1939 Marble Radio - Will It Work? Let's See!

hi everyone and welcome to another episode of mr carlson's lab let's get started here's an absolutely fantastic looking radio from 1939 the case looks like marbled caramel ice cream and it's in really nice condition so let's see if this old radio receiver comes to life i'm going to plug this into my current limited isolation transformer and variac supply i don't want to plug this directly into a wall because i don't know what the internal condition of this radio is so we'll see if it comes to life and if it plays that's great if it doesn't we'll go inside and we'll make it work and then in another video we're going to completely restore this radio so it should be a lot of fun so let's see if it works and if not we'll troubleshoot it so here we go i'll plug this into the supply and i'm going to turn the supply on okay so just put this like so usually there's a little lamp in the top of these let's see if it comes on ah that is a good sign right there okay so since this is a vacuum tube radio it's going to take a few moments to warm up i don't know if we can see any other tubes through this can we see anything glowing inside there not really that's very well put together very well sealed up that's making some noise if you hear that put my hand by the antenna on the back it's making some noise but very distorted let's see here it's very distorted it is trying to receive so what i'm gonna do is i'll grab my three six nine antenna look at i can just grab this hold this close to with the end shorted from the 369 antenna and it's helping this receiver out already so that's full volume and very distorted does it receive anything down here that's pretty quiet let me put this closer to here [Laughter] that's pretty quiet at the bottom end of the dial fitter so it is really really distorted so i'm wondering if that's just overloading the receive here so what i'm going to do is i'm going to take these and i will couple in that little coil that will couple into the antenna of this radio receiver and i'll be able to move this back and forth i should be able to vary the the receive here so let's see find something that's relatively strong [Music] [Music] so it sounds like it's almost overloading so that would indicate a problem possibly in the avc line and it's the volume is very very low so yeah might even be a a b plus issue like a voltage issue inside so anyways what i'm going to do is disconnect this from the power supply right now and i'm going to open this thing up take a look inside and we'll try and find the parts that are causing the issue and just replace those parts and see if we can bring this thing back to life just the way it is again we're going to end up restoring this entire radio together down the road and that won't be very far down the road i'm pretty excited about this radio it's a very nice looking radio so i'll get some tools and i'll open this thing up we'll take a look inside all right so we want to remove the chassis from this so the very first thing to do is remove the two knobs which i'm actually surprised that this one is still here because it sure came off of that tuning shaft very very easily so so usually there's screws on the bottom but in this case there isn't so these must be the screws holding it all together so what we'll do is grab a screwdriver here and very very loose all right the reason why i don't like to completely unscrew these with this is because there's a magnet in here and then it pulls the screw way up inside so loosen it off a few turns and away you go okay so that looks like the only screws let's see if this will come apart i'll just lay it on its back oh it is yeah there might be some more screws in there but no it's doing pretty good inside of the case is in very nice condition so i know these cases are pretty transparent you know light wise anyways you know obviously not to see through but you know the light shines through this very nicely i should say it looks like somebody may have sprayed some silver paint up there to stop the light from shining through i don't know if that's factory or not kind of interesting put this off to the side speaker looks to be in very nice condition so no problems there and the dial is nice little plastic that's on top is also very nice let's take a look on the upper side all the antique dust is still there this obviously hasn't been a part in a very very long time looks to be in very nice condition definitely a nice restoration candidate antenna wire up here okay so now let's take a look at the underside what's going on on the bottom this is where it gets interesting ah looks like there's a few components that have been replaced in here this right about there and zoom on in so what's surprising is there wasn't very much hum which means the filter capacitor must be working to some extent which is kind of amazing in itself so these capacitors are definitely not original so these have been replaced at some time and these are all original in here looks like it has roundies for resistors so not the squared off and allen bradley type which i would expect for something of this you know year so these are the porous body resistors that let moisture in then of course they move in value quite a bit easier so all these ones right here so it is making noise not a nice big soldering iron burn on that capacitor down there so it is making noise which is a good thing so what i'm going to do is i'm going to get a voltmeter and i'll plug the thing back in and i'm going to test some voltages in here and let's see if we can narrow this down see if we can find the issue in this radio receiver and make it work with just a bare minimum of components replaced all right let's find out why this radio receiver sounds so crackly and crunchy so what i've done is i've trimmed the little string that holds this capacitor in place so i can just move this out of the way so i can get under here to do testing if i need to so it's just one extra thing done so what i'm going to do is grab my meter here i'll hold this orange button and turn it on to dc volts that disables the power off remove this from the top put that right there so we can see that very easily then what i'm going to do is take the negative lead of my meter here i'm going to put a clip on it so i'll just clip that on right now and show you put a clip on it like this and i want to clip it to the ground of the radio so that's this lead here very easy to find because it's the negative lead off the capacitor so i'll just clip this on right here like that make sure it's not in the way of me testing anything no that's good i'm going to turn the radio receiver on now you have to let it warm up because it has tubes i also have the schematic here as well which will make things kind of easy to follow and the tube legend where the tubes actually are is right here in the case which is kind of nice so just follow that [Music] so the first thing that i want to do is just test each side of this capacitor very basic test just to make sure that the b plus is there so i'll test this one side of the cap there's 84 volts there test the other side of the cap there's 111 there so it's all there no problems with the b plus there so now the next thing i want to do is test the plate voltage of the 35l6 because it's really grungy right really grungy so it sounds like it could be an audio issue or an evc issue something like that so this is looking at the bottom of the tube socket so this is pin one and then two three four five six seven and eight so pin one two and three so pin three right here is the plate so if i look at this tube here and i go to pin three that's this pin right here make some connection here there it is so yeah there's plate voltage there and let's see if there's screen voltage there is so the screen is the next one up so that's pin one two three and four so pin four is the screen and pin three is the plate so both of them should have b plus on them so next thing i want to do is test the plate of the 12 sq7 now the 12 sq7 is this tube right on the end right here and the plate attaches to this coupling capacitor so this means that this is the plate right here and there's 56 volts on it so no problems right there so i have plate voltage on the 12 sq7 the 12 sk7 is center chassis right here and pin 8 is the plate and that would be the index there so this is pin eight no problems so there's b plus on all of the tubes and it's you know not extremely high or anything like that so let's test the cathode which is pin 8 of the 35l6 which should be this looks like they've got a piece of resistive wire here should be this one right here no problems so the cathode of this tube is working okay and the cathode directly tied to ground here and same thing over here so oh we have the cathode here goes through 100 ohm resistor it was looking like it was here but this is the cathode right here so 100 ohms and that would be this other side of where i have the ground attached 1.1 volts no problems there so that resistor's working okay and i don't need to test the 12 sa7 because it is oscillating i can hear this right just crunchy sounding so everything seems to be there very interesting so one very strange thing is when i turn it up here it's kind of crunchy there as i turn it up louder it clears up which is a very odd thing so i'm adjusting the volume control when this is happening so let's take a look around the volume control here so we have a .015 micro frag capacitor here and that is the coupling cap right that couples to the uh couples from the the wiper of this to the grid okay and that would be this capacitor right here so this is the wiper and this is coupling to the grid that looks like a 10 meg resistor there and there it is 10 meg okay so that's that coupling cap from there and then off the wiper here we have 220 picofarad which would be this capacitor right here and it looks like there's a wire off of that as well so it's a black wire which is running over to this if transformer right over here an if transformer right here so this is the if transformer the black lead off of this if transformer is supposed to attach to this end it's not supposed to attach to the wiper so you can see it's attached to the wiper the center of the vr it's supposed to attach to here you can see we have a another 220 picofarad and a 2.2 meg resistor so we have 220 picofarad or micro microfarad and then we have our 2.2 meg resistor and this is where that black lead from the transformer is supposed to attach to right to the end and they have it attached to here so it looks like a wiring error now i don't know if that's going to affect this too incredibly bad obviously it will right it shouldn't be attached to the wiper but i don't think it's going to be causing this grungy sound that we're getting so there's a chance that when this capacitor was changed maybe the person removed the wire from here and just dis disconnected it you know and attached it to the reconnected it to the wrong area over here that's a possibility or maybe even a factory wiring error yeah that's very strange so what i'm going to do is i'm going to shut the power off i'll move this out of the way turn on my soldering iron let that warm up for a second i guess i can just leave this here move this over here so what i want to do is i'm just going to remove this lead and attach it up to here so we'll see usually this doesn't look like it's really been tampered with this joint it looks pretty factory this of course has because somebody's changed this capacitor so yeah there's a good chance what i'm going to do is just grab this here and move this grab it down there heat this up move that away from there yeah everything is kind of loose here so things are just almost tacked in place so this looks like this was originally going through the hole in the eyelet here of the potentiometer and it's not now so they've moved things around it looks like just the way that this little lead is aiming you know so you can kind of tell things have moved around just a little bit so let's put that in there i'm just going to tack this into place like this and then what i'll do is move this up to the top like so just like that okay and see if that changes anything okay so here we go all right i'll just leave that there just in case we want to take some measurements i'll put that back here we go turn it back on sure the volume is down troubleshooting on the fly let's see what happens here okay it is still pretty crunchy but it does seem like the volume control is acting a little bit better so at least that issue is fixed okay so the next thing i want to do is see what's going on with the audio section here so what i'm going to do is probe this portion here with a signal tracer so i'll turn on my signal tracer and i get the leads over here so remove this hopefully my signal tracer will be loud enough for the mic to pick it up it's off to the side here okay so put the signal tracer on to here just like so make sure the volume is down that's very clean [Laughter] so it's grungy here but clean on the signal tracer off to the side here so the next thing i want to do is check the grid of the 35l6 so the grid of the 35l6 will be right over here so it'll do is i'll move this over here and turn this up again [Music] no problems so the audio's nice and clear there as well you hear how clear that is so no problems there okay so again okay so let's go to the plate okay touch the side of the plate right there [Music] [Laughter] it's very clear on the plate so this is telling me it's looking like so far let's move this out of the way it's looking like so far that it might actually be the speaker the speaker might be shot on this so let's move this over and i'll turn this the other way around very carefully this capacitor in here like so a lot of metal can so it can just sit like so so the next thing that i'm going to do here is i'll just put this across the speaker here and we'll take a listen to the speaker and see what that sounds like [Music] so it's definitely definitely the speaker the speaker's bad so what i can do is i have my other test speaker what i'm going to do is i'll grab my other test speaker and i'll just put an actual speaker right across this speaker and we'll take a listen to a different speaker and just absolutely verify that it is the voice coil all right i've got my big ugly test speaker right here off to the side see this big ugly test speaker but it works very very well so i'll remove the signal tracer just shut that off okay okay [Music] [Laughter] yeah it's definitely the speaker so i don't know if you can hear how clear that is [Music] compared to and uh so definitely the speaker the speaker is gone so i wonder if i can just move this so no no it's really toast so i don't know maybe a short in the actual voice coil itself or something like that so back with this speaker here let's just uh cruise around the dial and see if i of can [Music] maybe coupling a signal with my uh antenna here [Music] but to be honest i've been watching every single jaguars moment but i don't know that we've even released our program in terms of personnel and players and then more importantly [Music] [Music] works very well so basically one wiring error underneath and a bad speaker is really what's wrong with this radio it's humming you can hear you know the filter capacitors are definitely bad you hear it you know so it is humming you know that's to be expected that capacitor is getting warm but other than that it's uh it's pretty much it's coming to life so not bad for this little radio receiver so it's a good chance that the last tech that was in here uh did that wiring error and then of course uh who knows maybe somebody had turned this up extremely loud for a long time and and damaged the voice coil in the in the actual speaker so when it comes time to restore this radio receiver we'll go through and either disassemble the speaker and try and repair the speaker itself or i'll just find a different electromagnetic speaker and and put it in this radio receiver if you'd like to see the rebuild of a an electro magnetic speaker you can leave that in the comments below and i'll consider doing that in the restoration video for this radio as well if you're enjoying my videos you can let me know by giving me a big thumbs up and hang around there'll be many more videos like this coming in the near future we'll be taking a look at vacuum tube and solid state electronic devices alike so if you haven't subscribed now would be a good time to do that as well if you'd like to be notified as soon as i post a new video don't forget to tap that bell symbol 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 you're definitely going to want to 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 also pin the link at the top of the comments section so if you click on the link it'll take you right there alright until next time take care bye for now you

Channel: Mr Carlson's Lab

Views: 10,736

Keywords: Mr Carlson's Videos, radio restoration videos, electrical engineering, restoration videos, repair videos, test equipment repair, test electronic circuits, fix electronics, radio repair, amplifier repair, amplifier design, tube radios, tube amplifiers, valve radios, valve amplifiers, design electronic circuits, make circuits, fix circuits, test circuits, repair circuits, diagnose electronic circuits, receiver alignment, radio alignment

Id: 9t4ksE9Ogsk

Length: 27min 28sec (1648 seconds)

Published: Sun Dec 19 2021