Old 1960's Barn Find Radio Receiver Teardown And Diagnosis!

hi everyone welcome to another episode of Mr Carlson's lab today on the bench is another barn find radio receiver it's a 1960s 1970s era AM FM radio with vacuum tubes inside it so let's see if it works I have no idea if it doesn't work we're gonna make it work not a big deal so we'll tear the thing down any way we look at it and see how the thing works so let's plug it in and see if there's any life and proceed from that point all right here it is in all of its Glory nothing has been touched since the barn as you can see dust everywhere and it's just sat on the Shelf so that we can go through this thing together so this is the back side here the reason I know it has tubes in it is because of this right here a little piece of it is missing I'll just zoom in on that for you so you can see the tubes so I find it interesting that they just kind of scratched out some numbers and then stamped The Replacements on here kind of an interesting thing that they've done there you'd think it would just be cheaper to print a whole bunch of these things off with the correct numbers on them but whatever I guess the stamp worked and uh yeah it's in relatively good condition for incredibly hideous looking radio that it is so uh hey if the thing works all that much better if not I'll make it work and uh who knows this might just sit off to the side here in the lab and play some FM for me when I'm working on stuff on those quiet evenings who knows whatever right so could definitely use a cleaning that's for sure all right so what I'll do is I'll get this thing plugged into the isolation Transformer and variac Supply we'll turn it on see what happens and go from there isolation Transformer and current limited variac Supply this is plugged into it and this is in the off position both of them are so I'll turn this on so you should see a very dim glow on the bulbs which means that this whole thing is working right now but this is still off so when I turn the switch on these should get bright and then go down a little bit so let's see what happens absolutely nothing so that means that this radio has no life in it right now so something is wrong inside here so that gives us something to fix as well as tear down so I'll shut this off and let's get into this thing and find out what's wrong with it to get inside this thing looks like we have to remove this screw this screw this screw and this screw and there are some on the bottom as well so one here and one over there so let's see what happens looks like the whole thing might just come right out of the front side so let's find out all the original dust on this oh let's just remove these screws and see what's going on so you can tell this is from the years when they started to take safety a little bit more seriously they have an interlock on here like they did with the televisions and uh oddly enough they are using series set television tubes in this so they're probably again a cost cutting method that's what it was all about way back when is of course selling a product that works and at the same time giving you what you want and them saving some money it's still about that nowadays except it's kind of changed to them just saving money and giving you junk that's what's going on nowadays it's really hard to find quality anything now so looks not too bad inside right you know the original dust here and all that kind of stuff I like that early circuit board design it looks nice a lot of people frown on these early circuit boards you know what they're still intact now and it's what 2023 right so let's remove these and see what happens all it can do is just make things easier right it'll be easy to identify because they got washers I don't know if this has ever actually been a part because most of the parts look to be here and let's see will it fall out well we still got this let's see what this does it come out of the back does it go to the front what's going on with this thing so this is all loose now so it obviously wouldn't come out of the back because it would hit here unless it tilts oh it does tilt there we go that was a good call hey look at that that was pretty easy to service is to get into so we've got a bunch of tubes here one here and we can see that one down in there one over here here here here here and over here in the FM tuner so I will now we'll get a plug I guess I'll just leave that in there I'll just leave this in here I'll get another plug with some clips and I will plug it in and see if we have any glowing of the tubes which I'm not thinking that we will because uh the bulbs didn't change so I'll get that underway be right back I have the radio now plugged into my isolation Transformer and current limited variac Supply with my little cheater cord here you see the two bulbs are lit up again and the first thing I want to do is just move the tubes around in the socket just to see if they're you know just a bad connection or anything like that first so just wiggle them around a little being careful not to touch anything other than the tube the gloss tube and that one around that one and I'm looking for obviously a brightness change in the bulbs right that's why the bulbs are in the shot here this one around over here by grabbing a glass tip on it and there is no change so that kind of tells me that there's either an open connection in here or one of the filaments is open that's what we need to look into next all right the supply is turned off so I can just grab these and take that off there that out of the way so this looks like this is held together in a very interesting way looks like this has already been taken apart like this has actually been soldered to the top portion of the speaker this copper type chassis usually it's copper plating is uh looks like it's been soldered up here but somebody's removed the solder so obviously this has been out of the case and it looks like it might be held by that one screw right there and then of course the knobs on the front are going to uh add to the fun of getting this apart right that was actually very easy a little too easy if you ask me okay so I'll grab a screwdriver here hopefully this will fit in there it does move that so that's probably that there now I have to figure out how to get that it looks like it's like some sort of an interesting clip maybe the reason that this is here is you can pop something in here to kind of pop that back so let's see if that's true looks like it is trying to come out it's not fighting all that much either this might just be coming apart a little too easy usually there's a catch never lets you get away with stuff that easy let's see something is kind of catching a bit hopefully you can see all that you don't want to force this right maybe stuff is catching on the bottom now I have to be very careful because this here might actually have a charge on it it looks like there is solid state rectification here so I'll just move that down a little bit that looks like a little solid state rectifier here it's a little diode and this could be charged up I really don't know so I want to be very careful around this area it is trying to come out but it is catching on something which I don't know what it is catching on oh it might be catching on this little clip right here let's see it is it's catching on that clip there's a little piece of plastic inside there that's catching on that so let's see if I can get that clip out these little brittle plastic cabinets are always like a scary thing don't want to crack the cabinet finds you the radio really isn't a show stopper is it that you know let's see here very difficult to do this on camera it's catching on something [Music] there it is you see how there's coming off so I'll pop this in here move that sideways a little bit without wrecking everything okay maybe we'll have some walk now haha look at that success all right looks like somebody's definitely been in here all right let's see if that is still holding a charge if it is hey I've got my probe Master probes on my meter today these are the best probes I'm telling you okay so let's see here try to fit all of this in charge on this fitting in there it is fitting in there can is negative and we are on DC look at that 144 volts 144 volts and this is the danger with these things so give me one second and I'm going to go and grab my capacitor safe discharger and I'll show you how that works and I'll be right back all right here's the safe capacitor discharge box that I released on patreon quite some time ago all the plans to build this are up there now depending on what direction I attach this one of these LEDs will glow and there's an array in here that will discharge the capacitor safely and when the capacitor has run out the LED will stop glowing so at least it'll be below the forward of the LED see that light up and that's pretty much out so it's drained that off and of course these are connected together so drain them both off right so they're connected together through the circuitry so there we go so now I know that it's definitely safe to be working around that's the kind of stuff that you have to be very careful with with any Electronics this old or new the even new stuff has got very large capacitors in it so we'll just check this again with a voltmeter and as you can see we're 0.9 of a volt and through dielectric absorption you can see that it's climbing again so a lot of people think that capacitors are just self-charging they're not it's a thing called dielectric absorption and this will read roughly the same so 1.4 so in a case like this a lot of the times it is good this won't charge up very high but what will end up happening is uh you know it'll it end up coming to a certain level which won't be too incredibly high and it'll just sit there and kind of come back down again so I can tap it one more time with the uh capacitor discharge device it's probably too low to make too much of a LED yeah just a little bit of a flicker there so one of the things to pardon the pun Rectify this problem is to just short the capacitor out while in use the only thing is if you're concerned about that this won't charge up very much anymore but if you're concerned about that you can't forget to remove the short circuit before you try to power it up again that's the only catch and that was my voltmeter tipping over over there so anyways so uh a very handy tool to have around so this even has carry through leads on it so uh the capacitor discharge device has carry through leads that you can plug into a meter so not only can you discharge it with the box but if you're concerned if you want to see more information than just LEDs you can attach this right to your volt meter of whatever you have digital voltmeter analog volt meter whatever vomvtvm and you can watch the um watch the LEDs go down you can actually see the voltage drop as well so that's all part of this box now I myself I don't use this very often I just watch the LEDs until they extinguish and then keep the probe leads on for just a few more moments and then usually it's drained enough that I don't have to worry about it so that is a perfect example of a capacitor that stayed charged for quite some time and this capacitor has got to be pretty good at least one section in it is we know for sure because how long has this thing been unplugged now and it's still 140 some odd volts on there so that's uh that's doing pretty good so I'm beginning to think probably open filament so anyways let's start testing some tubes let's start with the most common tube in the world 50 C5 so 50 is the filament voltage so the five zero C5 the two first numbers are the are the voltage that it takes to light this tube up so let's pull that out of there and that's an interesting tube socket not much of a tube sock there I have to zoom in onto that in a moment and check that out so now pins three and four on a tube like this will be the actual filament pin so what we'll do is I'll just get this under the center here and try and show you what I'm talking about so you always count this way from the index so in the center of the tube is the index this opening here so you count one two three and four three and four of the filament pins so we should have resistance on these pins if that is any good whatsoever so the focus back on the meter up here and I'll see if I can steady this up enough to get this all in here so you got one two three and four and we have resistance there about 60 ohms so no problems so we know that this one here is okay so we can put that back in but first I want to show you this really odd tube socket and I'll just zoom in on this a tube socket it's a completely Hollow underneath there's nothing there it's just a bunch of legs that seem to be standing up right off the printed circuit board maybe the filament pins are broken on the bottom you know that might be our actual problem right there come to think of it I think that filament pin is actually broken and when I'm putting the tube back in they're relying upon this connection on the bottom side of the circuit board right here to hold the pin steady on top look at the pin the the connection you see right here let's get this out of the way okay I'll wiggle it from the bottom section here I'll just uh put the focus on that look at that see that that's why the tube isn't going back in because every time I put it in this thing's pushing out of the way so what I'll do look at that it's actually turned around in there so that's definitely a bad connection that might be the reason that the tubes aren't lighting up right there very tempted just to change that entire socket oh what a bad looking socket I've never seen anything like that I wonder if that was just a cost cutting method or something like that see if I can get the tube in here straight enough to uh actually hold that okay so it looks like it's holding it now I know a lot of you are going to be saying you know oh that's dangerous for the vacuum tube to be putting solder on the pin of a vacuum tube or on the circuit board while the tubes in the socket you risk harming the tube no you don't so I've done this so many times I can't count so put the focus back on that there I'll heat up my soldering iron and I'll touch up these connections here and we'll try it again maybe that is the only issue we might need to go on the underside here and resolder all the tube sockets it's looking like a lot of the pins on this are created actually you can see this one here is created right around there as well so it looks like a part of the tube socket's actually broken away I think that's what's actually going on with this that's why it looks so strange so maybe I should just replace the tube socket but for now let's just see if this will make things happen it's kind of fun to do from the side of the camera so let's see if that brings us back to life attach the cheater cord again I gotta remember after this again if you were worried about dielectric absorption this would be the time to you know remember to remove the short or you'd have some big issues okay so let's see what happens I'll back this out and we'll take a look up here see if if that's going to fix our problem all right so pardon the focus for just a moment now let's uh take a look at the bulbs here I'll turn this back on and see if we get that bright and dim sort of thing happening here we go not much maybe that didn't help much lights down no tube action down on the bottom either so back down here again and still nothing so we beyond that we still have a bad tube so that'll be the next thing so let's keep on testing filaments all right back to testing filament so get rid of this this is disconnected again just because I'm going to be poking my fingers around in here do this again real quick see how the little LEDs there all right it gets rid of that I don't have to worry about zapping myself yeah okay so we got uh two diodes and a triode inside this tube that's what's inside here so we try out here and we have a diode there and a diode there you're probably using that it's the FM thing called an FM discriminator circuit probably anyways uh so hugely on these tubes pin four and five are the filaments so on these tubes so we got one two three and then four and five so we need to be looking at the the meter for Pins four and five so one two three and was me touching the leads together ignore that that's four and five one two three four and five and it doesn't look like we have anything do we if we have anything to nine anything to nine so let's just take a quick look inside the glass bulb here we'll be that so you got one pull this out about here two three yeah four and five those two pins right there I'll do so I'll try and hold this steady so that there and that there run off to the filaments and five that's what I just tested and this has an open connection so this is a 14 gt8 so 14 volts and then Factory identification number and eight useful internal components or you know sometimes you can look at it as eight connections so 14 gt8 so that's a pretty special tube I'm gonna have to go looking through my stuff to see if I have a 14 gt8 or so sort of equivalent I recognize the design in the six volt series but not in the not in the 14 so I'm going to go do some tube hunting and I will return I spent hours trying to find this 14 gt8 in my tube stock and since I'm reorganizing everything in the shop moving everything around and all my tube stock is all over the place right now this is unobtainium so I started doing some research about you know Crossing this tube to something very similar and I found that a 19 T8 about there a 19 T8 is very close what's very important is the heater current is the same in order to make sure that all the filaments light evenly so the heater current is the same the voltage is just a touch higher which is not a big deal from 14 to 19 volts right we're not dealing with anything that's uh going to be an issue at all in fact it'll just make things run a little bit cooler if anything so anyways this tube here let's open the box up see if it's the original it is Roger's tube that's nice I find a lot of people over time they throw old tubes into the tube box and you find that you have you find an old tube in there so this is a brand new tube so this is the uh this is what a 19 T8 looks like inside compared to uh 14 gt8 so there's two diodes in here and a triode within this shell right here so the only difference is that internally they're wired a bit differently so the triode which does the amplification in this so that you know we can get some audio out of this which is the you know the preamp for this tube right here that's all wired the same and one diode is the same the difference is the other diode is completely different so if I grab the paper here so if we take a look at the 19 T8 you see we have one diode here and then we have a diode plate here which is one of those little plates right there a diode plate here and then the cathode that's you know I come into those both of those plates is this cathode here whereas on the original tube we have two completely separate diodes with two completely separate cathodes and then that's again completely separate from the triode itself so I'm going to need to make this tube work with this circuit here which shouldn't be too big of a deal basically I'm going to be adding another diode into this so I'll probably since this already has you know solid state components in it it has a solid state rectifier and it also has a solid state detector diode right down in there you can see I'll just add two diodes into the FM detector ratio detector circuit here and that should make this thing hopefully operate as the next step okay so I still need to plug this thing in and see what happens and we'll experience that together since that's what this is all about so I'll get the line cord hooked up and everything all hooked up and uh we'll plug the tube in and see what happens see if we can get any am we should at least get am I know for a fact we won't get FM with this tube until I put the diodes in all right I've got the line cord attached back up again and I guess what we should do is put that tube in that would definitely be helpful wouldn't it like this here put that in and since I'm going to be moving some dials around I should put some knobs on this thing I guess and make things a little bit easier so what we'll do is we'll take a look at the variac here and we'll see what happens now when we turn this thing on Okay so we'll look up here I'll turn on the variac make sure it's on current limit so okay so there we go and that's what it should do you see it brightened up a bit there and then went down so I'll just leave everything attached here I'll turn the volume right up make sure the variac is right up which it is okay oh also so you know between the last shot and this shot here that you're seeing has been a few days just uh again sorting things and moving things around in the shop making more room to move stuff from Lab number one or the original lab to this lab here so I'm still moving stuff and uh it's very time consuming so I've been down here and worked on some other stuff in in between as well okay so let's see what happens here oh I do hear I hear noise say uh where's it oh yeah listen to that we have life see what happens get my hand around here oh there is a station in there arm out of the shot there see if we can find anything down here there isn't much so the lab is uh foreign somewhat below ground here so what I'm going to do is I'm going to get a loop with my 369 antenna and just put a loop of wire across here and that should couple in some signals from the outdoors into this and we'll see how well this works all right so I've got the coaxial lead running up to my antenna connection which runs to the 369 antenna which is an absolute fantastic antenna so that there goes out to the 369 antenna that switch and this is the coax running from it so what I'm going to do is I'm just going to short the coax I'll short it and I'll put that across the uh the bar antenna here and we'll see what happens okay so here we go we'll zoom into this a little bit so here's the uh so put this around the bar antenna in traffic getting by and this is backed up the bridge all the ways onto the Sea Island side of things expect delays around Templeton rust Baker I'll just start tuning this see oranges and victories these workshops on the player on that well you know do you want them to understand 48 Hours something just fixed it's going to be one of those ones that get drawn out uh that you gotta remember a lot more so it's sounding pretty good am is working okay no problems there whatsoever again with the influence of a piece of shorted coax right over the end there so basically making a I don't know half turn or something like that around this so I put a few turns it would get all that much better but at any rate so that works okay so let's see what happens if we do FM I'm not expecting anything to happen yeah as you see nothing's gonna happen here so there's nothing on FM so what I'm going to do is I will get on the underside and I'll put some diodes on this and I'll show you what I've done and then we'll try it again on the underside here is this little plate and of course you know out of the entire area on this radio what I need to get to is under this plate so I desoldered this I've just stuck this on here to show you what I've done so I desoldered this and then what I did is I'll zoom on in so I isolated a few pins so I desoldered the solder here and I put some of this fibrous tubing around the pin so that it won't make contact with the tube pins so these two vacuum tube pins are completely isolated from the traces and what I've done is I've used two RF shotkey diodes and put them in place of the diodes that would normally be inside of the tube so one is actually bridged across the original diode in the tube and then this one here is the one that was you know completely in the wrong area and I should also mention I said that there was two diodes in here I should actually mention technically there is three with a common cathode so that's this replacement here so now what I need to do is uh just put this back on I think yeah that went that way so it just fits onto those two posts like so by the way the capacitor is safely discharged I checked that before I went and did this because well the capacitor's sitting right here and I wouldn't want to be sticking my fingers across that if it wasn't discharged so I'll just put this on there's enough just to have a connection here I don't even really need to solder this I'll just push this back on right now and that's tight enough just to try this out and see how this works technically I would say 90 of this printed circuit board should be reflowed the soldering needs to be fixed up it's just you know they're they're all cratering you can see little crater joints all over the place here one right there and right around the tube pins you can see that how it basically has a crack all the way around it all the vacuum tube sockets need to be resoldered and everything like that at least if I go through and uh you know do an entire restoration on this and after we see what the FM sounds like we'll make a decision should we actually do an entire restoration on this or not so I'll leave that up to you and we'll see how many of you say yes and if you more of you say yes than uh you know the majority of the comments will uh you know go ahead and do an entire restoration on that that would require recapping and tuning and all that kind of stuff too so um anyways so what I'll do now is uh let's uh hook this back up to the line again and I will I think we're good so this is in the FM position is it it is remove that around that switch is sure crusty yikes okay so hopefully that's gonna be good all right and uh I like to move the switches around a few times I'll just turn on the uh variac and uh let's power things up and see if we have any FM action yeah I like to cycle the switches this needs contact cleaning and all that too one of the things I really don't like is the way that they've done the dial string in this I'll show you that in just a moment uh this is they're really cutting costs with this radio so they they kind of went overboard in some areas and in other areas they're just completely cutting costs I hear static hear that that's just me touching the chassis I hear FM okay [Music] foreign [Applause] [Music] [Applause] [Music] foreign so FM is working so it did come to life with those two diodes and this tube so the 19 T8 is way more common than the 14 gt8 so that will definitely be left in there and of course I need to resolder all the stuff on the bottom and everything so what do you think it's alive do you think we should go through and completely restore this and make it you know bring it back to normal again or do you think we should just move on to another project this one here with me is kind of an iffy thing I'm kind of on the on the fence with it I could use this as Parts you know it's got lots of useful Parts in it you know uh this tube socket would have to be replaced that's uh that's absolutely horrible um you know the capacitors all have to be replaced at least the the non-disc type ones uh would need a complete alignment 455 kcif and 10.7 megahertz if and you know the ratio detector and I'll show you what I mean about the dial strings I'll give you the full tour here see uh you see the dial string here how they don't even have pulleys you see the dial string is just just rubbing there so I'll move this along right it has so much friction it's actually moving this clip around there's nothing moves here the this string is just rubbing that post so as you can see you know a lot of cost cutting methods no dialate right this thing has you know no dial lighting at all which is kind of odd you know they're still using you know decent components you know like you mean you know the tuning condenser and the FM tuner in here might actually have have had a license from somebody way back in the day let's see yeah right here right so that might have been in the day automatic frequency control so you know there might you can see it has a patent number on it and everything so it has AFC in there so you know they are using some things where they probably way back in the day had to pay licensing fees for and things like that Westinghouse did maybe you know so uh all in all it does work so what do you think thanks for stopping by the lab today hope you enjoyed this video if you are enjoying my videos you can let me know by giving me a big Thumbs Up And subscribe and tap that Bell symbol that way you'll be notified as soon as I post a brand new video if you're interested in taking your electronics knowledge to the next level and learning electronics in a very different and effective way and gaining access to many of my personal electronic inventions and Designs definitely check out my ongoing Electronics course on patreon I'll put the link just below the video's description under the show more Tab and I'll pin the link at the top of the comment section so if you click on the link it'll take you right there all right until next time take care bye for now

Channel: Mr Carlson's Lab

Views: 41,245

Keywords: receiver repair, radio repair, Mr Carlson's new videos, about Mr Carlson, who is Mr Carlson, testing circuits, fix a circuit, fix electronics, electronic engineering, electronic testing, restoration videos, HAM radio, CB Radio, FM radio, AM Radio, learn electronics, test equipment, tube radio repair, valve radio repair, electronic restorations, tube audio, vacuum tube audio, valve electronics

Id: JvWBXCQwhBI

Length: 37min 41sec (2261 seconds)

Published: Fri Jun 30 2023