Tools For The Bench- High Voltage Power Supply Repair!

hi there and welcome to another episode mr. Carlson's lab I recently purchased another tool for the bench recall in the op-amp video I needed another regulated high voltage power supply so I managed to find one at a pretty decent price it's far from pretty looking but it'll definitely do the job so what we're going to do is go through this power supply repair it bring it back to life and I'll also explain how this power supply works so let's get started this is the power supply that we're going to be taking a look at today and as you can see it looks like it's had its fair share of use it's got a crack in the meter face here so there's just a plastic cover not too big of a deal it's got some scuffs and scrapes and the binding post for the heater supply is bent down now that could have been done on purpose the common is in the center here maybe somebody did that again you know this has been through many hands at this point I'm sure so who really knows what people were thinking at the time now I really don't know what's going on inside this thing the story on this thing is is the fellow who did illness at one time liked to experiment with vacuum tube amplifiers and it looks like it may have some modifications from the outside and I'll show you what I mean here in just a moment so who knows what's happening on the inside we'll discover that together so this is a regulated high-voltage power supply so it'll source about a hundred milliamps a little bit over for intermittent periods of time at about 400 volts or somewhere in between on the C supply it which is the abayas supply it'll go from zero to negative 100 volts at one milliamp you don't really need much current there because that's just for biasing tubes and things like that it has a heater supply 6.3 volts AC at 4 amps so you could run quite a string of vacuum tubes off of that alone and off standby and on switch here so if you're not going to be using this from long periods of time you can click then into standby and with regulated power supplies that really is quite handy to have now over here you'll see this lambda power supply that's the one that I normally use so this will be a secondary supply and I may even use this in lab number two occasionally you know to work on radios or amplifiers or test or whatever it really is just a universal power supply and you know they're really handy to have around as you saw with the video that dealt with the op-amp I had to put a small power supply together to get that other supply so this would have done that so when I say this thing looks like has been modified if we look at the back side look at that a big washer and a screw in another washer and somebody's put this cord in here so not a very nice-looking modification I can tell you that so I don't know if the original line cord was intended to go there or not there's a little punch there so this looks like it's been I don't know it's a pretty ugly looking mod so be interesting to know what's been done on the inside hopefully it's most of its there at any rate so what I'm gonna do is I'll flip this thing up and I'll take the case off it's really easy to get the case off on these older pieces of you know test gear this old Heathkit all you have to do is just remove these two screws which are not original screws as well you can see there Phillips screws here so those two screws and the back should just come right off and we can see what surprises hide inside okay let's take a look inside this thing and see what we find this is always the fun part I really enjoy this not done my best not to look through any of the holes around the slots on the bottom so that we can experience this together these things always tell some form of a story and as you can tell it's yelling that story pretty loudly with with this thing right here so who knows really what's gonna happen find some RadioShack transformer hanging off the side of something who knows right this is always the fun part all right screws there here we go came off nice and easy Wow 6l sixes look like there I would say new they say de strim on them but they're very clean all right let's take a look at the top side of the chassis first I just saw the bottom side so kind of have an idea what's going on there already so what I can tell so far the story that this thing yells is that somebody wanted to use this thing in a hurry so they didn't clean the the chassis at all what they did is they wipe the dust off and they took a felt pen and mark the tube numbers on there you can see that it's just basically finger wipe and then the tube numbers now these look like they're a little bit dirty but these look very clean now the guy that sold me this power supply is an audio guy and these are audio tubes so probably what happened is maybe he wasn't expecting to sell this thing so I went you or I called him on the phone and went over there and he's probably thinking oh I pulled the 6l sixes out of that I'm gonna put them back in that's probably what happened that's why they're so clean like look at them they're spotless wipe down with Windex aside from a little bit of surface dust right this one here is pretty clean as well so kind of interesting now this looks like it could be original writing because that's under a thick layer of dirt there but who really knows so on the top side here we have 2 0 a 2 tubes which are 150 volt regulators so you can picture these things as 2 150 volt Zener diodes so 150 and 150 so these are obviously going to be a reference either one or both of these are going to be a reference I don't have the schematic yet I'm sure I'll find one the stuff for this Heathkit equipment is usually really readily available sometimes not but you know I'm pretty sure this is a pretty common kind of power supply 6 ph 6 it's only purpose would be some form of a control tube before these 2 6l sixes and the 6l sixes would be acting as the passed tube so these things are acting like very large variable resistors and this 6b h6 is telling these two tubes what to do and these 2 0 a 2 tubes either one or both is acting as a reference for this tube this is a 6 X 4 so this is a rectifier of some sort so it's going to be changing AC to DC for some supply in here and we'll find that when we look at the schematic so the topology of these linear type power supplies is you know pretty close now you could very easily compare this to say like an astronomically just looking at its purpose I'll explain what I mean here so in an astronaut RS 50 power supply you know how you got those big transistors on the on the side so big linear power supply inside the extreme power supply is an IC that is known as an LM 7:23 and that controls those pass transistors through a driver transistor so that IC is basically telling those transistors on the side of the unit to supply more current if it's needed and that's basically what this six bh6 tube is doing now there's a driver transistor inside of a Strom power supplies because they are transistors and they're current driven devices right so vacuum tubes are very much like FETs their voltage driven devices so this very small tube here can control these tubes with ease in fact it could control a whole lot more than just these two tubes and i'll get into that here in just a little bit when we look at the schematic so basically how this power supply is working okay say we want to draw say 300 volts from the face we need 300 volts off the banana jacks on the front of this unit so we hook that 300 volts to an amplifier that amplifier is going to draw current so what's going to happen is it's going to want to pull that voltage down so what happens is is this six bh6 tube in the blink of an eye tells these two tubes here to supply more current to make sure that voltage stays at exactly 300 volts so these are like two very large variable resistors kind of like a volume control so once you draw a load this six bh6 instantly says okay we need more current turn it up and then when you remove that load instantly back things back down again and that's what's happening in this it's it's pretty simple what I'll do when I get the schematic is I'll go through this and in fact you know what I'll set up a display with a very large variable resistor and show you exactly what happening when we draw current and what this tube is doing so that should be kind of a fun display so let's take a look at the bottom side of this thing yikes solder here to hold this thing up okay maybe two rows of cylinder design there we go nice and steady okay so what I see so far is he's been in here somebody's been in here and recapped this thing the highest quality cap in here would be this thing right here all these other caps look like no-name brands this one looks like it might be actually leaking some form of a fluid maybe the vents stamp on the top is leaking who makes these caps cheong it says on the bottom so those are out of there this is who makes these things gee luxe on those are out of there and these are made by JW CEO who knows those are gone as well I can see the diodes have been replaced so obviously the original diodes have gone chances are the original diodes went because somebody did not replace the capacitors and powered this thing up and it shorted the diodes there are two failure points for these diodes that will cause the diodes and a power supply to fail and I'll explain that here in just a little bit this is something that really isn't talked about a whole lot you really can't find this information around it's really specific stuff so what I'm going to do is I'm going to do my best to explain what kills diodes and power supplies especially power supplies like this so the line cord is looking kind of scary yeah you used a color-matched eat drink fancy that's running there up to the top side of the chassis the black lead is here almost no strain relief you can see that's banjo string tight not good this was originally issued with a 2 wire chord it will get a 2 wire chord again now if you're comfortable with having a three wire chord and grounding the chassis out in a power supply where you can reverse the polarity of the face at any time that is up to you you need to keep in mind that if you do put a three-wire cord on something like this if you plug this into the wall immediately the chassis it's okay we'll look at it like this so say you have a guitar amplifier here three wire plug just like this one so alright three wire plug like this one and you have this thing plugged in three wire plug like this one and you plug them both in to the wall immediately there's already a connection between this and the chassis of the amplifier so the chassis ZAR connected as soon as you plug these both in with three wire plugs now since you can actually reverse the supplies on this and things like that that could pose issues in some situations and you know as they say it's personal preference if you can remember on this power supply here on the face they have an actual chassis this is ground here and common we can see and you can see here it shows that you run a bridge bar between these two and I would not doubt in the instructions that it's going to tell you to join those so basically what you're doing is you're taking the negative of this and you're attaching this to the chassis well if you put a three wire plug on this thing the chassis of this thing is no longer isolated from the line because in your breaker panel in many situations the safety ground put these rules of solder back under here and Center this the safety ground is a tie is tied to the neutral in the breaker panel so that means that this line in the breaker panel makes a connection to this line right here in this line is directly connected to the pole so it's not really isolating the chassis now safety grounds are for safety that's what they're here for and in many cases you know safety grounds are extremely important to have and again if you feel comfortable with a safety ground on this if it makes you feel safer and you feel that that's a safer thing to do definitely put on the safety grown personal preference for my own purpose I'm going to reinstall that 2 wire cord so this was issued with a 2 wire cord as well again for my own purposes I want the chassis isolated now let's see what else can I tell you here oh yeah this thing is loaded with high voltage this high voltage all over this place scary amounts of high voltage so these caps are rated at 400 volts and from what I can see here this looks like this is in some form of a doubler configuration so it's gonna have a lot of voltage in here what they're doubling so this thing has to supply 400 volts so it's probably five 50-plus volts in this power supply I'm thinking so again we'll look at the schematic here in just a little bit so that's a lot of voltage to have in a chassis like this so if you don't know what you're doing you don't want to probe around in this thing and if you powered the thing up and it has caps in it there's a really good chance that those capacitors are going to hold a charge for a very very long time so you need to be extremely careful in a chassis like this these capacitors can hold a deadly charge for weeks a month depending if resistors are open and the capacitors are very good they'll hold a charge in fact I have this capacitor here this is a really good capacitor this Illinois cap right here I've got a whole bag of these things that are brand new and this particular capacitor here I had charged up and it was sitting on my bench for over a month and it was charged up and I grabbed it and I threw it so you know the the whole charge for a very very long time so you got to be extremely careful in this so what else oh look at this so this is running to a fuse here so this is a hot lead right runs to a fuse goes out the fuse here through this which is looking like a piece of speaker wire it's just tied together here and it runs back out and goes over the transformer so what I can see is this originally was this one wire here and for some reason somebody cut it and put a piece of speaker wire and twisted it together maybe a remote on and I don't know scary stuff so anyways that's got to go and all the caps have got to go you know these are probably okay so these look like a mormon in style if a pastor here but you know legally assist flying leads hang in the middle of nowhere um what else just you know the standard scary stuff that you find when you open up a chassis believe it or not this is actually looking pretty good yet to most of you that are dealing with circuit boards all the time this probably looks like a rat's nest when it kinda is it's not all that incredibly bad so compared to some of the stuff I've seen Wow the person that soldered in these diodes did an okay job and they're one in fifty four oh six looks like you know fifty four oh six is they're all 54 so 600 volt diodes so chances are it's kind of borderline yeah I'd probably be okay yeah that's about it it's it's not looking too bad not looking too bad at all so it's a you know it's a nice foundation let's look at it that way at least you know there's I didn't find a rat's nest inside this thing a literal rat's nest or anything like that some of the things that I've opened up they've the chassis itself hasn't been in the case for long periods of time and they've been sitting in a puddle it looks like and and I think this this looks yeah it feels like a metal chassis see here yeah it's it's a metal chassis alright so yeah it's in good condition there's no rust on it the plating is all still on it not too bad the face would be aluminum that's really soft so what I'll do is I'll find a schematic I'll go over the schematic with you guys and that'll set a demonstration up with a big variable resistor and I'll show you exactly what these tubes do and how it affects that and that should be an interesting little demo I managed to find a really nice schematic so let's get an idea of what the engineers that Heathkit were thinking when they designed this power supply and I can see there's a whole bunch of things kind of going on in their head already a little bit of cost-cutting here and there and using up components that probably have been kicking around for a while now I'm gonna talk about some things that aren't normally talked about in these types of power supplies so if you're interested in servicing high-voltage power supplies with tubes like this you might want to get out a pen and a piece of paper and take a few notes again not really commonly talked about stuff here so first of all we'll start with what looks to be the negative supply so we have a 6x4 rectifier here and you can see both of the cathodes are attached to the plate of this regulator tube it runs through a bridge in the regulator tube and then just ties to common here so this rectifier tube is attached in a full-wave configuration but what they've done in order to make this a negative supplies of course this is isolated by its own winding and they're taking the positive and they're putting it too common here now these two 0a tubes are hooked up in series so this is acting as a shunt style regulator setup and you can see the center tap of the transformer which would be normally the ground is running out and they're using that as the negative supply so it's write negative 380 or 390 volts here goes through two resistors here and of course because these are 150 volts each we get regulated negative 300 volts here and they're using that all over this you can see between these two tubes they're using that as the reference for this six bh6 tube which is the control tube for these two 6l6 pass tubes and I'll talk about how this works in a little bit it's a pretty tricky circuit to troubleshoot if you don't bridge these tubes out and put a load here because the circuit is always correcting so if you're going to be putting a load across here of course these tubes are going to supply more current and this circuit is continually correcting itself so the best way to troubleshoot something like this is to get rid of the past tubes put a fixed resistor across here and put a fixed resistor across the load and you can actually see how this six bh6 tube is working so I'll simplify this here for you and in basically what I'm going to do is insert an error here so what I'm doing effectively is I'm taking out these six l6 tubes and I'm putting a resistor across here and a resistor across here when I'm explaining this so we can see how this works because this is continually correcting and if you were to try and see what I'm saying with all the tubes in circuit it would be really hard to see so let's start with putting a load across the terminal again so we have a low and say we're supplying 300 volts okay so there's 300 volts and we've got a load across here or we're going to put a load across the output here so the volt meter is gonna say 300 and we'll say we want to pull you know the load here is going to cause us to draw 50 milliamps or something like that okay so right now the current meters down because there is no load so we have 300 volts on this line right now so now I put a load across this this instantly jumps up to 50 milliamps well what's happening here is when I put that load across here the voltage at this point drops down because we're pulling current if that voltage drops down you can see we have a negative supply coming up this way to the grid of this tube this grid controls this tube if we draw current at this point the voltage is going to drop down causing the negative voltage here to go up the more negative voltage we put on the control grid of the tube the more this tube shuts off when this tube shuts off it's not trying to connect you can look at it like this when the tube is on it's trying to connect the plate to the cathode when the tube is being turned off it's reducing that connection so it's becoming more resistive between the the cathode and the plate here so again if you put out a really strong positive voltage on the grid you could look at it like it's trying to join the plate to the cathode okay so since this is shutting off what's gonna happen here is this is not gonna pull down and it's gonna allow the voltage at this point to go high if the voltage goes high it's gonna turn on these tubes and it's going to allow these tubes to pass more current and correct that situation and I will explain this here shortly with a VR and I'll show you how this tube is acting like it's got its hand on the center of a VR and it's turning a voltage of a variable resistor up and down to correct the voltage drop at this point here by supplying more current it really is a neat setup and again this is in somewhat of a loop so very hard to troubleshoot without bridging these out with just a fixed and then putting a fixed resistor across here and saying have this read 250 or 300 volts and then it drawing 50 mils and then you can add different loads across this to see how the tube reacts now this is the high voltage side here this is the high voltage side that's supplying 600 volts so it's above 550 600 volts to the plates of these tubes there has to be this here because when you draw current it's gonna pull that down and we need regulation to happen right we need a steady 400 volts at this point so that's the reason they have a lot more voltage up here because when you start to draw current it's going to pull that down and this is going to be acting as regulation at this point right here as you can see at this point here we have a voltage divider between this point which is completely unregulated right here going through a 1 Meg resistor and through 150 K on resistor to our reference so we have this at this point here acting as a sensing point and we have this side here which is also correcting if you take this 1 Meg resistor that's applied to the screen grid of this tube and say take that 1 Meg resistor down to will say just for argument's sake 100 K ohms okay you can actually make this overcompensate by making this more sensitive so what would happen say is there's 300 volts right here and we apply a load that makes it draw 50 milliamps so it's 300 volts we put the load on and this will go up to say 305 volts now so it'll overcompensate it'll actually give you more and then when you remove the load it'll drop back down to 300 again all by just changing this resistor here so if you're designing a power supply like that you want overcompensation this is the area to get that so you would want to correct this value right here you can really fine-tune this value to make this really spot-on right so you have lots of sag happening here you got to remember that if you're gonna pull load here it's you know gonna pull up the voltage down at this point so what's gonna happen is this is gonna have to supply more current if this supplies more current is putting load on this transformer so it's pulling down the other supplies as well a little bit because you know what's you know loading the transformer so there's a lot of move in a circuit like this and all of that has to be corrected for and that's why we have this on this side here and we have correction on this side right here this is a really interesting closed circuit another thing that really is uncommon about this Heathkit regulated power supply is that they're running these 6l sixes in a pentode style configuration usually in pass service what they do is they try they tie the screen grits to the plate and they use them as triodes by having a separate power supply here and running these in a pentode style configuration you get more sensitivity basically what they're doing is they're making it sensitive to run with the six bh6 tube very neat setup it's it's odd most you know linear type power supplies that you see with vacuum tubes that are using power tubes like this they are tie a triode connected like my lambda power supply right over here it's lots Pass tips and they're all triode connected right kind of interesting so we have a separate supply for the screens on this this is our high voltage supply over here and we have our negative voltage supply here now what I find really interesting about this whole deal here is that they have all solid state in rectifiers over here yep they're using a vacuum tube a 6x4 in the negative supply why not just use diodes over here again Heathkit probably had a whole bunch of these 6 X 4 tubes and they need to get rid of them so what they're doing is they're just giving them a service or a purpose putting them in the power supply would have been very easy to put diodes in the supply as well getting rid of tubes the six bh6 tube itself is a television tube so chances are you know Heath gets probably getting into the television scene around this and they've got tons and tons of 6 pH sixes so let's give it a purpose a very common tube and regulator service to be a control tube is a 6a u 6 so they're using a 6 b h6 in this service here kind of interesting again a lot of these tubes 0a to tubes are a very common regulator tube for many different purposes and you know Heathkit was making transmitters and receivers and all sorts of things so they probably just had scores of these things around as well so a nice tube for a reference they they glow a nice powder blue color when they're in service what I'll do is I'll focus the cam ran on some of the tubes here only part of this thing up and we'll take a look at them these will come on when this tube warms up this tube is an indirectly heated tube so it takes about you know about 10 to 15 seconds or something like that for this thing to come into a mission and then these things will kind of pop into a blue color as you see them start to work kind of an interesting situation here's something that's not talked about a whole lot and this is called filament to cathode breakdown so these tubes all vacuum tubes that have a cathode a separated cathode like this have a filament that's inside of a pipe inside the vacuum tube in that filament heats that pipe up and that's that thing that you see glow orange over a period of time in the vacuum tube not thing emits electrons which makes the vacuum tube work if that cathode doesn't glow orange the vacuum tube will not work because there's no electron travel inside that vacuum tube so electrons fly from the cathode to the plate now because there's a filament inside that pipe so basically can look at it as just a pipe and there's a bunch of a filament strings inside there and they're touching the pipe and they in the filament glows hot and it heats that pipe up Orange yet they are isolated from each other they're insulated from each other so that they don't touch now when you have 400 volts difference between the filaments and the cathode there's a chance of filament to cathode breakdown so what they've done in this case is they've tied the filaments to the cathodes and they've given all of the tubes their own heater windings so basically what happens is is they're eliminating the chance of heater to cathode breakdown and that's a really smart thing to do because if you didn't do that if you say had these filaments on just all a standard string one of these tubes is going to start arcing and sparking inside and it's going to connect the filament to the cathode if it does that at any point in time it's gonna blow off the bonding wire that runs to the one of the pins that run out of the tube there's a little tiny bonding wire it's almost like a fuse that runs from the pins to the cathode inside so this is something that really isn't commonly talked about now you can see that they've done this for all the vacuum tubes they've done this for the 6l sixes they've done it for the 6b h6 and they've also done it for the 6 X 4 and if that's not enough you even have isolated filament winding that's running out so you can have completely isolated from the rest of the unit it has its own separate entire filament transformer with four separate windings that's a really smart thing to do in some of the cheaper designs they don't really pay attention to that kind of stuff and that causes issues so in the data sheet for the 6l6 you'll see the heater to cathode breakdown voltage and that is uh a lot lower than 400 volts I can tell you that so you can see that we have AC here on a filament winding and those filament windings are attached directly to our DC output now that could be kind of tricky for those of you that are new to this this AC filament winding is isolated from everything else it's not attached to anything so even though we have AC attached to the cathodes here there is no circuit for that AC to travel so it's virtually invisible on this line so we can have AC here and DC at the same time yet because it's on its own isolated winding it's invisible at the output same thing for this tube right here the six th six and the 6x4 rectifier so you have a pilot went up across this winding the pilot lamp is across a six point three ac Vulcans out here to the little jack that says four amps on the front there now you can see that they've got some diodes here in series the reason that they put diodes in series is because the PIV or peak inverse voltage so they don't want these diodes to short out because they're basically this is well you could say back in the day when they put this thing together you know diode technology isn't to where it is nowadays right so they want to stop any breakdown from happening inside these diodes if you exceed the PIV or peak inverse voltage of these diodes diodes have jumper NV okay so whenever you see this symbol here it wants to become a jumper throughout its life it has jumper NV so any time you give a diode to turn a chance to turn itself into a jumper it's gonna do it and you know what once they turn into jumpers that's the good life they never turn back so the diode has to be replaced all right so by putting two diodes in series like this it lowers the chance of this thing becoming a jumper at some form of time now with the newer diodes you know the PIV voltage go way way way up there and you know the newer diodes you get three amp diodes and things like this is a probably really low current diodes at the time and these probably shorted out at some time again jumper NV so they turned themselves into jumpers and probably ended up popping this fuse right over here so they all just got replaced same thing with these diodes up here as well one thing that's not commonly talked about is what happens is is when these diodes short out people turn on the power supply then it immediately blows the fuse so what does that make you think okay you turn on the unit and it pops the fuse so you're thinking uh something happened when I turned the unit on to blow these fuses well there's a really good chance that at the last turn off of the unit you popped these diodes because what happens is is depending on where in the cycle this is on the AC cycle and you shut that switch off when you shut the switch off you create a spike on this side and sometimes that spike that voltage spike exceeds the PIV of a diode and what it does is it causes it to short so maybe at one point in time it exceeds the PIV of one diode so you're running on two on one side and one on the other sometime down the road just at the right time you shut that switch off at the peak of the cycle and we get another spike and it takes out that other diode and now we have a shorted supply so a lot of the times in power supplies diodes short at the last time you shut it off not at the time when you turn it on there's a bunch of different failure points so surge current and PIV are two very different failure points so something to keep in mind it's very common to think when you click that on switch that the diodes went at that point when in fact they may not have something to keep in mind now of course vacuum tubes are a lot more tolerant to you know PIV and things like that right then a you know a solid-state rectifier diode or something like that right what else can I tell you here the reason that these tubes have jumpers inside of them you can see that these are two zero a two tubes this is something that's not talked about again inside these tubes there's a jumper from pin one to pin five and there's a jumper from pin two to pin four now the reason you can see that we have the cathodes running to pin one it goes through the jumper and comes out of pin five here the reason they've done that in these tubes and most regulator tubes is if you pull the tube out this circuit stops working it's a protection device so they have a bunch of protection devices here you can see that there's a jumper here as well so they want to make sure that you are running this with both of those zero a two tubes inside here we have that nice stable reference here for this tube here so the tube knows where it needs to be to do its regulation in these power supplies you'll see that it they are using seventy micro farad capacitors rated at 350 volts very okay to use 100 micro farad no problems at all chances are the reason they use 70 again is because they have baccala box loads of these things kicking around right so it's always okay to increase the capacitance and a power supply a little bit you always want to make sure that you're always above their rated voltage this is 350 so in my case you know I'm gonna install 450 volt caps and the ones that I use I have tons of 47 micro farad capacitors so I'll probably just put two in parallel on each side right and we'll give me close to a hundred Mike's in fact I have forty sevens and 22 s I could come really close to this but again it's not important chances are they could have used one hundreds but they used 70s because they had a lot of them on hand and you got to remember this is Heathkit there's a lot of cost-saving stuff going in here to keep this affordable for the consumer right you can see that we have twenty Mike's here absolutely fine to use 22 micro farad that's a common value you can see you have 40 Mike's here 47 would be fine there we have a 20 Mike capacitor here in a 20 Mike capacitor here again absolutely fine to use 22 micro farad always exceed their voltage the same or more never go lower with the voltage very very important in power supplies and what else can I tell you oh yeah in a negative power supply you'll find these in transmitters radio receivers audio amplifiers you really need to pay attention to the capacitor that the polarity of the capacitor now you'll see in this configuration here that they have this running the the correct way all they're doing is they're taking the positive side of this rectification and they're tying it to common or ground and they're running the center tap out using that as a negative supply in many cases where you don't have the option to tie the common to ground you'll see the positive side of the capacitor tied to the chassis and you'll see the negative side running off to a vacuum tube now you need to be very careful with that that you put the negative supply capacitors in the correct way if not you'll get a very loud bang or you'll blow the bonding wire off inside the vacuum tubes on the cathodes so something to keep in mind always pay attention to the polarity of the capacitors because if you're not familiar with negative supplies the capacitors look like they're installed backwards in many cases something to keep in mind this is a voltage doubler circuit so we can see that we've got two diodes this way to dodds this way in two caps here so they are running a doubler and it is at 600 volts that is a lot of voltage there again if you're gonna work on something like this be very very careful if you're gonna play around with this you're doing so at your own risk this thing is you know got lots of voltage and a lot of current as well so this could very easily throw you across a room or worse and I'm not kidding this is there's a lot of voltage and a lot of current present at this point here scary amounts of voltage and current so you see we don't have another cap here this looks to be 20 micro fret at 450 volts across here and are pretty simple that's that's pretty much yet so our on and standby switch on the side you can see that there's only a two wire cord involved in this 400 volts set and a zero set so we would have to set the zero set of the meter and then the 400 volts sign so that it basically will go from 0 to 400 volts that's relatively straightforward and you can see that at the this is the negative bias out here so you can see there's a negative 150 volts here and then runs off too common here so between common and the negative 100 volt supply here we're not gonna have regulation at this point because we have a VR here and we also have a 22 K load resistor so that's basically protecting the circuit if you short this out it's just gonna try and heat that resistor up it's not gonna fry the VR so it's a reason that they have this in circuit here now for BIOS circuits you really don't need any kind of regulation because there's almost no load on by circuits right because it's usually attached to the grid of some form of a vacuum tube and again vacuum tubes are like fats that are voltage controlled devices so you really don't need to supply any kind of current to the grid in most applications so there's not going to be really any load here that's the reason that there don't have any kind of regulation at this point so but if you do put any substantial load on the buy supply it is gonna pull it down right so because there you know the regulations at this point and we can see here at this point before it runs through the VR so this is gonna sag at this point whereas at this point here you know we have our sense line which is technically right here so it's always going to correct on this supply so this supply here will always correct for the load that you pull across it of course until you exceed the maximum amount of load right so that's how this circuit works I hope that clarifies things so what I'll do now hey is I'll set up a demonstration of how the load works and I'll explain how this tube controls these two tubes you can look at these two 6l6 tubes like two very large voltage controlled resistors so the higher the voltage goes on the grid the more these tubes conduct so the resistance goes lower and this passes more current to this side and again this whole circuit is operating in the blink of an eye it's that incredibly fast it's correcting for any kind of current or load that's pulled over here so again the astronaut our supplies and everything the same kind of idea except these are just transistors and this is an IC that is a normal sized variable resistor this is a very large variable resistor you can see how big this thing is so this big variable resistor is going to represent these two 6l6 tubes I am going to play the six bh6 tube so I'm going to be controlling these 6l sixes get this out of the way here so across this big variable resistor I have 12 volts from end to end is 12 volts and the wiper is roughly centered in the middle at the center I have six point zero four volts and that's going to be supplied to these two leads right here this is a six volt light bulb and this is going to act as our load so as you can see we have 600 volts at this end and say we wanted 300 volts out over here so it's roughly half so we get some drop across the tubes you can see that this would be 12 volts and this is roughly half so and we have drop across this now since I have six bolts at the wiper here and I have a six volt bulb right here what's gonna happen when I attach this bulb into circuit all six volts in a six volt bulb right let's see what happens I pulled that down to 1.8 volts and as you can see it's just very dimly lit why did that happen well that's because this bulb is drawing current it's loading down the circuit so me being this six bh6 tube says hey 6l sixes I need more current so I turn those up until I get my specified six volts and that's all done in the blink of an eye just that fast now if I want to remove this load watch what happens to the voltage whoa it goes really high so again me being this six bh6 tube says hey I need to shut you guys down and I bring it right back down to six moles again and this is all happening again in the blink of an eye just that fast and the same thing is happening in solid-state power supplies power supplies that you run your ham radio on any type of linear power supply that has say past transistors and an LM 723 or something like that inside this is all happening insanely fast because you know when you're transmitting on your radio as soon as you grab the microphone or press down on your Morse code key or whatever you have it's instantly drawing current and it has to compensate for that immediately and then as soon as you stop transmitting it has to shut those pass transistors down so it doesn't harm the radio so it's a very very fast action and that's basically what's happening with this tube and these two 6l6 is here again just a whole lot faster than I can do that so there's a representation of what's going on in this power supply really simplified so what I'm going to do now is get rid of all the crappy components inside that power supply and we'll try the thing out see how well it works for those of you that want to see the backside of this VR I'm sure I'm going to get the questions there it is it's monstrous nichrome wire and a carbon brush and when I rotate this it just rubs along the nichrome wire like this so the total resistance across this big VR is 125 ohms that's from end to end so when I was doing the demonstration it was roughly in the center right giving me about 6 volts and then when I compensated I went towards the positive end like so to supply more current to light that bulb so really really big variable resistor monster-sized variable resistor handy for demonstrations and things like that and many hours later the power supply is recapped I moved a whole bunch of wiring around and cleaned the wiring up not only for aesthetic reasons but for noise reasons as well and I'll talk about that here in a bit that horrible hole that was our GERD in the backside of the chassis it looked like it was done with a can opener has been cleaned up I fit a rubber grommet in there just to cover the ugliness of that original hole worked out quite well the line cord goes through that through a strain relief over here back over to the fuse and then to the switch and as you can see that worked out really well line cord exits right in the center of that rubber grommet there was two smaller holes on each side of that really large ugly hole so I fill one of them was just a screw in and not just for aesthetics and the other one holds that strain relief it worked out really well I'll show you the rubber grommet here in just a little bit when we take a look at the tubes all the resistors check out fine everything's fine oddly enough Rayden spec now the reason that I had to move a lot of the wiring around is because this would have been a very noisy build and if it was an amplifier it would have been horribly noisy so whenever you're dealing with a chassis that's point-to-point whenever you have wiring in it like this you always want to twist the wiring together and have it tucked in a corner or or as close to the chassis as possible like they've done here so they've done this correctly as you can see they've done that here with all the AC lines that's very very important to do to keep the noise down now you'll recall with a line cord the other one that was in here there's that long white wire that ran over here into this and then there was that black wire that was patched into a piece of speaker wire that was AB strapped and then back in I don't know what was going on with that so all of that stuff just creates issues so all of that was all cleaned up now all the AC lines are tucked as close to the chassis as possible very very important in a point-to-point build whenever you have AC lines again AC lines are always closest to the chassis all the DC lines and everything else are on top of that very very important for point-to-point stuff some of these wires here I gave a few more twists and I cut some of them and shortened them up as well because some of the wiring was just a little bit too long use a bunch of zap straps to keep things somewhat orderly in here so it all turned out really well I bent the binding post back this one in the center and moved them around a little bit very easy nothing really special put a screwdriver in there and Bend it back this aluminum is so soft that it just it bends really easily I tightened up all these nuts on the backside because they come loose over time one thing to keep in mind and a lot of people forget about this is when these binding posts are screwed down tight like this you don't see the little hole that's hiding in there so you'll see when I unwind this here there's a little hole to stick a wire in and if these are all tightening you tighten these all up a lot of the times that hole will shift the whole you know binding post moves over and there's nothing worse than trying to fit a wire into a binding post and you know you find the hole is going this way and the binding so what you do is you make sure that the binding posts are all up and down so you can stick a screwdriver in there so you'd stick a screwdriver in there like so and just hold this in place and then tighten the nut up on the backside here and that'll just make sure that this stays straight up and down and then you can move to the next one and if it's a little over you know put the screwdriver in and then move it around and then tighten it up like so and then that way you don't have the frustration of having to try and find a wire feet of wire and sideways and stuff like that something that's really commonly overlooked with these binding posts and this older equipment like this this is that grommet that I installed in the backside of the chassis to disguise that really ugly hole and as you can see it doesn't look all that incredibly bad sure looks a lot nicer than that hole I can tell you that much so they've put a lot of getter compound in these regulator tubes and it's hard to see that purpley blue glow but if you look in this area right here on this tube this one right in the back here right in that area there you'll see that start to glow once this rectifier tube warms up so what I'll do is I'll just turn the lights off here and I'll turn on the power supply so keep an eye right on this area right in here there you see it's glowing now a lot of these regulator tubes glow very bright some of them don't have a lot of getter compound they look really nice but you know more getter compound the better so even though they you can't see that purple glow at least they're doing their job and they're doing their job well there's another one of those tubes right behind here if I move the power supply just a little bit you might see that purple glow of that one as well you see that in there right back in here so some of the really large regulator tubes they have an orange glow to them they look really neat when they're operating so it's kind of basically two glows there's a powdery blue kind of a purpley glow and an orange glow regulator tube the orange ones are a little bit lower voltage than these ones here let's try out the power supply and see if it works so the moment of truth has arrived click it on to stand by and let it warm up for a moment now before you do an alignment on something like this the thing really should warm up for a while that's really important so you can see even with it in standby there's a little bit of voltage there to see what happens with that that's kind of interesting okay the tube should be warmed up so this is rate down so this would mean that I need to adjust that zero set on the backside there so there's two VRS on the backside so I'll adjust that zero set until this sits close to zero volts I'll just move around here hopefully I won't bump the camera and stuff very touchy control you can see this would take a little bit of fiddling close enough for now all right so that's a zero set and that's with the VR right down at the bottom here so now I'll start turning this up and voltmeters accurate it's pointing right at 100 and it says 101 up to 200 volts no problems there 198 I move this just a little more I'm standing right in front of this so I can see how accurate that needle is and get it just right on top without the rate there's right on top of the line look at that 199 very accurate meter I would say that line is right on top of the 200 line let's go to 300 looks like they me here might be a little sticky move this around a little bit probably hasn't moved in a long time that's no problems now no issues all right so that's about right on top of 300 dot bad 297 and I'll bring this rate up to 400 volts right there and that's right on 400 volts look at that so now the 400 volts set is supposed to make it top out at 400 volts and see how much further I can get four hundred and twenty volts is fine if I use an external voltmeter I kinda like that little bit of extra I would really like this power supply too if it would top out at say 450 my other power supply my lambda it's it tops out at 500 so 450 I think the reason that they did this at 400 is because most of the larger capacitors they top out at 450 so they probably don't want you to get too close to that that might be the reason so actually gonna leave that just like that so 420 is just fine I'll leave that so it goes over 400 a little bit and then when I go back down it should go right to the zero so that's right at the stop right there point two just fine you know I could fiddle with that control and probably get that rate at zero point zero something or other so not bad I'll bring it up to 300 volts actually let's take it to 250 250 volts and I'll give it a load and watch the current meter come up here and we'll see how much drop we get I wouldn't expect much more than a volt or something like that with this power supply it's probably gonna be pretty good so 248 and here we go two forty seven eight yeah so really that's fine look at that so let's turn this up let's get a lot of load going here that's the co but we're gonna have to test that to bring it up to 100 mils so that's the max that's supposed to go into that's on the red line so so 374 will say 374 right now and 100 mils of load not bad that's rated the max what two volt drop well volt in a bit anyways and that's a lotta low you can hear I don't you can see that in them plug they're arcing away arcing away in there so not bad so what I'll do is I'll bring this down to say three here to 200 volts that see how much drop there is at 200 all right here we go that's 50 mils so there's 196 and yeah still 196 it's within a volt so it's staying within a volt so as you can see as we get closer to the top it starts to pull down just a little bit more but that's fine for this power supply this is working absolutely great if I really wanted to critique that I could adjust that divider that I told you about I could most likely play with this divider here this divider this resistor in this make a divider here I play with this value and even this value here I could probably get that extremely accurate and then of course moving this closer to the output Jack would pretty much correct that you see it looks like it's on this side of the meter too so if this sense lead was right at the output Jack there might be almost no drop that would almost be something to experiment with so it's working very well when you're dealing with this kind of voltage in that little drop it's working extremely well I'm very happy with this power supply so all in all it turned out quite nice so what I'll do here is I'll try out the C supply which is the negative bias supply so I think those two are hooked together I'll just move this over here turn that down so we should have negative voltage here now if I move the meter switch over here should read that look at that no problems 127 volts a little over 125 there hundred volts right there working very well everything is working great on this power supply I'm extremely happy with the results so we could test one other thing which is this heater supply now that's obviously going to work so we'll turn this to AC volts here and this is down this is down I want to make sure everything is down before I go about moving anything here and I can just plug this in on the front I don't want the meter to move let's try this AC volts there it is 6.8 a little bit high that's fine because it's not loaded right this is an AC supply no problems project successful thanks for stopping by the lab today I hope you enjoyed the repair and explanation of this power supply if you're interested in repairing and troubleshooting power supplies audio gear test equipment radio transceivers radio receivers and Men more electronic devices you're gonna want to check out my super troubleshooter series on patreon I'm teaching everybody how to troubleshoot and repair the way I do so if you're interested in increasing your skill set definitely check that out I'll have the link just below this video and I'll also have that link pinned at the top of the post if you enjoyed this video you can let me know by giving me a big thumbs up and hang around there'll be many more videos coming like this in the near future we'll be taking a look at many solid state and vacuum tube devices alike so if you haven't subscribed now it'd be a good time to do that as well alright until next time take care bye for now you

Channel: Mr Carlson's Lab

Views: 100,953

Rating: 4.9556518 out of 5

Keywords: power supply repair, powersupply repair, fix power supply, rebuild power supply, tube power supply, linear power supply repair, high voltage repair, power tubes, learn to repair electronics, fix electronics, restore electronics, vacuum tube repair, electron valve

Id: JroiDZgReak

Length: 58min 42sec (3522 seconds)

Published: Thu Aug 30 2018