Your Own Radio Station! The Knight Radio Broadcaster And Amplifier!

hi everyone and welcome to another episode of mr. Carlson's lab today we're going to take a look at a very neat collectible device known as an AM broadcaster this was made by night kit way back when and it essentially allowed you to be your own small radio station for example you could plug a record player into this device and it would transmit the music from that record player to a nearby AM radio or communications receiver now this device has some pretty heavy restrictions on it the antenna can only be so long and it can only put out so much power so that it doesn't interfere with adjacent radio stations so for example how you would tune this device is you would look for an open spot on the AM broadcast band so a nice quiet area you would tune this device to that area and then it would allow you to play your music in that little chunk of space on the AM broadcast band now you wouldn't want to try to play this on top of another radio station because it would heterodyne and make all sorts of funny noises and whistles and things like that so you had to look for the quietest spot that you could find so it is a really neat little device what we're going to do is if it doesn't work we're gonna make it work and we'll try it out we'll see how well this little AM broadcaster works so let's get started here you are sitting right next to me at the bench in the lab so let's see what we're up against first of all the night kit radio broadcaster an amplifier came in its own box the original box which is kind of neat the box itself is pretty rough condition but that's to be expected just due to the age of the device and the unit itself is in very nice condition as well this could very easily be cleaned up the paint shows signs of normal wear and tear but nothing too major I do notice though that the volume control knob does look like it's on a bit of an angle so it may have taken a hit or a drop at one time you can see that there so let's see if it moves okay and it does it feels really smooth actually so it'll probably be just fine on the top side of the chassis we can see the tube numbers and what they do so they've actually marked all this right on the top side of the chassis which is really nice so 50 c5 is a very common All American five in all Americans six radio tube these were used in many many series sets they're using one as an oscillator and one as a modulator that both the same type of vacuum tube whenever you see a tube number like this 50 c5 50 is the amount of volts it takes to light that filament up so it's a 50 volt filament si is a factory designation letter so si just allows you to differentiate this between other vacuum tubes and five means that it has five useful elements inside that vacuum tube so if we go down to a 12 ax7 very very common tube used in guitar amplifiers even today twelve means what the filament voltage it's actually twelve point six but they didn't make it a twelve point six ax seven so it's 12 ax7 they were nice to make the filaments inside this vacuum tube center-tapped as well so it's really universal this tube that's why they are still so common so you can run the tube at six point three volt filament or twelve point six volt filming ax again is a factory designation so factory designation letters right there so you can just differentiate this between other tubes and seven means that it has seven useful elements inside the vacuum tube so if you're a modern day person dealing with modern electronics a 12ax7 has two triodes inside so if you want to compare a triode to an end channel fat you can so this is technically two N channel FETs in one glass envelope kinda neat these are the inputs right here so different types of phono inputs right here magnetic and crystal this is the frequency adjustment so this is what allows the movement of this device so you can move this device to an open portion of the AM broadcast band to the quietest portion you can find just by tuning this little one control right here this is an audio transformer so this can also be used as an amplifier so say you have a record player and you don't have an amplifier you can plug your record player into this and use this as an amplifier as well just attach a speaker to these two terminals right here where it says speaker and away you go so nice little universal device to get you playing your records in short order so what I'm going to do now is turn the device upside down I'll remove these four screws right here in that should get us into the bottom here as you can see the top side of the chassis is like this and then the bottom side is like this so this is going to hold the bottom portion of the chassis on so we'll take a look inside and see what we're up against hopefully the person that assembled this these are kits so hopefully the person that assembled this didn't use a butter knife and a blowtorch like I've seen many times before let's open this up together so the first thing that I want to do is remove the tubes because I don't want to be putting the weight on these little tips right here so these are known as the evacuation point in a vacuum tube and the little chrome spot that you see in the vacuum tube is known as getter material and that's where they flash that material onto the bulb but the reason that they have this kind of a chrome looking cap in them sometimes it's on the side of the tube as well is that's a material that they put inside the tube and they flash it on to the bulb and that absorbs any impurities that leach out of the metals inside the tube over time you got to remember that these things are getting really really hot the 50 C 5 gets extremely hot it's got a really large filament in the center you can see that white little blob at the bottom there that's part of the filament in there these things get like extremely hot hot as the blazes of hell so if you ever touch something like this you'll really get a bad burn you always have to be very very careful around a tube like a 50 C 5 any type of a power tube that drives a transform or anything like that they get really really hot 12ax7 s get fairly warm nothing like these tubes right here and just over time that comes with experience you get to know which tubes are extremely warm at any rate as the tube gets hot and cold and hot and cold the metals inside they give off impurities the off-gas inside the tube and this chrome material that you see inside the tube it looks like a chrome looking material almost you know kind of mirror like inside that getter compound that's been flashed on the bulb will absorb those impurities that are let off inside this throughout the vacuum tubes life when you start to see this material go a chocolate brown color is when the vacuum tube is you know this material is getting used up let's put it that way if you ever see this material and it looks white and flaky on the inside so it's the same color as a writing here and it's really flaky sometimes you can tap the tube and it comes off that means that the tube is now at atmosphere so basically it's drawn air so there's a crack in the bulb somewhere or on the bottom portion of the bulb where the pins come out right here sometimes they crack and it's drawn air and this whole thing will just go white like a white flaky kind of cakey compound inside another question I get is is it okay to handle vacuum tubes with your fingers when they're cold yes it's absolutely fine it's just standard glass the larger power tubes are made out of Pyrex or a glass called non X Bendix the Bendix corporation that made the tubes for a pretty specific application their tubes were the majority of them were made out of a glass called non X so in order to get inside this unit what I'm going to do is remove these four screws here and hopefully the person that assembled this again these are kits person that assemble this didn't use a butter knife a roll of solder and a blowtorch believe me some of the things that I've opened up look just like that if not worse so hopefully this has been put together by somebody that took some pride in their workmanship okay the moment of truth what do you think's gonna look like in there good bad ugly here we go let's find out that's looking really nice and it's also looking all original that is very nice I do see a Jay hooked component right here somebody may have installed this in the wrong area at one time and then they used a j-hook to reconnect it I'm going to locate a schematic on this and we'll also take a look at the schematic looks like it has the original selenium rectifier in it and the capacitors holder if the capacitors are still good would be neat to be able to bring this thing up slowly on a very a canned see if the thing just actually still functions it looks like it's been put together very well so somebody did take pride in what they did and that's really nice to see oscillator coil looks really nice the capacitors around the oscillator coil yeah they look like standard capacitors standard capacitors especially this type of ceramic capacitor around an oscillator coil and an oscillator circuit equals drift in a bad way so this thing could use some np0 style capacitors in this little area right here and that would probably really improve the performance of this little unit so it would stop it from drifting around so capacitors like this just standard ceramic capacitors they really move around in temperature so when I say they move around I mean the capacitance moves around with just a minut amount of temperature if there's any movement in capacitance around this oscillator coil here this thing is going to move around on the AM broadcast band so the thing is way back when np0 style capacitors were pricey so now they can be you know had for very very reasonable prices I've got lots of them so if this thing does move around chances are I'll end up doing that so it is looking like it's in very nice condition so what I'm going to do is just quickly test these capacitors look at the diode here and if they are looking like they're okay I'm going to bring this up very slow on a current limited very akan isolation transformer and see if this thing comes to life just the way it is that would be really neat then of course if I ever wanted to use this thing down the road I would have to replace this capacitor this capacitor here and get rid of the selenium rectifier for sure those are the things that would definitely need to go the rest of the stuff there is no wax capacitors inside this thing so pretty much everything else if it's in Tolerance could be left alone theoretically now this also brings me to the safety of operating a device like this and there is quite a few things that need to be known before you start to work on something like this so first of all there is no transformer on this chassis that isolates you from the line this line cord goes directly into this unit the tubes themselves the filaments are in series most likely with some form of a dropping resistor in there somewhere and that means that in some way shape or form the chassis of this device is somehow going to be connected to this line cord that makes working on devices like this rather dangerous and you really need to know what you're doing so before you work on something like this or try to experiment with this definitely learn about what you're working on because this thing has a line voltage inside that's been rectified by selenium rectifier so it's changed to DC and then filtered and these capacitors hold a very large charge and you could get a lethal shock in something like this so definitely know what you're doing myself when I operate this thing I'm going to be using this on an isolation transformer just because again one portion of the line cord is most likely going to be somehow coupled to this chassis and as you can see we have external inputs from something else that have to run in here so if this thing is plugged in the wrong way or something is faulty on the bottom side of the chassis it could make this chassis live if this chassis is live this is extremely dangerous and that's why when I'm working on something like this I always use an isolation transformer especially with something like this because the construction is somewhat similar to an and five our all-american six radio there is no transformer to isolate you from the line and that is a very very dangerous thing so whenever you see tubes that have 50 or 25 a lot of them that say 12:35 like the 35w for things like that that usually means that the radio itself has a series set of vacuum tubes in it and that is that means that it's you know one side of the line cord is connected to the chassis in some way shape or form what I'm going to do is I'm going to get the schematic and we'll take a look at the schematic and I'll explain a little bit more about this so if you're following along and you have one of these things you're doing so at your own risk let's take a look at the schematic diagram for this night kit broadcaster and amplifier and get an idea of what the engineers were thinking of at allied radio or night kit we'll start over here with the 250 C 5 tubes so these circles here with the dots and everything inside these little dashes and everything these are the vacuum tubes themselves this is the symbol for a vacuum tube whenever you see half circles like this that indicates that a tube is split in half and as you can see v 1a and V 1 B this is one triode inside that vacuum tube and this is the other triode inside that vacuum tube so this is the 12ax7 here as you can see there's two parts one part right here and one part right here so one part right here and one part right here again if you're looking at this through modern eyes you could look at these as n-channel fat's so this would be the drain the gate and the source if you wanted to look at it like that so moving back over here again the 50c v tube was extremely common in all american v and all american six radios and that's this tube right here they also used them in some series set record players so record player amplifiers and things like that as well so this tube here is in its intended purpose it's driving an audio transformer and they're also using this as a modulator to modulate this oscillator coil so this five OC five really is not in its intended purpose it's being used as an oscillator but it is a vacuum tube and they can be used for multiple different things so this oscillator coil right here this oscillator coil right here that nice-looking red coil right there what they're doing is they're using the primary of this transformer to act as a modulator so this is a little bit like reactor or heisting modulation so the primary of the transformer here is running to the plate of this 50 C 5 and if you wanted to use this as a transformer to drive a low impedance load somewhere from 3.2 ohms to 16 ohms you would use this side of the transformer and this thing would be acting to transform impedances since we don't need to do that because we're running up you know a relatively high impedance area on this end as well what we're doing is we're just going to take a tap off of the plate here and we're gonna use this as a modulation reactor or somewhat like a heisting modulation set up and we're gonna modulate the oscillator coil so this is gonna allow us to put audio into this signal here and then that's going to be mixed and it's going to be running out the antenna connection here the coupling capacitor to stop you from connecting directly to the DC B+ here is a 100 micro micro farad capacitor now micro micro farad is old speak for Pico farad so nowadays you would just say 100 Pico farad so whenever you see micro micro just put Pico in there they also did some pretty goofy things with resistor readings way back when as well they've drawn this schematic normally which is very nice but a lot of companies they really made the resistor ratings odd they they really didn't I guess you could say put them on the schematic and rate them the way they should have and I think that was to intentionally create confusion way back when there's no other reason for writing them like that at any rate so when I come across a schematic with those goofy resistor ratings I'll definitely point that out I'll bring that out and I'm coming across this type of equipment all the time so we're definitely gonna run into those goofy resistor ratings here you know probably pretty soon here's a 470 pico farad capacitor here this one here is this capacitor right here as you can see this is 470 on it and that is not an NP zero style capacitor so it would be a good idea to replace this with an NP 0 style capacitor and then that way it would really stabilize this circuit the capacitor on this side is just to stop RF from getting into the audio section so this is acting as an RF block and of course this is going to also take away a little bit of the audio as well any time you put a capacitor it's affecting the RF and it's gonna also affect the audio what this is really acting as though is it's kind of doing a dual purpose here it's keeping RF out of the audio circuit and in the same way it's gonna actually tone down the audio a little bit you can see over here in the 12 ax7 preamplifier circuit they have a coupling capacitor between the plate of this tube and the grid of this tube and that's rated at point zero zero four seven micro farad or if you'd like forty forty seven hundred Pico farad it doesn't matter whichever way you want to look at that this capacitor here is also going to limit the audio response of this amplifier if you were to change this to say a point zero one micro farad there would be a lot more lows in this amplifier here so there'd be a lot more low frequencies as you go say towards point one micro farad that would really start to pass the lower frequencies so you can see they're really trying to trim the audio section in here and we even have a localized feedback happening within this one little circuit right here you see that from the plate back to the grid now a very easy way to remember how vacuum tubes work and how they're wired in many circuits is if you're an audio guy signal in the grid out to plate okay so the signal goes into the grid and we have amplification and we have an amplified signal on the plate the signal on the plate is out of phase with the signal on the grid and I've explained this in some of my earlier videos regarding vacuum tubes I won't go through that right now so so we'll stay for a phase inverter circuit where we're using this say we had a 33 K resistor on the plate and a 33 K resistor on the cathode and we had two capacitors running out the signal on the cathode is in phase so it's same as it is coming in and the signal on the plate is out of phase so you get your phase inverter circuit for normal amplification signal in the grid and then it's on the plate here amplified in the grid and then it's amplified on the plate we have our coupling capacitor here so I have two stages of amplification here it goes through this blocking capacitor and then into our volume control and then into the grid again and then this is the power tube this tube drives this transformer so that we can drive a speaker or modulate the oscillator over here that's how that works now as you can see there is no isolation from the line at all with this you can see that you know you can plug this cord in either way this back over here it isn't a polarized cord so you can plug it in either way as you can see AC or DC so you can see that this runs here through 33 ohm resistor through our selenium rectifier right here and then we have one filter capacitor you have another resistor here which is going to help smooth things for this area over here and also drop voltage just a little bit and then this goes directly into the circuit you can see this is this whole circuit is directly connected to this right here now you can see that they've tried to create a little bit of isolation here you can see that the B+ supply here goes through a 47 K ohm resistor and then the ground for this circuit is also you see the ground here is also connected through a 47 K ohm resistor over to this side right here so they've tried to give it a bit of isolation but again it isn't isolated at all there there is a direct connection to the AC line through here so that always has to be kept in mind for my own purposes if I was ever to put this thing into service all the time I would have an isolation transformer ahead of this thing to make it safe because there really is no way to change this design there's not enough room on this chassis to install a power transformer right that's just the way they made things way back when so we have a filter here we have a filter here so you can see the B+ is here it's filtered dropping resistor and helps us with ripple a little bit here we have another filter right here and then you can see this section is powered up off of this and then over here it runs through a 47 K ohm resistor here which is can also help with ripple and ritz Morgan also drop and over here we have another filter capacitor right here where this is connected to ground so anyway you look at it these capacitors here hold a very high voltage charge you can see hundred and fifty volts here 150 volts that's the ratings of these capacitors right and 144 at this point so this is going to charge up you know and it's gonna hold quite a charge so whenever you're working on something like this if you ever do work on something like this you need to make sure that the capacitors are safely discharged before you go into a device like this so the line cord is unplugged and everything is safely discharged if there's any problem in this circuit that actual circuit itself won't drain these capacitors off so if the capacitors don't get drained they kind of sit in there like batteries and they hold high voltage for a very long period of time and then if you go on in there and work on something without these things properly discharged you can receive a really really bad shock so these are all things that you need to keep in mind when you're working on something like this again if you don't know what you're doing and you feel uncomfortable with working on stuff like this definitely do not work on pieces of equipment like this because there is a direct connection to the AC line if you're following along you're doing so at your own risk be very very careful you can see the filaments of the vacuum tubes here are in series and so we have a 50 C 5 a 50 C 5 so we're gonna have a hundred volts here worth of filament right we have a dropping resistor here and then we have the remaining 12 volts right here twelve point six volts right here so this makes up for the residual that's left over because technically we'd only have one hundred and twelve point six volts really if these tubes were in series without this resistor right so that gives us our little bit of a softener between there and you know if you were running at say 110 right see if we're running at 110 it's close enough that it would be okay you know the current would be there enough to light the tubes a little bit reduced and if you're running at 120 you know then everything would be absolutely fine as well so they're trying to just make sure everything is safe so that you know the tubes last a long time and you know everything is a-okay with this circuit so this is one of the resistors that would be very very important to check if your vacuum tubes were all testing good and then still not lighting up this resistor would be suspect before I attach this to my current limited isolation transformer and variac supply I want to make sure that there are no gross shorts in this chassis I want to make sure that all three of these capacitors are good so there's two in this one and one down here and I also want to verify this selenium rectifier so this meter here is very tolerant of testing capacitors in circuit so I can very quickly and easily read the capacitance now this won't test for leakage or anything like that but it'll at least tell me if the capacitors are trying to do something not all meters will do this many of these meters will not read capacitors in circuit very well at all and I'll give you an example of that here in just a moment this one here is very good for that attach that there 28.7 supposed to be 20 that's reading a little high but it's there and 31.5 on the other side now here's the trick there's two capacitors in this can both the commons are tied together and run out this side so if i want to verify that i'm actually seeing these capacitors and there's not other things in this circuit tricking me i can test these in series so if i test these in series since the other one was about 28 points something in this one 31.5 I should have roughly about 15 micro farad so test them like this and look at that fifteen point one so I know I can leave this in here for testing purposes again if I'm about to restore this thing I would change this capacitor both these capacitors this one down here and I would also change out that selenium rectifier we just want to see if this thing is going to transmit this out of the way i'll Bera phi this capacitor on the bottom now put this down here like so and that connects to this point right here and it's also reading so far so good so now let's verify this selenium rectifier now the nice thing about this tester here is that it'll test diodes with a really high forward as you can see here smooth this over here and the side right here as you can see it'll test microwave diodes so diodes that are used in microwaves you can see test very very high Ford very good for testing these selenium diodes so your selenium rectifier if you'd like so what I'll do is I will attach this backwards first and we should see virtually no drop and I see no drop this is a good sign now if I see that the other direction we have problems so in this direction I should see a drop if there's drop there chances are we're good to go so here we go here we go BAM aha there's the drop so this is almost too good to be true I can test this thing without having to change any components at this point so I haven't tested all the resistors so far so good so we'll leave it at that there's no shorts or anything like that and both the capacitors are reading oh yeah I'll show you this other meter here so here's an example of a very nice meter that does not like to test capacitors in circuit this is a trap for the new guy okay so here we go look at that hat does not like testing this thing in circuit so I'll test the other one same thing so not all meters are created equal I really like this meter it's a great meter but some capacitors in circuit are kind of I don't know I'm tricky they trick the meters so this DLN 240 is a really good meter for for testing caps in circuit now when I originally got this meter years and years and years ago I purchased this because it'll test modulation reactors up to 200 Henri's that's pretty much the sole reason that I bought this thing and I just found over time that this thing is extremely tolerant at checking caps in circuit I don't think these things are made anymore I think these things are out of production no but they're a really really good meter I really like this and again that high forward for you know the rectifiers and things like that is kind of a bonus as well so when I purchased it I just thought you know I was gonna use it for modulation reactors and broadcast transmitters and things like that and down the road I found that wow I'm really glad I purchased that thing it's really a versatile meter before I go about attaching anything to this thing I want to see if this thing is going to at least even come to life so I've unraveled a cord here taking that little twist tie off so what I'm going to do is plug this into my current limited isolation transformer and variac supply down here like so I'll turn that on and I'll turn this on and I hardly see any reaction with the dim bulbs I'll just let that sit for a minute and it doesn't look like the tubes are lighting up that's not a good sign see that right there look right in the bottom right here you'd see the filaments starting to glow orange nothing's happening no that's not good all right shut this off plug this turn this thing back off again so what I want to do now is make sure that the filaments are all okay I'll just turn this on and we'll test this tube first so pins 4 & 5 are the filaments see if you look at the base of a tube so you've got pin 1 2 3 4 & 5 so I want to see if I've got any resistance between 4 & 5 here so here we go and there it is so the filaments are attached in this tube this one is good let's try this one out so pins 3 & 4 on this tube are the filaments so you've got 1 2 and then this is 3 & 4 so that's my fingers touching that well nothing there open filament so let's try this one here make sure my fingers don't touch her I get mega um readings and that one's okay 51 ohms so I've got one bad tube so I'll grab another 50 see five that's this one right here and I'll try again okay brand new tube RCA 50 c5 it would have been really nice if this original Knight tube was still alive but it's the bad one would have been nice to have at least one original tube in there okay I'll open this up brand new RCA 50 c5 okay plug that in and plug the cord back into the supply up here and let's make sure this is off to start it is turn this on and let's see what happens haha I see the lights dim bulbs lit up right there for just a moment which is a very good sign and I already see filament life here it's all of this around so you can see that the 12ax7 is lighting up and so is the brand-new tube yeah so was that one back there and everything's lighting up so that's a good sign it's what I should do right now while I'm at it is measure the B+ on the bottom side everything's good I'll put the bottom cover back on and I'll attach an antenna and we'll see if this thing is doing what it should okay here we go haha looking good lots of B+ there okay so what I'm gonna do now is put the bottom cover back on and I'll hook up some test equipment around this thing we'll see if the things transmitting kind a signal we can get out of this alright the moment of truth has arrived let's see if the night radio broadcaster comes to life and see if we get a signal out of it so I'm going to use this radio communications test set to verify that it's much better than using just a standard receiver because we can look at the performance of the modulation and see what kind of strength level we get on the screen things like that so what I'll do is I'll move the focus over to the screen and I'll explain a little bit about the monitor zoom into that a little bit so I have this receiving at 1.4 megahertz right now or 1400 AM if you prefer we want to keep an eye on the strength level here and we also want this just to go to a flatline so when we get a really strong signal with no modulation this will just go flat we can listen to it as well I have the audio turned down right now so this is off what I want to do first is give it a small antenna so I'll just put a small alligator clip on here I'll just clip that on so you can see it's a speaker and an antenna see where I've clipped that now you might be saying to yourself well doesn't this whole system need to be tuned and things like that no it doesn't the oscillator basically just runs out to this antenna through a 100 Pico farad capacitor now if this was a ham radio and say you were in the ham radio bands or something like that and this had a power amplifier tube it would need to be tuned correctly into a load since this is just coming straight off of the oscillator any random length of antenna will work that's within the guidelines so for this device there are guidelines to the length of the antenna so that is all within the rules and everything like that so this is definitely a lot shorter than those guidelines so even running this thing without an antenna would be absolutely fine there would be you know not a big deal it wouldn't hurt anything no parts would get damaged nothing like that so again keep in mind if you're gonna use one of these things there is a maximum antenna link that you can use and again that's in the rules so do not exceed that antenna length okay so what I wanted to do now is turn this little unit on and I'm gonna most likely have to tune this to 1.4 megahertz or 1400 AM I'd be pretty you know quite a fluke if it was just right on frequency so I'll turn that on right now and of course that's providing this thing is even going to put out a signal let's find out so I'll turn this up have to let all the tubes warm up these are coming into Mission pretty quick by the looks of it and what I need to do is tune this little frequency adjustment right here until I get maximum signal here and I want to see nothing there so put this on here right now and see if I can find it I don't know where this trimmer is sitting do it this way just move this out of the way so you can see the screen [Laughter] well it's getting quiet I hear attenuation relays clicking that's quite the signal three millivolts of signal so it's really close to the receive antenna so you can see the scope has gone flat and it's receiving so this is transmitting rate now now the length of the antenna and the actual antenna itself will load this circuit because technically this is just an oscillator so if I remove this right now chances are this will go off frequency let's find out you know see that it went off frequency so with no one tena I'll just put this back in here again see how I had to retune that with no antenna and this thing sitting right here and basically have 1 millivolt worth of signal is just this terminal open right next to this antenna you gotta keep in mind that this thing is receiving and it's what you know 3/4 of a foot away something like that so we can probably even test this without that antenna would be absolutely fine so what I'll do now is I'll give this some audio so I'll back this out a little bit so you can see what's going on so the signal generator here is set to 2 kilohertz with an output level of about 20 millivolts that should be fine to drive the audio so this is gonna put out audio as well so I can drive the audio into this little unit here so I'll put this it says AF generator output so that's audio frequency generator output and RCA cheater plug right here plug that in like so and clip the test terminals on here like that so now that I've done this I might need to retune this again let's just make sure because I've connected wires to this I mean about there that's good okay so I'll give this a bit of Wow look at that turn that down it's actually looking really nice look at that signal about 66% modulation Wow I'll just zoom on into that turn this down and zoom on into that right now I'm adjusting the volume control or the game control you could call it on the front and that modulates right up to the top I turn it right up that's it at tops Rado right there it's working extremely well and that looks really nice too modulation is looking really good for such a small device looking very very nice so what I'll do now is I'll attach this antenna back up to this again and retune this that's three millivolts that's a big signal attenuation relays clicking in this that was a attenuation really clicking there yeah that's looking good antenna or no antenna it looks really really good Wow I'm very impressed with this little night radio broadcaster so any of you that are gonna rebuild something like this this is the kind of results that you should get I don't honestly know if it would get much better than that so putting new capacitors inside this thing and you know swapping out that selenium rectifier could only make it better you don't have more filtering and you know we're better filtering and a better diode in there and everything like that so all in all this thing is working great absolutely great zoom back out here and put this back down to the broadcaster yeah it's working very very well so I'll just get this out of the way very impressed basically nothing done to it just a bad tube really is all this thing had in a way it went makes me wonder if the reason this thing was put back into the box or sold off is because one of the tubes went away and somebody just didn't fix it very very interesting in the last videos trivia question I asked what is this device right here and if you're just tuning it now you want to guess what this little thing is pause the video now because I'm about to give the answer this is a gas-filled photo tube so this is an s-1 response so this is designed for light operated relay applications now they use tubes like this in all sorts of different applications they use these in film projectors early film projectors and they use these things in smoke stacks or in chimneys way back when I have a pretty interesting story about that there are different variations of this tube not this particular tube but variations of it they even used little tubes like this in headlight Demming controls in some of the early cars so the number of this tube is a 921 so those have used that guest 921 and phototube got it right so now for today's trivia question this will be answered in the next video what is this thing I'm not telling you any more about it you guys can guess what this is answer in the next video thanks for stopping by the lab today I hope you enjoyed this video involving the AM broadcaster really is a neat little device if you did enjoy the video you can let me know by giving me a big thumbs up then hang around there'll be many more videos like this in the very near future we'll be taking a look at vacuum tube and solid-state electronics alike so there will be a lot of repairs restoration troubleshooting procedures and even some circuitry design on this channel so if you haven't subscribed now would be a good time to do that as well if you're interested in taking your electronics knowledge to the next level and learning electronics in a very different and effective way you're going to want to check out my ongoing electronics course and it's much more than electronics course as well I'm sharing many of my electronic designs and inventions up there as well what I'll do is I'll put the link to that under the video description so just below the video is a description and just below that is a show more written in capitals if you click on that show more tab it'll expose the link click on the link and it'll take you right there I may even pin the link at the top of the comments section as well so until next time take care bye for now you

Channel: Mr Carlson's Lab

Views: 202,120

Rating: 4.9223852 out of 5

Keywords: Learn electronics, Knight Kit, repair electronics, fix electronics, test equipment, radio repair, broadcast transmitter, Mr Carlson's Video's, understand electronics

Id: ZgxpdcIeNFk

Length: 45min 51sec (2751 seconds)

Published: Mon Apr 29 2019