This 1959 Kay Tube Guitar Amp Design Is SHOCKING!

ladies and gentlemen this is amateur repair time back with another cool guitar amp repair video for you this evening now if you didn't see our other ones we've I've worked on a couple of these on this channel um this is amateur repair time so we're going to do an amateur repair of this uh amp I bought this online it's an old tube amp little Cheapo but it's a tube amp I guess from the 50s and um guy said it blows the fuse when he turns it on ooh that sounds fun to figure out I couldn't resist so he packaged it up and uh shipped it to me and here it is um so we're going to look in it see if we can figure out why it's blowing a fuse and see if we can get it to work what do you think about that instrument inputs we can get a whole band going instrument volume tone control you can turn the oh the look the tone control is the off one you would expect that on the volume but you would be wrong 120 volts 33 Watts quarter amp 50 or 60 Cycles okay so let me take this off and I think he's got the tubes in there for us so that comes off of two screws the gentleman has put the tubes in a little package for me so I don't get messed up this is it's a name brand one but it's a cheapo name brand I can't remember it's not a silver tone it's like a k or a Vox or something let's see what it says license notice AT&T how to order parts for your guitar amplifier well we got a nice little um we've got a nice little list of everything for the Bon company is that what it says as model number 803 here are the three tubes 36 a something or another 60 fx5 does that say 60 and then 18 gd6 okay let's see if we can test those there's the three Jacks there very simple little amp if it's blowing the fuse though might have a bad Transformer so I don't like that and what fuse is he talking about I don't see a fuse in it but we can work around that pretty wild it's a Widow Maker I think I don't know there two there's output Transformer and what is the T1 here it's not giving us any voltages we'll figure it out okay so um yeah that's what we're looking at so we're going to have to go in the thing before we try to plug it in or anything so let me get a um maybe we see if we can test the tubes first to see if his problem was he had a really screwed up tube well if it's the tube though I'm going to end up messing up my tube tester H all right well we'll test the tubes first just for the the heck of it if I can test those I've never even heard of any of those three all right so the first one is a 13 a63 I mean a 36 am6 3 36 am 3 no 36 a3c is what this what mine is so I've got it all all set up let's see if she'll do anything I'm going to go with it's not great nothing I must not have it in the socket very well there we go it's actually a very good tube but that's probably because it's just a a rectifier if I was going to guess you know on tube radios a lot of times you have the uh uh um 35 rectifiers that's a 36 I'm just going to guess that's probably what that is all right so on to the next one that one seems all right all right so I was wrong again it's a 36 am3b all right not C all right so this one is a 60 fx5 so I've got it [Music] um hooked up this the heater voltage will only go to 50 on this tester so it's telling me to to set it on 50 we'll see if we get anything yeah so another good tube you know this is good that we're testing these because I have yet to see many tubes that I have that test this good on this tester most of mine always come up to like 50 60 every once in a while you'll get one to 70 so this is good to see that at least there are some uh you know output tubes or whatever that is that do test good on this tester on to the next one all right and the final one there's only three tubes is an 18 gd6 a so it's volt the heater voltage 18 the sensor the sensitivity 80 socket one test button one uhhuh yeah see that's what I'm more used to seeing on most of my other ones we'll get something like that so that one's marginal but I haven't seen it telling me there's any shorts so uh and you know it would be hard for the tube to blow the fuse there's probably a screwed up resistor or the Transformers bad or something in it so I think all three of the tubes are at least usable although this one is kind of weak all right so the tubes seem at least usable like I said and the uh they also are inexpensive I looked them up they're not that expensive the uh 18 GD six that we were looking at 18 GD 6A is just a preamp um okay so take two screws loose and this thing comes out and I've very carefully set it here where the speaker is still hooked up the tubes themselves would Mount here and then there's a plate here we got to take off next okay so I took the screws out I haven't peaked yet uh the gentleman I got it from and you know even these little cheapos are not super cheap now so I paid a little bit for it but uh the gentleman I got it from said that a it had been serviced by a guitar guy an amp guy so let's see we'll look together at the horror I'm going to guess some kind of burnup connection on something because he said as soon as he plugs it in it's blowing the fuse so we'll see what we got going on the guy that he got this from or the guy that he had work on it um he said uh serviced it now I understand it's a guitar amp so a lot of times the guitar amp guys and girls they want to keep these old caps in them because of the sound of the caps but I don't know that that's the Great greatest idea so obviously the fuse here is blown so there was a fuse installed in line um new power cord coming in neutral running over to one of the pins of what I would assume is the rectifier tube uh hot coming through a fuse you know the flaw of this is there's probably your problem right there that's a bad idea what's on the back of this thing metal you would probably see it though if it had shorted out maybe that ain't a good way to do it folks I don't know why you would put that fuse up in the air where it can just touch the you know the live voltage running through that touching the plate okay and then at the same time the plate oh yeah the wire just hanging there right but you just touched hot to ground through the plate so that's probably what's going on maybe he's been back in it messing with it and there's some stuff unhooked I mean obviously that didn't hook there so we're going to have to look at the schematic and see what the what the guy was trying to do see the yellow and the purple wires that he's added um on the video here it's looking like those are close to touching things they're not it's just a he's glued the Caps to the plate I don't know what would have been there originally I guess a can capacitor was mounted um so it's not we may be able to leave those as they are I mean it could have been done a little cleaner but it's not the end of the world uh and they're kind of protected the plate would go over this part you know so that's probably not that big of a deal got an old school cap here got two Ceramics and an old school cap here I wonder if this came off of something and that's our problem like that broke off something you know and then fell inside the cabinet grounded it to here soon as you plug it in you've got the Caps Wham okay um yeah so we need to look at a schematic and see where this goes okay so I am looking at the small schematic AC outlet coming in the bottom the hot runs directly to the uh the rectifier and then goes from there you know the rectifier is going to create the B+ the negative is actually what's switched off and that you know that's pretty common so the negative runs through the switch right and then you can see that the negative runs up here and cre creates the um the B minus basically and you can see over here where the Jacks Are is connected to chassis and so the Jacks are connected to chassis and the input to the preamp is connected to chassis and then you get and there is a resistor R7 which is a 470k 47k resistor and you get a capacitor C5 right and those turn this chassis ground they isolate it from the B minus which is here okay the capacitors so the the um the rectifier is creating our B+ voltage up here this is B minus this is B+ dropping resistor plate voltage for the output no the preamp the plate voltage here is coming from that okay so the the reason it looks weird is because of this this is not this this is the ground for all three of those caps so this is B minus this is B+ because it's coming off the rectifier and then this is plate voltage because it's dropped by the R11 this whole part here is actually isolated from the chassis by this resistor and this cap right so all that to say that's not how they've got it hooked up they've got the hot coming in going in through a fuse and then running to the onoff switch and then being switched into the B minus which would work because in the wall you know you don't really have a hot and a ground really you know you do but you don't really so um they're defeating their whole purpose of putting a grounded plug on it they're sending the hot into the switch and then into B minus and then the neutral is what's going to the rectifier so this really should be up here and then everything's wired properly and this should run through a fuse and then down there and the reason that they did it this way is so that whenever you turn off the switch you're turning off the the hot but the whole sets wired backwards I guess it I guess it doesn't matter but it kind of does whenever you get to that point where you have the resistor and the capacitor isolating it from the chassis so I'm going to go do some research to see if that's how most people do it but I I think you'd be better off taking this loose so you could leave this how it is take this loose and then run a line from here to here so that the switch turns off the entire um rectifier right and then hook the neutral to this that you would remove from here so the neutral is running down to here so you could tie the neutral in there um this is the capacitor and the resistor that are isolating the B minus which is this from the chassis which is the pot um and the three inputs all right let me go see if I can find a better schematic all right so this is how people are modding them now you know this is all safety stuff so don't do any of this don't just don't even mess with these it a be illegal to mess with them right so what the what the people typically are doing oh there's two things you can do they're taking out the across the line cap here because basically that cap and that resistor are like I was saying isolating the B minus from chassis ground well the problem that that runs into is chassis ground is connected to uh the guitar chord the guitar cord is grounded to the pots on the guitar and the ponds on the guitar are grounded to the tail piece on the guitar which is holding all of the strings which you're touching with your fingers right which is fine because it's all grounded but the problem is if that cap were to short now you've got the neutral from the wall connected to it and as you know in an AC circuit it's the neutral has voltage on and they're scared to death of that um on a you you run into this all the time on the um tube radios they they've basically floated the B minus above the chassis with a resistor and the cap that they are not showing here anymore it's a 04 microfarad cap um so on a on a tube radio if you leave it the way it's originally designed you replace that cap with a safety cap because the difference between a safety cap and a regular one is that the safety cap whenever it fails it never shorts it fails open they're designed to not be able to short the problem with it shorting is again you would have voltage from the wall through that cap if it were if it were to short touching your fingers right and they call it the Widowmaker and the guitar players are scared to death of it um and then over here on this circuit they have drawn so basically they've removed that cap so it can't short if I was going to do it this way I would replace that with a safe cap that won't short because you need that cap for to keep buzz off of the signal um and then here's what I was talking about they have the fuse right here that's not where that's that's not a good way to do it so the fuse should be between the um the load and the uh heater on the rectifier which is just a halfway of retif fire apparently so the reason that you have to have that you're adding that instead of over here is that the set is still has power running through it and if the cap were to fell the whole chassis would be hot even with the switch off so you know there are safety considerations here me personally I'm never going to let any body play my guitar amp Sol Mah right but so what they're do what a lot of the guys are doing is they're adding an isolation Transformer here and hooking up the switch on the other side of the isolation Transformer that way the whole chassis is isolated from the wall the voltage in the wall oh you're going to love this you're going to tell all your friends okay so what I've done temporarily this is not per temporarily I replaced this one cap uh this one I've left for now I got to look up what the spec of it is so when I bought this the guy said he had it he sent it to a guitar guy the guy got it working he played it for a while and then he turned it on one day and it blew the fuse okay my theory is is because the fuse just touched the the chassis right so you saw how the schematic is this is the 47k resistor that isolates the chassis from the B negative I'm calling it The B negative or maybe a better term for it I put this safety cap in to replace the one that was in there so this is what was in there a 0.04 microfarad capacitor these are always scary looking whenever the dis ones like look like they were coming apart but I don't you know you're going to love this so what I did was I hooked the hot I just hooked it back up how it was originally I hooked the hot temporarily see how I've just got it twisted to the uh heater of the rectifier which then loops around as the input to the rectifier to halfway Rectify it right and then I hook the neutral to the switch neutral to the switch and so then I hooked the the this side already had the B minus wires and so I hooked the B minus of the filter capacitors right there it's a good tie end point they had the hot going here I don't know where they had this going it may have been going there too but it wasn't soldered very well if it was so then what I did was I put the tubes back in and I now keep in mind there's no fuse in it now I just put it back how it was originally and then I with it unplugged turned the volume on turn the power switch on and turn the volume halfway up and then I plugged it into a a circuit protected power strip and turned it on and it came right up so but let me show you this is the part you're going to love this is cray cray so I'm G to turn it on I'll turn it up so you can hear some voloom we should hear some hum here somewhere my tubes are glowing on the other side let him warm up a little bit can you hear it that's the this one's [Music] tone no this one's tone this one's volume you hear it so we're up okay now here's the crazy part ac voltage 123 volts coming in which means that it's going through the switch I'm trying to do this carefully obviously 123 volts it loops around over to here 123 volts now here's the fun part 123 volts on the chassis however not really what's happening I think is the meter is picking up the little teeny tiny bit of current that it can get through this resistor and cap set up right but if you check it with a meter that thing's live but it's not really live so I plug the guitar into [Music] it [Music] this one is actually volume that one's tone it's just weird but it's only got her clean tone and just a kind of tone down [Music] tone [Music] they say Keith Richards really LED this same guitar amp I don't know why [Music] but [Music] uh that's why people are afraid of this thing if you check it with a meter the voltage is on this but you can you can touch it I'm not scared right I don't feel any tingles or anything but there is live I'm 6 in away people it just looks like I'm touching it there is live voltage going through that resistor just a little bit to where a meter can pick it up so what do you think safe or not safe so people put an isolation Transformer on it the the point I was trying to make a minute ago I don't know if I edited that out an isolation Transformer doesn't make it completely safe you can still get the hell shocked out of you if it's running through an ISO it just it makes it a little bit more safe right but just cuz you've got an ISO on it doesn't mean that that you can't get shocked cuz the the your basically it's it's basically making it where you're not grounded anymore to a separate ground so like if I were to touch something in this room that's grounded or even be grounded through the floor or something and the chassis was live I'd get a shock so the iso gets rid of that but it's still got voltage running through it if that if if you've got the same thing going on so anyway all right I'm checking the amperage and it's like 0.1 amp something like that I mean this thing just it uses no power um so that's off you can barely see it you see a little in Rush when you turn it on so I'm just trying to figure out the the uh fuse I think a 0.5 amp fuse would be great because you're getting nowhere near that you know so so yeah 0.1 what what would that make the wattage on this thing like 15 watt or something it's it's like a 10 watt or 15 watt amp maybe this is the fuse that was in it let's see if we can figure out what they chose to put in it I can't read it maybe I can zoom in sometimes when you zoom in it makes it easier there we go and a half so so they used a one and a half one and a half and that's a Slow blow you can tell by the thing inside so it shouldn't ever get anywhere near one amp um it does say on the on the back of it that it's a 35 watt and that it's a275 Amp but according to my amp meter it never gets over 0.2 but who knows all right so that's how I ended up with the fuse holder in there we got it shrink wrapped in line with the hot the hot lead um remember that plate goes over it I'm going to put a little we're turned on by right now by the way I'm going to put a little uh connector on the end of this and then attach it right here whenever I put that plate back on that goes on it um and uh I left that one cap because I started looking at it and that's just all that's going to do is have something to do with the tone you know the the the signal comes in there so it's between the signal and one of the pins on the um preamp so I don't think that if even if that shorted it wouldn't cause any trouble it would just change the the tone of the guitar so um but with the ground line and with the fuse properly put in and with the the it all covered and everything I think it's safe or at least uh as safe or more safe than it was whenever they built it so I'm cool with that for my personal use now you you may want to put a full isolation transfer forer in it so that's the the little power transformer it's not really an isolation Transformer but it kind of acts like that for one of the heater voltages if you look at the schematics and then of course that's the output Transformer on the speaker so I'm cool with it like this doesn't bother me at all and um that's how I'm going to leave it so we were able to get her work working pretty uh pretty easily I think I honestly think what happened was the fuse just touched the side of the of the thing it could be that someone was trying to update it to make it more safe and you saw how they had the hot to the neutral which may have worked because basically you would be doing the same thing if you plug the the uh wire in backwards uh but it it looked to me like that metal fuse that just shorted out against the the frame of the of the uh enclosure so I don't know why they were doing it like that but these little things are only like a dollar I've got a whole bunch of these that I use at work sometimes so um so let me button it all back up and we'll see how it looks after we've got it done okay I got it all put back together it's pretty ugly a little beat up one of these days I might put new covering on it I don't know what they call that stuff but you know I hate to take the original stuff off even though it's pretty rough I don't really mind it's got a little bit of noise in it cuz I've got it all the way up we're on 10 it won't go to 11 and then this is interesting to me that the on off is on the tone so if you turn it all the way down but not off um I got a guitar here with a little bit hotter pickups it basically takes all the highs [Music] out and then as you turn it up you get more [Music] highs right and if you keep going with the volume all the way up it actually gets [Music] distorted so this it's got a cool little almost built-in Distortion just by cranking it all the way up it'll start overloading a little bit depending depending on the guitar you're using and uh that's kind of clean I can adjust the guitar tone [Music] knob [Music] [Laughter] [Music] [Music] [Music] [Music] he I could see why somebody would want to record with it because you can just crank it up and it'll distort and you can you can get several different styles out of it you know so if you I don't know how to play but if you know how to play you could really make it sound pretty [Music] good [Music] all right folks so I think it's pretty cool I like it neat little amp consider getting one if you're not afraid of it we'll see you on the next video by the way if you want to see another amp repair video that we did check out the one there on the left of your screen we'll see you on the next video hope you enjoyed it