HK Audio Actor / Lucas power amps , generic problem?
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From: Gareth Magennis on 7 Jan 2010 04:50 "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message news:oWb1n.11179$mQ.2517(a)newsfe01.ams2... > > "N_Cook" <diverse(a)tcp.co.uk> wrote in message > news:hi1o7d$fic$1(a)news.eternal-september.org... >> >> 20 degrees is about the most or you block off access to the TO3s. Maybe >> only >> tinkering at the heat build up problem. Most air must go through the 25mm >> or >> so wide gap in the ps direction (over the tips of the vanes), rather than >> the 2 off 5mm gaps to the duct let alone through all those vanes. I >> would >> have thought there should be some shuttering to block off most of that >> large >> gap along the ps side , to force most air round and through the >> heatsinks. >> >> They were assembled with enough white goo to keep a goth happy for a >> week. >> So much that she filled the B & E holes so pins pushed through it, not >> cleaned off, and some white goo actually under the solder joints (not >> actually failures there). Those failed caps 47uF, 63V - in similar HK amp >> they were rated 40V 47uF , what is the problem in that area of the >> circuit? >> >> >> > > On reflection, I don't think that these are actually designed with 'forced > air' cooling in mind. Rather, I think that that type of heatsink is > intended to suck the heat off the transistors, and then radiate it to free > air, and that the purpose of the fan is to shift new cool air through the > chassis / cabinet, to help the radiation take place. When the air intakes > get clogged, the internal ambient temperature goes up, stopping the > radiation from taking place efficiently, with a consequent large rise in > the case temperature of the transistor, made worse by the dried out > thermal paste. > > I don't quite agree with Gareth that the heatsinking is inadequate. I > think it is just about adequate, as long as the designed level of airflow > around the chassis can be maintained. If it can't by virtue of the intakes > being clogged, then it becomes very marginal. > > However, I suppose it could be argued that it is 'inadequate' in that > there is little or no margin built in for compromised airflow. > > Arfa > That was my definition of inadequate. The fact that 3 of us here have seen large quantities of the same units with the exact same problems bear this out. I'm sure we've all seen plenty of amplifiers with a whole ton of dust inside that have been working hard for years. I had a theory that because once repaired they tend not to come back, this may point to either a manufacturing issue or dodgy batch of Darlingtons (?) Gareth.
From: Gareth Magennis on 7 Jan 2010 04:56 "Gareth Magennis" <sound.service(a)btconnect.com> wrote in message news:E7i1n.3069$2F5.2098(a)newsfe07.ams2... > > > "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message > news:oWb1n.11179$mQ.2517(a)newsfe01.ams2... >> >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message >> news:hi1o7d$fic$1(a)news.eternal-september.org... >>> >>> 20 degrees is about the most or you block off access to the TO3s. Maybe >>> only >>> tinkering at the heat build up problem. Most air must go through the >>> 25mm or >>> so wide gap in the ps direction (over the tips of the vanes), rather >>> than >>> the 2 off 5mm gaps to the duct let alone through all those vanes. I >>> would >>> have thought there should be some shuttering to block off most of that >>> large >>> gap along the ps side , to force most air round and through the >>> heatsinks. >>> >>> They were assembled with enough white goo to keep a goth happy for a >>> week. >>> So much that she filled the B & E holes so pins pushed through it, not >>> cleaned off, and some white goo actually under the solder joints (not >>> actually failures there). Those failed caps 47uF, 63V - in similar HK >>> amp >>> they were rated 40V 47uF , what is the problem in that area of the >>> circuit? >>> >>> >>> >> >> On reflection, I don't think that these are actually designed with >> 'forced air' cooling in mind. Rather, I think that that type of heatsink >> is intended to suck the heat off the transistors, and then radiate it to >> free air, and that the purpose of the fan is to shift new cool air >> through the chassis / cabinet, to help the radiation take place. When the >> air intakes get clogged, the internal ambient temperature goes up, >> stopping the radiation from taking place efficiently, with a consequent >> large rise in the case temperature of the transistor, made worse by the >> dried out thermal paste. >> >> I don't quite agree with Gareth that the heatsinking is inadequate. I >> think it is just about adequate, as long as the designed level of airflow >> around the chassis can be maintained. If it can't by virtue of the >> intakes being clogged, then it becomes very marginal. >> >> However, I suppose it could be argued that it is 'inadequate' in that >> there is little or no margin built in for compromised airflow. >> >> Arfa >> > > > That was my definition of inadequate. The fact that 3 of us here have > seen large quantities of the same units with the exact same problems bear > this out. > I'm sure we've all seen plenty of amplifiers with a whole ton of dust > inside that have been working hard for years. > > I had a theory that because once repaired they tend not to come back, this > may point to either a manufacturing issue or dodgy batch of Darlingtons > (?) > > > > Gareth. > > Oh, BTW, can you confirm which way the fans run? Sucking air out the cabinet or blowing it in? Gareth.
From: Ron on 7 Jan 2010 05:47 On 07/01/2010 02:46, Arfa Daily wrote: > "N_Cook"<diverse(a)tcp.co.uk> wrote in message > news:hi1o7d$fic$1(a)news.eternal-september.org... >> >> 20 degrees is about the most or you block off access to the TO3s. Maybe >> only >> tinkering at the heat build up problem. Most air must go through the 25mm >> or >> so wide gap in the ps direction (over the tips of the vanes), rather than >> the 2 off 5mm gaps to the duct let alone through all those vanes. I would >> have thought there should be some shuttering to block off most of that >> large >> gap along the ps side , to force most air round and through the heatsinks. >> >> They were assembled with enough white goo to keep a goth happy for a week. >> So much that she filled the B& E holes so pins pushed through it, not >> cleaned off, and some white goo actually under the solder joints (not >> actually failures there). Those failed caps 47uF, 63V - in similar HK amp >> they were rated 40V 47uF , what is the problem in that area of the >> circuit? >> >> >> > > On reflection, I don't think that these are actually designed with 'forced > air' cooling in mind. Rather, I think that that type of heatsink is intended > to suck the heat off the transistors, and then radiate it to free air, and > that the purpose of the fan is to shift new cool air through the chassis / > cabinet, to help the radiation take place. When the air intakes get clogged, > the internal ambient temperature goes up, stopping the radiation from taking > place efficiently, with a consequent large rise in the case temperature of > the transistor, made worse by the dried out thermal paste. > > I don't quite agree with Gareth that the heatsinking is inadequate. I think > it is just about adequate, as long as the designed level of airflow around > the chassis can be maintained. If it can't by virtue of the intakes being > clogged, then it becomes very marginal. > > However, I suppose it could be argued that it is 'inadequate' in that there > is little or no margin built in for compromised airflow. > > Arfa > I suspect usage has a bit to do with it also. The Eliot/Lucas were never intended for 'Heavy Metal' or bass heavy dance music. Prolonged thrashing is probably what heats them up. Another thing, they don't like having the satellite speaker plugged and unplugged while drive is applied, I`ve fixed more than one where the owner admitted that`s what happened. Ron
From: N_Cook on 7 Jan 2010 07:40 Gareth Magennis <sound.service(a)btconnect.com> wrote in message news:0di1n.3070$2F5.2360(a)newsfe07.ams2... > > > "Gareth Magennis" <sound.service(a)btconnect.com> wrote in message > news:E7i1n.3069$2F5.2098(a)newsfe07.ams2... > > > > > > "Arfa Daily" <arfa.daily(a)ntlworld.com> wrote in message > > news:oWb1n.11179$mQ.2517(a)newsfe01.ams2... > >> > >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >> news:hi1o7d$fic$1(a)news.eternal-september.org... > >>> > >>> 20 degrees is about the most or you block off access to the TO3s. Maybe > >>> only > >>> tinkering at the heat build up problem. Most air must go through the > > Oh, BTW, can you confirm which way the fans run? Sucking air out the > cabinet or blowing it in? > > > > Gareth. > This one is outwards 4,000 sq mm of purpose built inlet holes and 3,300 sq mm through fan vent I would have thought was quite adequate if the air was directed over the heatsinks and not wind-breaked. This one permanent mounted high up away from floor dust. Compared with Laney CD850 , totally inadequate constriction on outlet over fan . 3 of those I've cut away the "vent" holes over the fan, fared off and covered with a wire grille and they've not bounced back (each was cutting out thermally after extended but normal use) As the Laney original design just 14 small slots with a combined area of only 1.5 sq inches, let alone vortexing, so overloading the 3 inch diameter fan with through ducted area of about 6 sq ins , ridiculous aerodynamics
From: N_Cook on 7 Jan 2010 10:01
Gareth Magennis <sound.service(a)btconnect.com> wrote in message news:Af61n.20179$AV4.16792(a)newsfe04.ams2... > > > "Ron" <ron(a)lunevalleyaudio.com> wrote in message > news:FMWdnar5p5rYhd7WnZ2dnUVZ8nGdnZ2d(a)bt.com... > > On 05/01/2010 09:59, Arfa Daily wrote: > >> "N_Cook"<diverse(a)tcp.co.uk> wrote in message > >> news:hhv006$kqa$1(a)news.eternal-september.org... > >>> They have an otherwise original assembly method of the final contact to > >>> the > >>> pins of TO3 power transistors by 2 zero ohm "resistor" links, so 2 > >>> current > >>> paths to the pcb traces. Anyone else observed bad solder joints to these > >>> links on the pcb? and cause? believed conventional solder not PbF > >>> > >>> > >>> > >>> > >> > >> I repair many of these, and can honestly say that I have *never* observed > >> any bad joints at the place you mention. By far the commonest problem is > >> failed output transistors. This occurs because the heatsinks are only > >> just > >> about adequate with proper cooling. As soon as the fan air intake vents > >> start to clog up with fluff, the outputs start to run too hot. Over a > >> period > >> of time, this dries out the heatsink paste to a powder, leading > >> ultimately > >> to transistor failure. > >> > >> Whenever I get one, I always remove the other pair of transistors as > >> well, > >> clean down their heatsinks, and re-paste them, not forgetting the flatpak > >> transistor that's in contact with the underside of one heatsink on each > >> channel. > >> > >> The manufacturers recommend that when the outputs are replaced, two of > >> the > >> BC546Bs nearby are replaced as well (T7 / 8 on one channel, 10 / 11 on > >> the > >> other). Check also C3 and C21 to make sure that they are not bulging. > >> > >> Other than this, these amps are very well behaved, and new outputs and > >> fuses > >> will, in 99.9% of cases, effect a complete cure. Note, however, that they > >> have proper differential inputs, so are not that easy to drive correctly, > >> unless you have a proper balanced XLR source, and that they don't like > >> earthed test equipment connected to their outputs / inputs > >> simultaneously. I > >> usually hook a completely isolated speaker to them for final check, as > >> the > >> music shop which sends these to me for repair, often remove the amp > >> chassis > >> from the cab, to ease the transport, and save me having to strip it all > >> out. > >> He now tells customers when they collect the repaired unit, that they > >> should > >> brush out the air vents at three monthly intervals. > > > > I agree with Arfa, I`ve repaired dozens of these and always found the > > solderwork to be excellent. Perhaps someone else has been in there before > > you. There was a mod for early units, different output transistors and the > > addition of a couple of 1N7007 on the print side of the board. > > > > Ron(UK) > > > Well, I agree with Arfa and Ron. I've repaired lots too, since the cooling > is also IMHO inadequate, which is quickly made worse by fluff around the fan > vents. > Never had any dry joints, but seen plenty of the bulging caps Ron mentioned. > I replace them with 105 degree types regardless of apparent condition. > > One warning - it is easy to accidentally short the solder tags the big > diodes are soldered to, to the zero ohm links as you tighten the nuts. If > you power up fully in this condition with 4 amp fuses you will blow the > Darlingtons again. > You have probably noticed both speaker output tags have amplifiers on them, > there is no grounded speaker connection, though each output is referenced to > ground. > > > > Gareth. > I see no circuitwise reason for those repeated cap failures. The Darlington heatsinks are elevated off the pcb (trackside) with spacers and although the minor component side of the pa pcb is un-fanned I would not have thought pcb and working caps would get to 85 deg C Will make airflow mods and RTV-stick non-resettable thermochromic dots around various items , for if it bounces back. |