Vacuum Tube Preamp Repair, Harman Kardon Citation 1

hi everyone and welcome to another episode of mr. Carlson's lab today on the bench we have a harman kardon citation 1 vacuum tube preamplifier that's pretty well known in the audio circles what we're going to do is restore this thing and bring it back to its former glory yet again now just like every other piece of gear that ends up on my bench it usually has some form of a story to tell so what we're going to do is go through this thing and see how it's been treated through the years see what kind of repairs have been performed and we'll even analyze its design so let's see what this thing has to say for itself let's get started here's a close look at the face of this Harman Kardon citation 1 and what this is telling me so far is that either this unit has been living with an owner that's really taken good care of it or this thing has spent most of its time in a box I'd easily rate the condition of this externally about an 8 and a half or 9 out of 10 there are very few flaws it'll scratch down here I can see and you know some minor scuffs on the paint now this has just come straight out of the box I haven't done anything to this I haven't cleaned it up or anything and as you can see there is some surface dirt so really one of the things cleaned up it's only gonna get better so it's in very very nice condition if you're thinking of purchasing a preamplifier like this one of the things to keep your eyes open for is the lettering and the numbering on the face here for some reason I find that people love to drag their fingers on the face of these things and carve the lettering and the numbering off and that looks really ugly so if you buy a unit where that's happened be prepared to either you know re silkscreen this or find something that's aftermarket to replace it this again is in very nice condition people have actually grabbed these knobs like they're supposed to and they haven't been dragging their fingers on it on the bottom here we have a channel lay in a channel B so basically you can choose whatever channel you want to be right or left it has independent bass and treble controls for each channel we have a turnover control a roll control a blend and a low-cut here really interesting feature of this on the roll-off control is we have an L o n setting which stands for London so if you're going to be listening to records from Europe you'd want to put this on the London setting kind of neat over here we have a bunch of switches contour tape monitor stereo reverse and phasing control one of the things that always caught my eye about these preamplifiers is we have all of these knobs that are made out of aluminum but down here we have this weird kind of plastic almost not really see-through but kind of a diffused plastic knob whenever I see this I always think of an insert to one of these aluminum knobs it looks like an insert that would fit inside and there was supposed to be an aluminum knob on top of this but this is just the way they came so when you see this little plastic knob down here it's not actually missing a cover or anything that's just the way it is over here we have our volume control or loudness control and our mode setting function setting and a balance on the bottom so all in all it's a really complete preamp and it's got lots of different settings so you can really tailor the sound to the way you like it nice versatile preamplifier so what I'm gonna do is turn this thing around and we'll take a look at the backside here's a look at the rear side of this Harman Kardon ciation one and as you can see like a lot of modern pieces of audio gear there are lots and lots of input jacks here so these are all RCA jacks so everything is pretty much self-explanatory on the back here we have input channel a and B here and we have input channel a and B here so we have all of these different inputs for all of the different selections on the face of the unit here we have the outputs over here we have two outputs for channel B and two outputs for channel a so these would run off to the power amplifier and another neat feature is it also has a center channel amplifier output right here there a bunch of switched outlets here to run external audio amplifiers and whatever piece of audio gear you want to have maybe a record player or if you wanted to use a CD or a tape player you can plug these all in here and these outlets will be controlled by the switch on the face of the unit so when you turn that on these three here will get power this one here is unsalted tubes these things have they look like Telefunken yeah mater in West Germany Telefunken vacuum tubes right there so I'll remove all of the shields here in just a little bit and we'll take a look at all the vacuum tubes imagining they're probably all gonna be close to this the tube shields are in nice condition as well as you can see they're you know not rusted or anything like that so as you can see this thing is I say you know very very nice condition so whoever owned this thing has definitely done their job in keeping it in very good condition I notice on the top here that I can tell this lid has been removed at one time now that's most likely due to the reason that on the side there's a sticker here and it looks like it was serviced in 1964 so what I'm gonna do is turn the preamplifier again here and we'll take a look at those stickers as you can see on the side of the unit here they're a bunch of stickers this is dated 12 28 1964 so obviously this has seen some form of service it says authorized factory service here so it will be interesting to look under this cover and see what was done and see what a story this thing has to tell under there you can tell it's been opened because the screws have kind of marred the paint here and it's been shifted a little bit so the coverage has definitely been off and that's noticeable on the top side of the unit here as well so it'll be interesting to take a look inside this thing and that's what we're going to do next in order to get under the top cover here I need to remove two screws from this side and two screws from this side which I've already done now all I need to do is remove these four screws on the top and we should be able to get under this top cover so let's experience this together let's see what's hiding underneath this so yes I'm doing this very slow because I don't want to scratch the paint on this I'm guiding this with one hand and holding this with the other the fasteners that they've got on the bottom side as you can see are really chewing the screws up so chances are I'm going to replace all of these screws probably use some stainless ones or something like that maybe even use some small washers on here to cover up the Marne we'll see how that goes in the end you can tell it's really biting the screws just by dropping the screw you can see all the little metal flakes coming off just the fasteners that they're using on the bottom side there all these off of here all right what's underneath here we go wow that's actually looking pretty original doesn't even look like anybody's been in here before I'll just put the lid over here so what do we see lots of bumblebee capacitors that will all be electrically leaky so these will all need to be replaced these ceramic disc capacitors will be absolutely fine these can all be left alone no reason to replace these at all so this is brown black yellow which is 104 so that's point 1 micro farad with the yellow band meaning 400 volts so these will all get replaced all the electrolytic slick original so those will have to be replaced as well these are real troublemakers and anything of this age so those all have to go work on something to maybe keep the originality leave these in here and maybe put something underneath the chassis or something like that will come across that here in just a little bit so yeah looking really nice everything is so nice and clean in this thing very impressed not much tampering if any at all alright so this is only one side let's flip this thing over and take off the bottom cover and see what's on the bottom side maybe that will yield something different who knows in order to get into the bottom cover here just a bunch of screws that need removing this one this one this one here this one and this one and this one and the bottom comes right off and when I remove the bottom this thing looks incredibly clean inside it doesn't look like anybody's ever been in this thing so I wonder what that sticker on the side is of them over here bottom cover so again all of the original bumblebee capacitors here have to be removed there's a red marked Sprague here these are dye film capacitors and they usually don't leak but since I'm in here I'll replace it anyways if you ever see a Sprague capacitor with the yellow writing on them they're very bad for leakage they have to go again since I mean here I'll just replace everything or here's another little bumblebee this is point zero one micro farad so 103 and 400 volts that'll go you can see all the original diodes and fuse holders here and everything it just looks so incredibly clean again I don't think anybody's been in this thing I'm really wondering if this thing did spend its life in a box original line cord on it it's nice and soft there's no cracks to it you know nice and soft your no issues whatsoever very nice condition all the original capacitors aren't showing any physical leakage on the bottom whatsoever they're still sealed up nicely so again these will all have to be replaced somehow we'll go over that here in just a little bit figure out how we're gonna put some new capacitors in here so yeah all in all contacts are also clean and everything so this is a very nice example of a Harman Kardon ciation one so this is channel a on the bottom side here and on the upper side is channel B so what I'm gonna do is turn this thing back around and we're gonna start replacing these Bumblebee capacitors with a suitable replacement that should be dependable for a very long time I'm about to start the replacement procedure for all of these bumblebee style capacitors on channel B here I'm also going to replace this dye film capacitor right down here I'm going to talk a little bit more about the orientation of this dye film capacitor in just a little bit so when we get to replacing this I'll cover that then now I've made a few other observations about this pre amplifier and one of the things that I've noticed is in the assembly procedure of this preamp they used quite a combination of both carbon composition this is known as an Allen Bradley style resistor here and they're also using carbon film resistors now you might be thinking to yourself it looks like somewhere along the line somebody's been in here and you know done quite a bit of a replacement well if we look at the binding posts here all of the solder is the same color between the carbon composition and the carbon film resistors everywhere it doesn't look like anything has been resold 'red throughout time whatsoever even the flux that's on the binding posts to the carbon composition and to the carbon film resistors is all the same color throughout everywhere here so wherever I find a you know a carbon film resistor or a carbon composition resistor all the soldering is looking relatively the same so it's kind of an interesting thing to note about this particular preamplifier another thing to note is this preamplifier wouldn't have worked very well due to this resistor right down here I noticed that looking at this a little bit closer here what I'm going to do is I'm going to zoom in the camera on this little component here and I'll be right back here we are zoomed into the circuit quite a bit closer and if you look at this carbon composition resistor here it's broken so what can we learn about the failure point of this resistor through visual inspection well take a look at this end of the resistor first so we can see that the resistors body itself has got a nice crack in it and you can see that there's a nice light brown sharp edge where it's cracked there really is no evidence of any kind of burning or sparking at that end if we look at the lead in wire to the resistor itself you'll notice that there's a little bit of carbon at the end of the lead-in wire that's completely normal that's where the lead in wire is inserted into the carbon plug within the resistor body here you'll notice beyond the carbon there's a clean area right to the ridge up here that clean area is where this lead-in wire is see into the brown portion of the body and that little Ridge sits right at the resisters body edge you'll notice that the lead-in wire itself is on this angle here whereas the resistor body itself is on a different angle you'll notice that the lead-in wire itself is very short to a very fixed point I'm pushing on that you can see there's almost no flexing on this end here so this terminal type oint or terminal lug is very very solid whereas at the opposite end of the resistor this lead here is tied to a vacuum tube socket and what I'm going to do now is wiggle the vacuum tube what does all of this tell us well we know now that the resistor itself has broken through mechanical stress now whether this preamplifier went back way back when to an audio service place we saw that sticker on the top cover or whether this was a manufacturing default or whether this has happened through time we really don't know because there's a cover on this whole area here keeping the dust down there's very little dust in here and if we look at the resistor body itself it doesn't look like there's any dust on it at all now what I can tell through removing the vacuum tubes off the chassis so a wiggle a vacuum tube here again the tubes themselves are very tight within the tube sockets which tell me that there hasn't been a whole lot of tube replacement in this preamplifier and in a little bit here I'm going to go over that and I'll show you what I mean you can really tell how a preamplifier receiver or anything with vacuum tubes has been treated throughout time basically just by the condition of the tube socket itself and they have some stories about that as well so what I'm going to do to fix this problem is replace this resistor with another carbon composition resistor now the resistor that I'm going to replace that one with is a little better quality than what was in there you can see this red bander here that means that this has got a 2% tolerance or as this resistor here has a 10% tolerance due to the silver band whenever you're going in any piece of tube gear like this and repairing it you want to make sure that what you're replacing in the unit is better or equal to what came out now nowadays it's really kind of tough to know what you're buying when it comes to resistors and capacitors unless you buy from a very reputable source and you know that the resistors and capacitors are not counterfeit there are so many counterfeit resistors and capacitors on the market today it really is quite astonishing now a lot of people like to get into these things and replace all the resistors with metal film resistors because they think that they're quieter if you don't get your metal film resistors from a reputable source you may in fact be making your preamplifier quite a bit noisier so something to keep in mind I'm about to start replacing the bumblebee capacitors on channel B here and there really is a whole bunch of ways to remove these capacitors many of those ways really just depends on the tools you have and know how clean of a job that you really want to do now before I get started in actually taking these things out showing you my method here I'd like to talk a little bit about component leads stress and noise so any of you that have owned vacuum tube audio gear over the time and even some solid-state audio gear as well you've noticed that as the unit gets older sometimes they develop some hissing or crackling sometimes some random popping noises now a lot of these problems are contributed to component leads stress over time now when I'm talking about lead stress if you take a look at this capacitor in circuit here you can see that they've taken the lead and they've pulled it tight around this binding post number 42 here they've also done it on this side here well when you're putting the component in in your wrapping leads a lot of the times it actually pulls the binding posts together a little bit putting continual like a spring tension on the components lead so it's actually trying to pull the leads over time and much of the time that actually happens to resistors and capacitors it may not be quite noticeable but even just the slightest little bit of pull on those leads can cause a hissy staticky connection within the component now I've demonstrated this in some of my other videos I've located some hissing noisy components and again most of the time this is just caused by component lead stress now Tektronix way back in the day they did a whole bunch of things to alleviate these problems what they did on their larger oscilloscopes is they would install ceramic type oints and they would cut the leads of the component before they were actually dropped into the ceramic type oints so there was no mechanical lead stress and then they would solder them in so the component is basically just laying there and then they solder the the actual binding posts or the ceramic strips now that's very good practice to follow whenever you're designing or building anything or replacing components like we're going to do now so after I've removed these components what I'm going to do is cut the leads short and I'm just going to solder the leads directly to the side of the binding posts I'm not going to wrap them so there will be no mechanical lead stress on the component whatsoever and over time it won't be pulling on those leads now much of the time the reason that you see the reason that they've wrapped these things around these posts really isn't for mechanical rigidity or anything like that it's just because one person is putting these things in the circuit board or on this actual tie point board on an assembly line and then there's another guy that's actually doing thus altering down the line so whoever that person may be that's doing this all during down the line doesn't have to think all they have to do is this put solar on solder it and then it's off to the next person to test and that's the reason that they do this wrapping it's really basically for speed has nothing to do with mechanical rigidity that give me this thing is not in a high vibration atmosphere and it's you know way back in the day it wasn't flying around on a plane or you know being driven around in a car or anything like that right this just sits on a shelf so there is no real reason to put this mechanical lead stress on now if you were to replace all the resistors on this board I it would be a very time-consuming process because you're not going to be wrapping anything you would be installing one component laying it up against the actual binding posts themselves and then soldering them in and when I put the new components in I'll show you exactly how I do that the tool that I'm going to be using to remove these capacitors is a very sharp small clipper so I picked these up quite a while back and I'm very happy with them now you got to be careful with these things you really don't want to be cutting any large diameter wires or anything like that but for this type of work these things are great so this is an ear m77 6e now what I'm going to do is I'm going to use the binding post itself to work against to unwrap this lead so what I'm going to do is get this onto the post like this and I'm going to pull the lead away from the post and basically unwrap it so that's the nice thing about having a sharp clipper like this you can see that I'm already starting to pull this lead away and then basically what you do is you just twist it and it's almost kind of like you're basically peeling it off and look at that very easily comes off and I didn't even have to dassault or anything now on this end here I'm going to do the same thing now as I say your technique may vary you can see that how that works and it's very simple you're really not putting a whole lot of stress on anything here because you're just peeling the thing off you can see how easy that component just came out all the mumble B capacitors in channel B have been replaced and we'll take a look at that here in just a moment something very interesting to note about these Bumblebee capacitors when these were made they were very careful to mark the bands on this in the correct direction so where the rating starts 104 the brown band indicates the outside foil end in this capacitor and this is consistent with all of these capacitors and even these ones out of an old piece of Hewlett Packard gear so at the end that the rating starts is the outside foil now oddly enough on the channel B card every single one of these capacitors was backwards in circuit to the way it should have been installed aside from one we'll take a look at that here in a moment again so in order to demonstrate the outside foil and on this capacitor here the green LED will be lit with the lowest amount of signal on the oscilloscope indicates the outside foil and and I'll demonstrate that right now so I'll just click this in here and I'll put a little bit of noise into the circuit with my hand so you can see there's noise in it right now that LED indicates the outside foil end that's the lowest noise so when the LED is lit that end is applied to ground or to the common here on the case and the coax now if we look at this end that is the brown band the beginning of the rating do this in so you can see that's just me putting some noise onto the capacitor here coupling some 60 cycle hum into it really is what I'm doing with my body I'm acting as a hum antenna so you can see the minimal amount of noise is at this end and this is very consistent with every single one of these capacitors so I'll grab one of these out of another piece of hewlett packard gear and i'll put this in the opposite way so the brown band is now at this end so this LED should indicate now the lowest noise so on this to grab this a little too close to the leads at the end there try and make this viewable with the LEDs here so you can see Lois signal there Brown band here again marking the outside foil and now with all of these capacitors I've done the same thing I've taken time to mark the outside foil and you can see I put a little dot here right on the end so that marks the outside foil and these capacitors run down the line any old way so you can see that I have the writing both in the same direction yet one has a dot on this end this one here and the other one has a dot on this end here all right and to demonstrate this I'll just put this in a little test jig here try and get this out of the way and you can see this end is the outside foil end and if we look and see the little block dot there so that's marked and if we were to install this one the same way it should be the exact opposite because this end is the outside foil and here the way and there you can see it's nice and quiet on that end so again this is the outside foil end right here so when I've installed all of these capacitors in there I was very careful to note that and we'll talk about that here in just a moment let's take a quick look at Harman Kardon design and discuss what they did with those original Bumblebee capacitors so before I get started I've replaced all of the bumblebee capacitors with these capacitors right here all the way along this is a good name-brand Illinois capacitor and I know that these are going to be good for the long run now before I install these capacitors I made sure that I knew the outside foil end of each capacitor now every one of these capacitors along here has the outside foil and at this end of the circuit aside from this one capacitor right here and I'll talk about that here in just a moment now when Harman Kardon designed this they took the plate leads and made them the long runs so the plate lead is here you can see it runs all the way back to here and then this is the plate resistor here which is a 68 km resistor this is the correct way to design things so what you want to do is you want to keep the grid leads as short as possible and if a run has to be longer it should be at the lower impedance portion of the circuit and the plate of the vacuum tube is the lower impedance portion so that means that this end here is the outside foil end now as you can see all the way along here I've put a little dot on the inside of the capacitor here so you really can't see them in circuit but if you look here on the end you can see that little dot right there I do that to all of these capacitors now these capacitors run down the line any old way and they each have to be tested to indicate or to find which end is the outside foil end so as you can see I have two capacitors the writing is the same way here the outside foil end is on this end right here whereas on the opposite capacitor it's on and here now this one capacitor here is the only capacitor that's opposite of all the rest now in order to keep everything looking uniform I tested a whole bunch of capacitors and basically mark them so what I did is I took one of these capacitors like this with the outside foil on this end and installed it this way whereas all the rest of them the outside foil end is here just to make things look uniform all the way across yet again the dot is on this side of this capacitor whereas on all the other capacitors the dots are all on this side here what I'm going to do is print out a capacitor map for this particular preamplifier and I'm going to put it into an attachment and I'll put a link just below this video here and I'll mark that so if you're interested in having the capacitor map for this if you want to make sure that your capacitors are all installed the correct way just go to that link and it'll be a you know a free download there so you'll see that I haven't changed this dye film capacitor here yet and that's because I wanted to talk about that this end here is the ground end so you can see there's a whole bunch of grounds attached to this end here and then this and runs off as you can see on this dye film capacitor there's a red band here the red band is the outside foil and again the outside foil end always goes to the lower impedance portion of the circuit and that is tied to the ground and so this is installed correctly now why they installed all of these capacitors this way in the circuit is beyond me they should have actually been installed this way all the way along this one here would have been the opposite way and then all the way along again these would have all been like this if they were installed correctly now I've looked at pictures of other amplifiers just to refresh my memory here and many of them are installed the correct way it's just this one here seems to have them all installed this way and it's the same on the other side as well so very interesting very very interesting at any rate that's all corrected and these things are now orientated in circuit the correct way and I'm going to do that on the opposite side as well once I change this dye foam capacitor out changing the capacitors on the bottom side is a little more difficult than the caps on the upper side just because there's a few obstructions in the way there's two pipes here that are carrying wires and there's this little choke that needs to be moved out of the way there's a bumblebee hiding on the underside here tip this forward you can see the bumblebee right there so in order to remove this is pretty simple just remove the nuts and the bolts here and move this out of the way and you really don't need to take any of these nuts and bolts off you can just move this around as you're desoldering the capacitors here so not too big of a deal these are pretty flexible this is sunk down into the chassis here just a little bit you can see that you see the tube sockets here no this is kind of sunk down so again a little bit more difficult not a big deal and again all the capacitors are the wrong way in here the brown band should be at this end here again aside from this capacitor here so that'll all get corrected and also replace this dye film capacitor here and we'll move on to the electrolytic s-- all the Bumblebee capacitors have been replaced on channel a as well as that dye film capacitor and now it's time to focus on the electrolytic capacitors here on this chassis now for aesthetic reasons I'm going to leave the original capacitors in because they're in very nice condition and there is no signs of any physical leakage on the bottom here again this thing looks like it really has low time on it so what I'm going to is install the new capacitors on the bottom side of this little chassis here and what I'm going to do is remove the wires from the original capacitors here and install some ceramic standoffs and fasten the new capacitors to the ceramic standoffs and want to have them all installed I'll show you exactly how I've done that now whenever you're replacing an electrolytic capacitor you cannot leave the old one in circuit just because common failure point of these capacitors is a short or close now of course if this capacitor shorts encloses one of the original ones and you have the new one tied to it really the new one really doesn't mean anything because you know this thing just turns into a jumper to ground so you want to make sure that you always remove the old capacitors from the circuit you can never leave old ones in and then you know basically just parallel new ones doesn't work now this particular capacitor here has only one capacitor inside the can you can see that they could have put three capacitors in here but there's only one pin really populated on the bottom of the can here so there's one cap in this can there's one cap in this can here there's two capacitors in this can with a common ground and in this can here there's three capacitors with a common ground here on the side of the can is a legend you can see that there's a triangle there's a kind of a square rectangle here and then there's a Halfmoon over here if you look on the side of the can there's a legend and it tells you what each capacitor does on the side of the can so if it says say 40 micro farad at 450 volts and then there's a little triangle beside it that means that that triangle is that particular capacitor and so on all the way around and a lot of the time you'll see on the Canon says can com- so that means that the can is negative now in some cases the actual can is isolated from the capacitors and will be a ground or a common on the bottom of the can but it'll usually tell you that on the side of the capacitor as well so that's why you see these little squares you see a little square here over here you know again rectangle here and then a triangle and then a Halfmoon and you can see they've got them marked here as well it's just that they're not populated and this is same down here so I was to move the pins you'd see the other legends as well so that's what they do with these older can style capacitors now these capacitors are usually well eighty eighty-five degrees something like that the new capacitors I'm putting in are 105 degrees C and they have an extremely long hour rating at that so they're very robust capacitors and another nice thing about install on the bottom with standoffs is in the future if they ever need to be replaced these are modern capacitors and you can just get under here and replace them very very easily a lot of people like to restock the cans so what they do is they cut the old capacitor open on the top and then they put the new capacitors in the can and then reseal the can again well that's all fine and dandy but one day down the road their electrolytic capacitors and they're gonna probably need to be replaced again so why not just make it easy for the next replacement and keep everything nice and clean looking so what I'm going to do is start getting going on the installation of the capacitors on the bottom side here and gonna have everything installed I'll come back and I'll show you exactly how I've done that all the new capacitors have been installed into circuit and they're soldered to the ceramic standoffs all the old capacitors are disconnected from circuit and they're basically just acting as supports for the new capacitors in a moment I'll zoom on into this and we'll take a closer look at what I've done I still need to replace this Bumblebee capacitor here this is across these diodes this is point zero one micro farad at 400 volts and I'm also going to replace the ceramic capacitor that's across the line cord I'm going to replace this with a modern safety capacitor this is very very important to do whenever you're working on an older piece of equipment like this these older capacitors aren't designed to open when they fail a lot of them closed the newer safety capacitors open so that makes things quite a bit safer so this is an absolute must you need to get rid of these older ceramic capacitors that are across the line cord the older the piece of equipment the scarier the capacitors are a lot of the older vacuum tube radios older vacuum tube amplifiers and even older test gear have paper capacitors across the line cord and from the line to the chassis this makes an incredible shock hazard present so that definitely has to be addressed I'm going to do an entire video dedicated to safety capacitors and installing them in older equipment here in the very near future so something to definitely keep in mind notice that on a piece of older equipment like this it has a line cord but it is not polarized so this line cord here can be plugged into the wall this way or it can be plugged into the wall this way now in a lot of older equipment there is a capacitor across the line and from the line to the chassis so depending on which way it's plugged in if one of those capacitors say it's a paper capacitor is shorted to the chassis the chassis of your unit is live very very dangerous so again in the near future I'm going to do an entire dedicated video about safety capacitors so what I'm going to do here is zoom on in and show you what I've done with all of these electrolytic capacitors here so you can see I've soldered in the ceramic standoffs to the old capacitor pins here and there even soldered in the center so this is incredibly sturdy the little standoffs are on an angle like this to keep the connections away from the chassis if I tip the chassis here a little bit you'll be able to see that you can see how they're angled and it's like that with all of them they're all on an angle they're sticking up like this this one here as well and this one here is mounted straight up and down so the old capacitors are just acting as supports now for little ceramic standoffs and all the new capacitors are soldered to the ends so it makes a nice clean modification you just basically take the wires from here put them to here and then solder in your new capacitor this makes for a very easy replacement in the future you can see how easy these would be to replace it just clip a bunch of wires take it out and put a brand new capacitor and now these are very high quality capacitors and I doubt that these things are going to need to be replaced for a very very long time but still it's always nice to think ahead and you know prepare for the future the point zero 1 micro farad bumblebee capacitor across these diodes has been replaced and I've also replaced that ceramic capacitor across the line cord with these to safety capacity now the factory capacitor is actually 2.0 1 micro farad capacitors in one case now it says here 2x point zero one that's not to be confused with an x2 rated capacitor all this means is that there's two point 0 1 micro farad capacitors in this case now those 2 point 0 1 micro farad capacitors are in series and all I have two other capacitors here I'll show you what I mean here in just a moment these capacitors rarely fail but they need to be taken out of the line cord application so these need to be removed because this is not a safety cap so what I'm trying to tell you is you don't need to throw this part away if it's still working you can throw this thing in your junk bin and you can use this in a non safety related application so this capacitor here if we were to look at to safety capacitors and we were to just basically solder the two Center pins together so I was just to take these and solder those two pins right there together like this this is basically what this is like this that's all so just two ceramic capacitors in this block basically in series and that is how this is hooked up here one leadest here we have both of the capacitor solder together here which would be the centre lead of this capacitor and on this end here is the other end that's basically what's going on so now that that's done what I need to do is get behind the face here and replace the dial lamp that'll be the next step that's a pretty simple step all that needs to really be done is you have to remove this screw here this screw here and then if you flip the chassis over there's another two screws and just pull off all the knobs there on splined shafts take all the knobs off and the face will just come off and we'll replace that dial lamp once you've removed the four screws from behind the faceplate so there's a screw here a screw here and then there's one on the bottom here and one on the bottom here all you have to do is remove the knobs they're all on spline shafts so they should come off relatively easy now when you replace the knobs and put the knobs back on there really is no indexing so what you want to do is either turn the shaft over to one side and then line the pointer up to you know one of the markings there's a bunch of different ways of doing this if there is a center mark a lot of the times what you want to do is align it to the center mark and then it should follow when you move it either way there's a bunch of different ways of doing that but still relatively easy now throughout time I've come across all sorts of different situations I've had people glue knobs on and that's absolutely horrible there's no reason to do that if these knobs are loose you can take a screwdriver and very carefully slowly bend them if you try and put too much force on them a lot of times you'll break one of these right off so you have to do this very very carefully and even more carefully with the aluminum shafts so again you can stick a screwdriver in there very carefully part them again they break very easy so be very careful what you're doing just go up this very slow if you're gonna try and part these there's another way of securing a loose knob on a shaft if you're worried about you know it being too incredibly loose you can take a little bit of just any kind of cellulose tape cut a small strip and then just put a small strip over this and then put the knob back on and a lot of the times the cellulose tape will give enough area or you know take up the slack so that it gets pretty tight after that point so the bunch of different ways of going after this definitely don't ever try to glue or even use any kind of a hot glue or anything to hold the knobs on to the shaft because the next time you have to get in here to change that dial light you'll be teaching yourself a couple of new words I'm sure so once those screws are all removed and all the knobs are off this just very simply comes off like this and this is a very good excuse to get in here and clean the face of this now when you're cleaning the face of this you always want to work on an inconspicuous area first and you want to use a very mild detergent if you're unsure of what you're doing or what you're using don't clean the face because there's not worse than taking the lettering off so again very mild detergent and always test it in an inconspicuous area so the dial light lights up are very out of place looking knob here I'll just zoom on into this so behind this little washer here this is just a stop it from shining through the face and shining into the knob there's a little bulb in this holder here so all you need to do is just remove this screw right here this whole thing will come out and you can replace the dial up in the style ample again illuminate this somewhat out of place looking knob once you've replaced the dial lamp which is an 1815 or number one eight one five you're going to want to check to make sure that it works before you put the face in all the knobs back on there's nothing worse than putting something all back together and finding out that you've installed a dud for a dial amp and it does happen I've come across my fair share of them if you put your entire unit back together and you found out that the bulb is still not glowing there's another thing you need to check before you take the whole thing back apart again the dial amp itself in this unit is in series with the filaments of v5 or vacuum tube number five so if the filaments in that tube are open the dial lamp will not glow they are in series so one thing to keep in mind another thing before you go putting the face back on you're going to check to make sure that all of these nuts on the shafts are tight over time they do back off and get a little bit slack so sometimes you'll find that you get a loose control and maybe a wafer switch or a potentiometer mic rock back and forth when you're moving a knob so another thing is just tighten these up once you've cleaned everything in here on the face inside here another thing that you're gonna want to do just before you put the face back on its put a drop of light oil right on the shaft where it enters into the potentiometer and that'll keep everything nice and lubricated and moving smooth for a long period of time now you don't want to saturate anything with oil basically you just want to put a drop right where the shaft or where the little retainer ring is where it enters the potentiometer or wafer switch and oil will leech into the shaft area here where it's inside and it'll keep things moving smoothly so that they don't seize up or get rough after that you're pretty much ready to put the face back on again one of the ways to tell how much time there is on a vacuum tube device or to get an idea of how it's been treated throughout time is to remove a vacuum tube and basically feel how tight the tube is within its socket so I'll give you an example here all the tubes on this chassis are very tight gently rock this tube as I'm removing it you can see it doesn't really want to let go of that vacuum tube very well that's a nice tight tube socket and all these little contacts in here haven't been stretched apart now if you find that when you're pulling the vacuum tube out it basically falls out chances are you can want to replace that socket or at least try and pinch these little contacts back together again if you have a small jeweler's screwdriver a lot of the time you can stick the jeweler's screwdriver between the actual socket itself and the contact and push them back together so again you know the better option would be to replace the actual tube socket so that it makes proper contact to the pins now another thing that a lot of people don't know is that some of the newer import vacuum tubes I guess you could say have smaller pin diameters than the older vacuum tubes so if a device has had an older vacuum tube in it and you put a say a newer one of these import vacuum tubes in there a lot of the times they're just loose because again the pin diameter is smaller so that's another thing to keep in mind now that's not necessarily a bad thing I find that a lot of the newer vacuum tubes with these smaller pins the pins are almost polished and you know they make very good contact when they are in the socket again they're just a smaller diameter so they will seem loose when really the socket is probably okay at this point we're just about ready to try out this preamplifier and see how it works one of the things that I want to do just before I do that though is clean all the potentiometers and the wafer switches with a very good quality contact cleaner this is very important if you don't do this all the dust that settled into these little controls over time will make staticky connections you know and even in the actual wafer switches you know sometimes you get an intermittent connection so what you want to do is take your preferred contact cleaner of choice you want to make sure that it's a pretty high quality contact cleaner and that it's suitable for being sprayed inside of potentiometers and on open contacts on wafer switches you want to take that you know and spray a liberal amount on it and then just work the controls on the face of the unit so basically you're just moving the contacts in and out a bunch of times and give them another spray and usually after that you know pretty much soak up the rest of the residue and you're ready to go at that point so that's what I'm going to do next and that'll take a little bit of time because there's a lot of controls and I have to work each control and make sure that I get the contact cleaner into all the contacts the restoration procedure for this Harman Kardon citation one is pretty much complete at this point there's just a few minor things I need to do before I put the covers back on one of those things that I'm going to do is replace these pieces of tape that are coming off the wires here they're just using tape to loom the wires together you see right here and right up here so I'll replace those with some modern zap straps now this is something that you want to do right in the end of the restoration or repair I know a lot of people they want to you know keep everything clean as they're going along and you know keep the wires nice and you know tightened loomed but the thing is is that in the end if you're testing something and there's a wiring error or say you know you need to trace a signal or something by separating the wires you're just gonna end up clipping up all of your brand-new zap straps so again something that's just done right in the very end now the testing procedure for a preamplifier like this is extremely time-consuming and this thing has been running on the bench for probably four hours now the things that I'm looking for is noisy staticky resistors and noisy staticky tubes and noisy controls and things like that so this has gone through a complete test at this point of both channels and what I'm gonna do is just shorten this up and give you an idea of what I'm doing here so I have a four hundred cycle signal running to one of the inputs right now and that's that yellow alligator clip that you see back there the white alligator clip goes to the signal tracer and the signal tracer is just acting as an audio power amplifier that's really all the signal tracer is audio power amp with a very sensitive front end I did a restoration on this Heathkit Model T 3 signal tracer in an earlier video and there was actually some some design errors and this thing that I corrected as well that's in that video so a very handy signal tracer to have around especially when you're testing preamplifiers like this an oscilloscope is a must as well and I'll cover that here in just a moment so I have that hooked up to one of the outputs so just one channel right now and if I advance the loudness control or the volume control you'll hear that tone that's coming out of the speaker on the signal tracer right now [Music] now that's a 400 cycle tone or very close to you can use a thousand cycle tone or whatever you're comfortable with to test this now another test that's very important to do with an oscilloscope is you want to check the amplitude of both channels with the balance control centered you want to make sure that the amplitude is very close to being the same with the balance control centered it's a little off to one side just to touch off to one side not too big of a deal but if you find that the balance control is way over here to get the amplitude the same on both channel and channel B chances are there's a faulty resistor in the circuit somewhere or you have a bad vacuum tube so what you're doing is you're bridging both channel a and B inputs together and you're looking at the outputs separately on a dual-trace oscilloscopes and in future videos I'll go through this and more detail again a very time-consuming process one of the things that catch people when you're working on preamplifiers is the really sensitive gain stages so we have a 401 402 and tape HD here and they're all extremely sensitive now you can't test these stages with the bottom open like this you can see how I've got the yellow and the white alligator clip in there you need to have all the covers on the amplifier and you need to test the preamplifier like it would be operating in normal service with the covers removed it's very susceptible to hum and it could lead you astray to thinking that you have a problem with a vacuum tube or something like that when really the reason it's humming is just because the covers are missing so something to keep in mind so all the controls have been tested on this again just hours of operating and moving things around the step controls here have been tested and everything you know all the switches have been moved around everything is nice and silent after the contact cleaner it's running nice and cool there's no issues whatsoever everything is working perfect the sine waves are really nice and clean on the Scylla scope and the amplitude is very close so all in all I'm very happy with the outcome of this preamplifier it's working extremely well thanks for stopping by the lab today I hope you enjoyed this video if you did you can let me know by giving me a big thumbs up and hang around there'll be more videos coming like this in the near future so if you haven't hit the subscribe button you might want to do that as well if you're interested in taking your electronics knowledge to the next level I have an ongoing electronics course on patreon right now this is dealing with solid state and vacuum tube electronics alike I'll have the link just below this video right about here in the description so if you click on the link it'll take you right there and you can check it out while you're there you might want to check out the community section as well there's lots of people there sharing their projects so until next time take care bye for now you

Channel: Mr Carlson's Lab

Views: 243,589

Rating: 4.9449496 out of 5

Keywords: Harman Kardon amplifier, Harman Kardon preamplifier, citation 1 repair, Vacuum tube audio, audiophile, audio amplifier restoration, audio amplifier repair

Id: E_5cVxeoG7U

Length: 56min 44sec (3404 seconds)

Published: Sat Sep 16 2017

Reddit Comments

[u/veni_vidi_vale]

I find this video strangely soothing. Like ASMR for audiophiles :-)