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hello and welcome to episode 8 of don't plug it in we've uh finished up electrically restoring the triad the cabinet work will have to wait until uh some other point in time but the radio itself is up and running beautifully so we're moving on to this general electric which is an am shortwave set and when do they say this was made sometime in 44 i guess or around 1944 and this is even a little bit more bizarre than the last set this has a power supply feature that i've never seen before at least i can't recall ever seeing it we have a quote-unquote power transformer here now this looks like it has been severely overheated at some point in time from all the blistering in the tire and it actually looks like it's an afterthought on the chassis you can see how there was a actually a connector there at one point in time this radio came in several different versions for like 220 or 100 volts dc it had plug-in ballasts that went in that socket here or you could get it for the us version with what they are calling a power transformer now you would think with a power transformer we'd be working with an isolated set we are not we are working with an auto transformer which is referenced directly to the ac line this is basically a fixed version of a variac there's separate taps now the variac these taps would be adjustable for adjusting the voltage you'd have your input tap you could set it in one of two places and then you'd have an output tap like you do on the variac for changing the voltage like we use when we bring our radios up so there's absolutely no line isolation on here and just giving this thing a quick look over i can see we've got our work cut out for us obviously somebody's been in here before us this is their bare wire version of bypassing one of the bad filter caps i don't know if i can lift that out of there or not but they've stuck it down in here wrapped in electrical tape and the minus end of the capacitor is just this piece of wire that's tied to ground over here and runs across the chassis when i took this originally out of the cabinet and i left the cabinet out in the garage by the way because underneath the chassis was an asbestos uh pad that sat underneath the chassis so i've soaked the thing in lacquer and just to stabilize it but it has another problem uh a capacitor's leaked on it we'll discuss that in a minute when the lacquer's got it well stabilized i'll probably carefully lift it out of the cabinet seal it up along with the cord burner cord and take it to the transfer station where they have a hazardous waste facility this is our antenna coil now this doesn't have a loop antenna this was designed to be used with an external long wire type antenna coming out the back of the set there were two wires one had a great big alligator clip which i figured somebody was using for a ground and the other one was just like a look like a piece of speaker wire but it's two conductors but they're solid then i got here inside the set and found out that the original wire has a blocking capacitor and comes out on this cloth covered wire which is i've cut them both off but this cloth covered wire down here it comes with a terminal strip and through this capacitor to the antenna coil this other wire goes to the exact same point but it doesn't have a blocking capacitor which means this wires live at 120 volts all the time so i'm gonna have to get in here quickly and check all the windings on the coils there's an antenna coil here and on the bottom we have an oscillator coil down here there's multiple windings in fact i've blown up the schematic of the two coils you can see them there i blew up that section of the schematic so it would be easy to follow but i'm going to have to go through and check all these windings and make sure there isn't one blown open because all it would have taken is for this wire to come in contact with something grounded and the antenna coil is gone so i'm gonna be checking that out in fact i'm just gonna clip this oop uh where's my cutters oh they're over here okay i found my cutters and i'm just gonna completely remove this piece of water it has no business in here whatsoever we're just gonna get rid of it i can't imagine why somebody would do that and this is the antenna wire yeah i believe that there we're gonna have to change this capacitor of course at some point uh what oh i know what i was gonna tell you on the inside here we have get a little more light on the subject hope that helps hope that's not washing the camera out this is our across the line capacitor that looks for all the world like it came out of a 1940s automobile distributor this left a great big oily stain on that piece of asbestos that was underneath the radio and i strongly suspect it's dripping oil it's did i say it's across the line cap that is our across the line cap i suspect it might be pcb in fact i strongly suspect it's pcb which is a known carcinogen a nasty carcinogen that doesn't break down well in the environment it was outlawed totally in 1970 it used to be in powerline transformers uh metal canned capacitors it was very popular but it's got to be handled correctly so that's gonna come i'm gonna wear these i've got some gloves here and we'll we're gonna take this out immediately before we do anything back double bag that and that will go to the transfer station along with the asbestos chunks now maybe i should move the camera down here i don't know or let me see how close i can get i had mentioned when we were working on the let me lower the camera okay let's see if i can get the light right without there we go this probably isn't bad i had mentioned when we were working on the triad radio that a lot of sets had the wiring spot welded and sure enough this set does it's spot welded here spot welded over here spot welded down by the power switch which brings up our next issue this radio is absolutely directly connected to the chassis there is zero isolation not even a resistor like we had on the triad power comes in goes to this wire coming out of the switch and right here it's spot welded to the chassis as is all of the b plus circuitry it's spot welded with those wires spot welded in a dozen locations under here which means no matter what we do with the plug we're going to have a dangerously hot chassis if you were to plug in the side hot side to the chassis it's hot all the time and if you plug the neutral side to the chassis as soon as you turn the switch off you're going to have a path through the transformer through the filament string right back to the chassis so the chassis is hot all the time and i thought about what to do about that for about an hour i kept going over my head this doesn't have a double pull switch like the triad did finding a switch with this length shaft this is a special pot and a special control shaft these aren't the knobs these are heat kit knobs but this has a special knob that fits over this square section i took them easy for me to say i took them off to keep them safe because i'll never ever find a replacement if i broke one it's got a square section that fits around this and operates this remote switch as does this one up on the top there's a square sections and it operates that upper switch and then a standard bakelite knob slips over the top so just to protect those i put them with the cabinet and i've thrown a couple of heath kit knobs because i can operate these manually for the time being at any rate finding a double pole switch with that length i i don't know maybe maybe not but what i've got in mind i've got a couple of relays on order that have 120 volt windings and it's a double pole relay i think looking at the pictures there was two of them for six bucks so i bought them they look like this configuration and if they are they will actually fit in the depth of the chassis turn sideways i can actually get them in here uh when i clean up some of this stuff and get rid of some of these dead old caps i'll be able to fit a couple of these in here my thought is i'm going to use the power switch to activate the relay and then i'll use the double pole connect contacts in the relay to break both sides of the line i'll wire it up so that the neutral goes to the chassis and when the switch goes open both contacts will drop out and there'll be no connection to the chassis whatsoever it's the only way i can think of to make this thing safe um because like i say no matter which way you put the plug in the wall when the set goes off it'll be hot or when it goes on it'll be hot so i can't in good conscience pass this set on without doing something to protect that the big can electrolytic that's in there i'm not even going to bother testing it i don't know if you can see all the guts are leaking out of it and dried crusty stuff this is the stuff i'm familiar seeing in the kit when i was a kid with the big electrolytics that had a single terminal on the bottom you knew instantly they were gone because their guts have been leaking out so all the wiring in here is old rubber coated and it's literally falling apart it's just well surprised up there goes there's just pieces of it falling off everywhere so this set is going to be a bit of a challenge i'm praying that the auto transformer is in good shape uh we'll take some it's got the resistance measurements fortunately so we can take a quick look at that and find out if the transformer is in good shape in fact i could check that pretty quickly not yeah i can pull a tube out i can check this pretty quickly for excuse me resistance reading and we'll find out if that's any good but before i do that i want to get rid of this pcb capacitor i want to get that out of here entirely so that we can handle this without worrying about getting that pcb oil it is absorbed through the skin as one of the nasty features of it so i'm going to get rid of that and we'll pick up from there we have that nasty capacitor out 0.02 microfarad at 600 volts ac and it is just nasty so we're going to put that in this bag along with a piece of the power cord i cut off because that was covered in that oil i'm going to clean up under here and everything that i'm using to clean up will go in a bag second bag along with this bag and we'll dispose of that properly but that's just nasty under there okay we removed that capacitor to put down there it was a sprague 100 microfarad 250 volt that actually tested okay um but it's covered in all kinds of goo i'm just that's gone i'm getting rid of it we've cleaned up the best we can there's only so much we can do under here all of this wiring was above the level of the capacitor but the power cord went right underneath it so i cut off the whole section that was in there and discarded that as well and we'll discard that piece of asbestos that's in the bottom of the cabinet that'll all go in that bag now i guess i've got to try to figure out that looks like it might be red red and black and black and white see if they give us any colors here they do not all right we'll take some resistance readings across the line cord it says no that says 119 volt tap but 48.6 i should have this over here where you can see what i'm doing yeah we're in frame the line cord for the 125 volt tap is across the 2.9 ohm winding and the 48.65 ohm winding so uh we'll measure from here to here to see if that's any good and then this is supposed to be 35.5 ohms from here to

here that's the third winding coming out so i'll go here and here i've taken the lamp out of the circuit and i pulled the tubes out of the circuit i'm assuming these resistance readings are without the lamp and without the tubes in circuit that's my best guess anyway so let's get the ohm meter set up and see what we've got here uh 48 49.51 roughly 51 and a half to 51.6 ohms so r times 10 and my line chord goes here and that's 48 ohms there's 75 ohms and there's 48 ohms again uh where does the lamp come in those two wires there come down so all right there's the two lamp windings there and here should be about 2.9 ohms and it is it's

2.9 ohms on the money we might have gotten lucky here uh from ground to the lamp should be 48.6 i move things a little bit from ground to the first lamp winding is 48.6 so the first lamp winding times 10 there's 44 which is pretty close plus two okay from the upper lamp winding 35 ohms let's see what we've got we've got 32 ohms that's probably close enough it looks like we may have gotten lucky looks like our transformer auto transformer is okay uh next big question antenna coil i'm gonna put this on our times well i'll tell you it's ten out of work i'm just looking for continuity that's the antenna section pull up that diagram with just that component in it there it is uh where's the actual schematic ah so we've got to jump back and forth here a little bit we're gonna come in through that connection which is one on the antenna and it looks like it goes down to number six which is down here so that should have continuity down to number six and it does so they haven't blown out the antenna coil by accident we may be in luck see if there's continentally through that no no no yep there's continuity there i'm just guessing now we're contact continuity might be okay we've got continuity there so it looks like all three coils up here or four coils are intact what i'm going to have to do is i am going to just go in here this is a set i'm going to just shotgun it i'm going to go through check the resistors we're going to check uh we're going to replace the capacitors and i'll bring you back when we're ready to do a power up on this this is taking you through testing everything on this it's just checking resistors everyone knows how to do that i've got to change all the capacitors put the power cord back in and we'll keep our fingers crossed so be right back okay i had to go back and revisit the transform performer home readings it was bothering me because they were so precise i mean tenths of an hour you know 35.5 2.9

48.65 ohms they were they were pretty particular about that and it was bothering me that my readings that i was taking off the analog meter back there just weren't right so i went and got my old standby here and the winding that's supposed to be 35.5 is actually 27.8 so it's low by 7.7 ohms

the one is supposed to be 2.9 is pretty close it's 2.4 it's minus half an ohm and the winding that's supposed to be 48.6 ohms is 42 ohms about minus 6.2 all totaled up it should be 87 ohms and i've got 72 ohms and so we have a 14 and a half ohm difference and that started bothering me i said boy maybe that transformer is junk now there's a way around it we could use a resistor and series string with the heaters and i could throw a small power transformer to give me 200 volts dc not a big deal we could we could save this set even if this is gone but then i looked up here on the output transformer and this is what i did i went huh 75 ohms on a vacuum tube set output transformer that just isn't right the numbers that were going through my head were anywhere from 200 plus to maybe 800 ohms depending on the you know configuration of the output what tube it's using and whether it's push pull and yada yada so i went and i checked the traveler which also has a 50 l6 and it's got a 600 ohm primary on the transformer measures 600 ohms this one measured 338 by the way i measured the triad set it had 180 ohm primary now remember these sets are working and then i grabbed a junk box transformer that i had laying around here this is laying around in my junk box and it measures 680 ohms so this number is out in left field this 75 ohms doesn't even make sense so i'm hoping i'm hoping that these are nonsense numbers as well we'll find out when we power it up but either way we'll be able to save the set we can tap the um pilot lamp like they did here with the ballots set up we'll be able to tap that off of the 35 z6 if we have to but when we power it up we'll find out but i can hear several of you out there right now going but vern if they're all 50 l 6 or 25 l 6 outputs why the big difference in the ohms on the transformers i'm glad you asked that question we have a teaching moment here it all has to do with impedance let me get set up okay we're gonna start with a disclaimer i am in no way an audio amplifier design expert or engineer and i am no way a transformer design engineer what we're about to discuss will be in the most general of terms just so you have a basic grasp or understanding of why all of those transformers have different resistance readings and still do the same job and you have to remember those transformer not only transforms voltage it transforms impedance so anything you put on the primary or excuse me the secondary or output will affect the impedance of the primary two important concepts the first thing we need to take a quick look at is our two manual you do have a two manual don't you and we look at our 35 l6 50 l6 25 l6 whatever you've got in your radial and we come down here to where it says cathode bias which is what this radio is operating and it says our load resistance on the tube should be around 5 000 ohms that's the ideal number now it's going to vary plus or minus around that depending on design parameters but we want to see about a 5000 ohm impedance not resistance impedance loading the plate or the anode of that tube and if you want to get into the minutia get yourself the radiotron designers handbook okay this is by rca this particular edition was published in 1941 it is a wealth of information and you say 1941 that's kind of out of date no the radio was from that same period 1943. the guys who designed this

got their information out of this manual and there's probably six chapters in this book that are just dedicated to audio amplifiers and audio transformers so if you want more details i'm not the guy to ask this is the bible i'm sure you can find a copy of this either on like or somewhere on ebay keep your eyes open that's a nice book to own okay first of all is our transformer in this set any good well what we have here is an actual impedance meter you can't read impedance with an ohmmeter but you can with an impedance meter now this has limited range this is actually designed for working on like office sound systems where they have the 70 volt line and speakers everywhere but it'll take us from under 200 ohms up to about 20 000 ohms of impedance so what i'm going to do first of all is turn the thing on and we'll check to make sure that it's zeroed and it is i am going to connect onto the primary winding of the transformer audio output transformer that is in this radio and presently connected to the speaker where i'm at right now is across here with the speaker in the circuit and that's important you'll see why in a minute when i turn this on there's going to be a tone so bear with us but remember the tube manual said 5 000 ohms 4 90 ohms i'd say that's pretty close to 5 000 ohms that tells me there is absolutely nothing wrong with that audio transformer it's going to be just fine now as to why the difference well we have to understand and again this is in very basic terms transformers transform impedance so if we have a 3.5 ohm speaker and we want 5 000 ohms on the primary side that means we have a 3.5 into 5000 we have a 1 428 to 1 turns ratio in other words if there were 10 turns here there'd have to be 14 280 turns on this side there's things that factor into here that'll skew those numbers but we're just talking concepts here okay so transformer experts out there please cut me some slack if we have an 8 ohm speaker and we want 5 000 ohms that's a 625 to 1 turns ratio 10 turns on the secondary would mean 6250 on the primary so the difference in resistance between 14 000 turns and 6 000 turns is going to be significant it's going to be like half so that pretty much accommodates or covers our 180 to 680 or 180 to 340 versus 600 depending on the impedance of the speaker our turns ratio will vary and we'll have a different resistance reading for the same impedance on this side of the circuit and we can pretty much prove that i'll give you a quick demonstration here we have junk box transformer number one and i'm gonna tip down here a bit so we can see a little better and this one has a 680 ohm primary on it now i'm going to hook my meter on here and i'm going to turn the tester on and you're not going to see any indication that's an overflow because right now the impedance is way too high for this meter but i am going to put a 1 ohm speaker speaker on the secondary and let's see what happens we have 4 700 ohms on the primary okay let's call it 4700 ohms we'll go to a 2 ohm speaker we got 6 000 ohms everything in frame i hope so okay uh here's a four ohm speaker resistive equivalent now transformer doesn't care if it's inductive or resistive 10 000 ohms and if i go to an 8 ohm speaker 16 000 ohms impedance so you can see how the speaker will affect the turns ratio of the primary if we want a 5 000 ohm impedance load and this other transformer here this one has 180 ohms of impedance on these two wires this one has a tap so you can use different impedances i think this was a universal replacement transformer it's brand new it's never been in anything i acquire it in a box of junk but if we go back to our one ohm speaker i don't even oh there we go 2 000 ohms impedance different turns ratio here's our 2 2-ohm speaker 2000 ohms our 4-ohm speaker 4000 ohms now we we could use this probably in that radio close enough to 5 000 ohms if we use a 4 ohm speaker with it here's an 8 ohm and we're high now the impedance is too high it's 7 000 ohms on the primary so that is why we have vastly varying resistances on the different radios they're using different speaker impedances and different turns ratios all to end up with the equivalent of 5000 ohms on the primary and again super simplified explanation but when i look at a set like this just from years of doing it i'm expecting to see somewhere between a couple hundred ohms to maybe 800 or a thousand ohms of resistance on the primary anything in that range as far as i'm concerned is probably fine but the impedance to make the tube transfer all of its power correctly to the speaker is is what's important and this this is an ultra complex science because a 4 ohm speaker is only 4 ohms at one frequency as the frequency goes up and down the impedance of the speaker is going to sweep all over the place the amount of voltage and current through the primary is going to affect the impedance in fact you know when you pass dc through an inductor a choke or any kind of coil as you put a dc bias on it it changes the magnetic properties changes the impedance the resonance this is a deep deep art it's a black science and again if you want to go into deep detail on it pick yourself up this book right here and plan on several evenings of reading and doing lots and lots of complex math okay i think we're probably approaching the half hour mark at this point and i do have to get on with rebuilding this thing i've got a bunch of wire here of various colors i think i'm going to pull the iaf transformers out the wiring that's on them is just crusty and falling apart i don't want to have a short circuit and lose the iaf transformers all of the heater wiring has to be changed in that set so i've got hours of work to do i'm going to cut this call this the end of part a if you will and when you see this again i will have everything changed out and i won't power it up until i bring you guys back with me i'm the radio mechanic hope somebody found that information at least a little bit useful and we'll catch you on the next part of the series thanks for stopping in bye you

2021-12-08 09:26

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