermal protection failing to operate. By changing the design of the cooling, you could be blowing cool air over the temp sensors and not the output devices. Result = a trip to silicon heaven. I have seen Peavey mixer amps shut down in hot weather when placed in direct sunlight and driven hard, that`s the protection doing what it`s designed to do tho. Generally speaking, if a decent quality amplifier is overheating, it`s operator error, not a design fault. (IMO) Ron(UK) [1] This is hypothetical of course, I realise you havent changed the fan or it`s cooling path in this instance, but I think it`s something to be aware of. Maybe someone with experience in 'designing' power amplifiers could comment? s.e.d added All very true but you seem to be missing the point. An amp that works perfectly all right should not suddenly run noticeably cooler doing exactly the same job in the same gig but just placing fag packets, lighters etc , whatever was at hand, under each of the feet on the base. 2 th sw on 2 of the o/p TO3 and one on the heatsink in this case and yes the air blows over the those 2 th sw as much as the cans of the TO3, in fact they are directly in the ducted flow of air probably reducing the passing volume/area by a 1/3 at each end of one of the heatsink ducts, compared to no th sw in the path. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#8
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![]() N_Cook wrote: Eeyore wrote in message Is that the model that has a fan mounted horizontally blowing down onto a skimpy heatsink ? Blowing up into an adequate , for fan blown, heatsink with a bank of 12 motorola 70483080 TO3 How do you define adequate ? I design my own heatsinks for amps you see and most others I come across are very inadequate, notably recent Peaveys. Graham |
#9
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![]() N_Cook wrote: Perhaps the sensible approach to this is extend the rubber feet by half an inch as this is a known cure. A simple solution at least. There is no obvious place to put a secoind fan at the air outlet. You CAN 'gang' 2 fans in series to increase the air pressure but I've never needed to do it. Also, fitting a 'thicker' fan will increase the air pressure. You may find 12, 19 and 25mm versions of certain axial fans. The thicker they get, the more pressure they generate and that helps achieve good airflow. The CFM figures are largely just a guidline since there are with zero pressure gradient. Graham |
#10
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![]() Meat Plow wrote: N_Cook wrote: Perhaps the sensible approach to this is extend the rubber feet by half an inch as this is a known cure. There is no obvious place to put a secoind fan at the air outlet. So every XR 886 overheats? Would depend how they're operated, load impedance and the style of music (especially so). I have researched this area extensively and the variations are enormous.Stnadardised tests such as 1/8 or 1/3 power noise are especially useless. Graham |
#11
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![]() N_Cook wrote: Just giving greater clearance to the airflow under an amp should not normally affect the amp temperature though. Yes it will by reducing the back pressure. Graham |
#12
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![]() N_Cook wrote: I would suggest that it is due to forcing the air to follow a tortuous path so a generic design flaw. That's what causes the high back pressure (and hence low air flow). For good cooling the airflow path should be in a striaght line with air vents in and out as large as possible (consistent with safety regs) and there are some other cute aspects which are even less well known too. Graham |
#13
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Eeyore wrote in message
... N_Cook wrote: Eeyore wrote in message Is that the model that has a fan mounted horizontally blowing down onto a skimpy heatsink ? Blowing up into an adequate , for fan blown, heatsink with a bank of 12 motorola 70483080 TO3 How do you define adequate ? I design my own heatsinks for amps you see and most others I come across are very inadequate, notably recent Peaveys. Graham For fan blown o/p devices the heatsink surely does not have to be much more that a metal matrix for holding the devices to. Does not have to be multifluted or with those chisseled multi-vanes etc (sorry don't know the generic term , end up curved ) or a great mass of metal for convection cooling -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#14
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Eeyore wrote in message
... N_Cook wrote: I would suggest that it is due to forcing the air to follow a tortuous path so a generic design flaw. That's what causes the high back pressure (and hence low air flow). For good cooling the airflow path should be in a striaght line with air vents in and out as large as possible (consistent with safety regs) and there are some other cute aspects which are even less well known too. Graham Agreed , I'll take a photo later to show how tortuous this path is. Even more dramatic was an Ashdown amp I had to repair recently for another fault. Supposedly fan assisted cooling but the fan "design" location was just circulating air inside the casing as no baffles etc to guide air in and out the single "vent" port. Owner much appreciated the amp running much cooler and being able to feel air coming out of the vent. s.e.r added as design issue -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#15
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![]() "Ron(UK)" wrote: Maybe someone with experience in 'designing' power amplifiers could comment? I have done ! There's something worth adding though. To optmise air flow you need a high 'static pressure'. There's a huge variation in this characteristic. The best examples I've found are NMB (formerly Boxer) and Panasonic's Panaflow fans. Be careful to order the high pressure version. They make versions with various motors speeds. In the case of NMB, the 'best' ones used to have 'B50' as part of the part number. I forget Panasonic's method of marking. DO NOT use cheap 'off brand' fans for applications like this. I see Farnell have NMB but only as a special US import. You didn't say what size it is but the popular 80mm size would be for example .... http://uk.farnell.com/8235414/electr...kl-05w-b50-e00 Read the data sheet here http://www.eminebea.com/content/pdf/...3/I/3112kl.pdf to see just how radically. the airflow varies with the Bxx model number. Graham |
#16
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![]() N_Cook wrote: An amp that works perfectly all right should not suddenly run noticeably cooler doing exactly the same job in the same gig but just placing fag packets, lighters etc , whatever was at hand, under each of the feet on the base. You don't understand equipment cooling adequately. It's PERFECTLY obvious to me. It's all to do with the effect of back pressure on air flow. Adding more space underneath the unit reduces the back pressure. It's a truly cruddy design that they did it that way though. Graham |
#17
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![]() N_Cook wrote: For fan blown o/p devices the heatsink surely does not have to be much more that a metal matrix for holding the devices to. The larger area the better. Does not have to be multifluted That certainly helps. or with those chisseled multi-vanes etc (sorry don't know the generic term , end up curved ) Those increase surface area which is a GOOD THING. or a great mass of metal for convection cooling It most certainly DOES NOT need to have great weight. But almost none of the colling in SR amp is classic convection anyway. What typically helps is maximum surface area of the fins/vanes to create the best opportunity to let the heat transfer to the air flow, but you can improve even that by 'slotting' the 'vanes' to create a slightly turbulent air flow. Trust me I could write a lecture on the subject. Graham |
#18
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Eeyore wrote:
N_Cook wrote: For fan blown o/p devices the heatsink surely does not have to be much more that a metal matrix for holding the devices to. The larger area the better. Does not have to be multifluted That certainly helps. or with those chisseled multi-vanes etc (sorry don't know the generic term , end up curved ) Those increase surface area which is a GOOD THING. or a great mass of metal for convection cooling It most certainly DOES NOT need to have great weight. But almost none of the colling in SR amp is classic convection anyway. What typically helps is maximum surface area of the fins/vanes to create the best opportunity to let the heat transfer to the air flow, but you can improve even that by 'slotting' the 'vanes' to create a slightly turbulent air flow. Trust me I could write a lecture on the subject. I recall many years ago that there was a 'manufacturers mod' for some power amp or other ( dont recall which) where you had to bend all the vanes of the heatsinks - which were like combs - away from the vertical in various different directions to improve the marginal cooling just that tiny bit to prevent the thermal protection tripping. Looked damn ugly but did the trick. What works best Graham, a thick ally heatsink with many thick fins, or a thick ally plate with many convoluted thin sheet fins? Ron |
#19
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Eeyore wrote in message
... N_Cook wrote: For fan blown o/p devices the heatsink surely does not have to be much more that a metal matrix for holding the devices to. The larger area the better. Does not have to be multifluted That certainly helps. or with those chisseled multi-vanes etc (sorry don't know the generic term , end up curved ) Those increase surface area which is a GOOD THING. or a great mass of metal for convection cooling It most certainly DOES NOT need to have great weight. But almost none of the colling in SR amp is classic convection anyway. What typically helps is maximum surface area of the fins/vanes to create the best opportunity to let the heat transfer to the air flow, but you can improve even that by 'slotting' the 'vanes' to create a slightly turbulent air flow. Trust me I could write a lecture on the subject. Graham Anyone know the generic name for this type of what I assume is chisel-action-cut vaned heatsink. Is it made using a shaper type machine with some sort of chisel or plane blade? http://home.graffiti.net/diverse:gra...e_heatsink.jpg -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#20
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This is the amp in question
http://home.graffiti.net/diverse:gra...net/peavey.jpg Yellow ring stands in for the 4 inch fan removed (position marked with Fs )along with metal sheet that encloses the heatsink. The view of this amp is upside down as the fan is at the base. So drawing air horizonatally theough a "designed" 5/8 inch space under the amp. Air then goes through the 1 in of fan vertically and then has to sharply divert horizontally to flow either way through the 3 ducts in each direction. The central duct contains no active ducts and as far as I can see only interferes with air flow as they are right up against the fan housing. Air then vents mainly at either end when the metal closure in place with not enough space to add a fan or 2 at those points and nowhere near the mains transformer and main air outlet vent . A lot of venting must go up and out the mixer pannel slider holes etc as well. The 2 TO3 mounted thermal switches are marked S and restrict the air flow through the uppermost duct in the pic, the leads and spades as much as the switch body -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#21
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N_Cook wrote:
This is the amp in question http://home.graffiti.net/diverse:gra...net/peavey.jpg Yellow ring stands in for the 4 inch fan removed (position marked with Fs )along with metal sheet that encloses the heatsink. The view of this amp is upside down as the fan is at the base. So drawing air horizonatally theough a "designed" 5/8 inch space under the amp. Air then goes through the 1 in of fan vertically and then has to sharply divert horizontally to flow either way through the 3 ducts in each direction. The central duct contains no active ducts and as far as I can see only interferes with air flow as they are right up against the fan housing. Air then vents mainly at either end when the metal closure in place with not enough space to add a fan or 2 at those points and nowhere near the mains transformer and main air outlet vent . A lot of venting must go up and out the mixer pannel slider holes etc as well. The 2 TO3 mounted thermal switches are marked S and restrict the air flow through the uppermost duct in the pic, the leads and spades as much as the switch body I think that the worst part of that desgn IIRC is that the board is mounted inverted with the sinks beneath, thus any heat which tried to escape by convection has to pass through the pcb, heating the other components. Am I correct in that assumption? Ron |
#22
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![]() "Ron(UK)" wrote: Eeyore wrote: N_Cook wrote: For fan blown o/p devices the heatsink surely does not have to be much more that a metal matrix for holding the devices to. The larger area the better. Does not have to be multifluted That certainly helps. or with those chisseled multi-vanes etc (sorry don't know the generic term , end up curved ) Those increase surface area which is a GOOD THING. or a great mass of metal for convection cooling It most certainly DOES NOT need to have great weight. But almost none of the cooling in SR amps is classic convection anyway. What typically helps is maximum surface area of the fins/vanes to create the best opportunity to let the heat transfer to the air flow, but you can improve even that by 'slotting' the 'vanes' to create a slightly turbulent air flow. You can btw see this in many 'CPU cooler' designs. However it can cause dust and fluff to collect. Trust me I could write a lecture on the subject. I recall many years ago that there was a 'manufacturers mod' for some power amp or other ( dont recall which) where you had to bend all the vanes of the heatsinks - which were like combs - away from the vertical in various different directions to improve the marginal cooling just that tiny bit to prevent the thermal protection tripping. Looked damn ugly but did the trick. Yes I can believe that. It would help cause the 'turbulent airflow' effect. I first learnt about this around 30 years ago from data supplied by the IERC heatsink company and have widely used the technique ever since with measurable success. You see with purely vertical or horizontal fins widely spaced, the air going 'up the middle' between them never actually extracts much useful heat. You need to get the airflow to 'mix' to get the best effect. What works best Graham, a thick ally heatsink with many thick fins, or a thick ally plate with many convoluted thin sheet fins? Within reason, the fins don't need to be that thick at all. Their minimum width is normally a limitation of the extrusion technique. What's best it have lots of them, consistent with not creating a dust trap by having them pitched too fine.. Don't make the fins TOO convoluted as this will actually impede airflow. I have my own 'proprietary' technique that avoids any need to twist the fins which most people would find counter-intuitive but in a calibrated test produced a 20% improvement in thermal resistance with a lower weight of aluminium in 2 (superficially to the casual viewer) identical designs. As it seems no-one has yet twigged my method, I'm reluctant to give away my 'secret'. As for the 'plate' its needs to be thickest near the devices and can taper further out. Thermal resistance calculation are little different to electrical resistance after all. Graham |
#23
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![]() N_Cook wrote: Anyone know the generic name for this type of what I assume is chisel-action-cut vaned heatsink. Is it made using a shaper type machine with some sort of chisel or plane blade? http://home.graffiti.net/diverse:gra...e_heatsink.jpg I'm afraid I found the pic too unclear to be sure what I was looking at. Is it formed from sheet aluminium ? Graham |
#24
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![]() N_Cook wrote: This is the amp in question http://home.graffiti.net/diverse:gra...net/peavey.jpg That is about the worst excuse for a 'heatsink' I have seen in my entire life. It's utterly pathetic. In fact it's completely WRONG in just about every way possible. I have seen another that came close to being that bad but even so at least there were a few more vanes on it (C-Audio btw). The company I was with was considering taking the C-Audio design as a OEM product and re-branding it, but my tests showed a heatsink temp of up to 150C with a 40C ambient on music test signal. This was enough to cause several of the output mosfets to fail open-circuit and I only realised that when later bench testing it and finding asymmetrical clipping. After declining their offer of the product I later found they'd added more heatsinking but it was a kludge. Just for good measure, C-Audio also exhausted the searingly hot air right over the PSU electrolytics ! These were well known to need regular replacement which C-Audio justified as they said they were a 'service item'. My own designs (including one in the local venue) are known for working day in, day out for years on end. I think the one in there is getting on for 10 years old now and is used every night although not every night is a 'loud' band. It has had a 'blow through' or two of the heatsinks and 2 new level pots (only one went crackly but it's best to replace both whilst you're at it, and yes, they're NOT pcb mounted so it's an easy job too. Compare that with a QSC RMX 2450 I also had to do the same to (labour time approx 4:1 ratio). I never fail to be amazed at the number of amps that illustrate that the designers are completely incompetent when it comes to thermal management. And don't even get me started on power transformer design ! Graham |
#25
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![]() N_Cook wrote: The view of this amp is upside down as the fan is at the base. So drawing air horizonatally theough a "designed" 5/8 inch space under the amp. Hahahahahahahaa ! What LOONIES. That's STALLING the fan blades. NO wonder putting bigger feet on helps. How well would a propellor aircraft fly if you put an obstruction in front of the prop ? Graham |
#26
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Ron(UK) wrote in message
... N_Cook wrote: This is the amp in question http://home.graffiti.net/diverse:gra...net/peavey.jpg Yellow ring stands in for the 4 inch fan removed (position marked with Fs )along with metal sheet that encloses the heatsink. The view of this amp is upside down as the fan is at the base. So drawing air horizonatally theough a "designed" 5/8 inch space under the amp. Air then goes through the 1 in of fan vertically and then has to sharply divert horizontally to flow either way through the 3 ducts in each direction. The central duct contains no active ducts and as far as I can see only interferes with air flow as they are right up against the fan housing. Air then vents mainly at either end when the metal closure in place with not enough space to add a fan or 2 at those points and nowhere near the mains transformer and main air outlet vent . A lot of venting must go up and out the mixer pannel slider holes etc as well. The 2 TO3 mounted thermal switches are marked S and restrict the air flow through the uppermost duct in the pic, the leads and spades as much as the switch body I think that the worst part of that desgn IIRC is that the board is mounted inverted with the sinks beneath, thus any heat which tried to escape by convection has to pass through the pcb, heating the other components. Am I correct in that assumption? Ron The heatsink is fitted onto the pcb that caries nothing on that area but holds a lot of ceramic W/W seen either side on the pic, usefully, I suppose, in the airflow. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#27
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Eeyore wrote in message
... N_Cook wrote: Anyone know the generic name for this type of what I assume is chisel-action-cut vaned heatsink. Is it made using a shaper type machine with some sort of chisel or plane blade? http://home.graffiti.net/diverse:gra...e_heatsink.jpg I'm afraid I found the pic too unclear to be sure what I was looking at. Is it formed from sheet aluminium ? Graham I was rushing around a didn't focus on the right distance. Will have another go closer up , showing the chisel? cuts. Could not find an image of one out there. Often seen in Sony domestic amps of the 70s/80s TA..., STR...all convection cooled The cutting action must be like those butter or cheese knives/scoops that curl the material into whirls -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#28
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Eeyore wrote in message
... N_Cook wrote: The view of this amp is upside down as the fan is at the base. So drawing air horizonatally theough a "designed" 5/8 inch space under the amp. Hahahahahahahaa ! What LOONIES. That's STALLING the fan blades. NO wonder putting bigger feet on helps. How well would a propellor aircraft fly if you put an obstruction in front of the prop ? Graham Expressing it like that highlights the flaw admirably. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#29
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A better pic , without yellow ring is now at
http://home.graffiti.net/diverse:gra...net/peavey.jpg -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#30
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A better pic is now on
http://home.graffiti.net/diverse:gra...e_heatsink.jpg plus a close up showing the slightly angled cuts http://home.graffiti.net/diverse:gra..._heatsink2.jpg -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#31
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That ancient Peavey transformer might be hotter (thermally! not
wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst case power at about 1/3rd max power.... its where the load line runs right across the hyperbola on the IV curve... and if the voltage in the club sags when the drink cooler compressor turns on, its a perfect storm of overheat factors. |
#32
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BobG wrote:
That ancient Peavey transformer might be hotter (thermally! not wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst case power at about 1/3rd max power.... its where the load line runs right across the hyperbola on the IV curve... and if the voltage in the club sags when the drink cooler compressor turns on, its a perfect storm of overheat factors. Voltages in the UK don`t generally sag much if at all Ron |
#33
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On May 29, 2:35*pm, "Ron(UK)" wrote:
Voltages in the UK don`t generally sag much if at all ============================================= Is that in percent or in volts? I've glanced at the power line monitor during the end of a song and seen 105V... should be 120, but with lights and air conditioners and everything else, 115 is more like the nominal. So that 10% low. |
#34
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BobG wrote:
On May 29, 2:35 pm, "Ron(UK)" wrote: Voltages in the UK don`t generally sag much if at all ============================================= Is that in percent or in volts? I've glanced at the power line monitor during the end of a song and seen 105V... should be 120, but with lights and air conditioners and everything else, 115 is more like the nominal. So that 10% low. Our mains supply is 240 volts |
#35
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![]() "Ron(UK)" wrote in message ... BobG wrote: That ancient Peavey transformer might be hotter (thermally! not wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst case power at about 1/3rd max power.... its where the load line runs right across the hyperbola on the IV curve... and if the voltage in the club sags when the drink cooler compressor turns on, its a perfect storm of overheat factors. Voltages in the UK don`t generally sag much if at all Ron AFAIK the lowest legal voltage the electricity company can supply in the UK is 10% down (from 240) which is 216v, the highest legal voltage is 254v, less that 6% high. Suffice to say you won't normally get those kind of variations at the mains intake at the venue. I don't know how much voltage drop you might experience due to the clubs wiring before it was deemed unsafe or illegal though. Gareth. |
#36
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![]() "Ron(UK)" wrote: BobG wrote: That ancient Peavey transformer might be hotter (thermally! not wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst case power at about 1/3rd max power.... its where the load line runs right across the hyperbola on the IV curve... and if the voltage in the club sags when the drink cooler compressor turns on, its a perfect storm of overheat factors. Voltages in the UK don`t generally sag much if at all You beat me to it. Graham |
#37
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![]() BobG wrote: On May 29, 2:35 pm, "Ron(UK)" wrote: Voltages in the UK don`t generally sag much if at all ============================================= Is that in percent or in volts? Whatever you like Graham |
#38
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![]() gareth magennis wrote: "Ron(UK)" wrote BobG wrote: That ancient Peavey transformer might be hotter (thermally! not wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst case power at about 1/3rd max power.... its where the load line runs right across the hyperbola on the IV curve... and if the voltage in the club sags when the drink cooler compressor turns on, its a perfect storm of overheat factors. Voltages in the UK don`t generally sag much if at all AFAIK the lowest legal voltage the electricity company can supply in the UK is 10% down (from 240) which is 216v, the highest legal voltage is 254v, less that 6% high. It won't be based on 240V any more because we're officially (on paper) 230V. Maybe 230 +/- 10% but that's just an EU standard - it's NEVER as low as that. Suffice to say you won't normally get those kind of variations at the mains intake at the venue. I don't know how much voltage drop you might experience due to the clubs wiring before it was deemed unsafe or illegal though. Never seen any worth talking about. Have you ? Graham |
#39
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![]() "Eeyore" wrote in message ... gareth magennis wrote: "Ron(UK)" wrote BobG wrote: That ancient Peavey transformer might be hotter (thermally! not wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst case power at about 1/3rd max power.... its where the load line runs right across the hyperbola on the IV curve... and if the voltage in the club sags when the drink cooler compressor turns on, its a perfect storm of overheat factors. Voltages in the UK don`t generally sag much if at all AFAIK the lowest legal voltage the electricity company can supply in the UK is 10% down (from 240) which is 216v, the highest legal voltage is 254v, less that 6% high. It won't be based on 240V any more because we're officially (on paper) 230V. Maybe 230 +/- 10% but that's just an EU standard - it's NEVER as low as that. On paper maybe, but in practice its still pretty much 240v. Suffice to say you won't normally get those kind of variations at the mains intake at the venue. I don't know how much voltage drop you might experience due to the clubs wiring before it was deemed unsafe or illegal though. Never seen any worth talking about. Have you ? Graham No, I put that down to good wiring regulations. (I remember when I was in a function band and we used to play the Forces bases in Germany with dodgy old 220v domestic-at-best wiring. We only had about a 3K system but often had to carefully switch the amps on one at a time to stop the breakers tripping, then all the house lights and all the gears' illumination would dim in time to the kick drum. Frightening really. None of my keyboards ever crashed though.) So what would be the maximum voltage drop you might expect from a non overloaded mains system? Gareth. |
#40
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![]() gareth magennis wrote: So what would be the maximum voltage drop you might expect from a non overloaded mains system? Crikey. I know where I'd test with a highish power PA rig, the local venue that has some 5kW ? or so of amps but last year I had a separate 32A circuit run in just for the amp rack so I doubt it would be more than a few volts. Graham |
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