Is Your Hallicrafters Trying to Kill You?

so the star Roamer and the helicrafter's s120 the Knight kit versus the s120 which was a a real favorite of people that wanted to get into the shortwave listening and maybe even the early ham radio game these were both low end receivers in the 1960s and there's a lot of them out there in the world I think you guys know about both of these receivers one thing that's interesting though is night kit takes a very interesting Approach at kit building they decided that they were always going to include a transformer in the star Roamer just for safety reasons let's get some isolation between the line and the actual chassis in the circuit whereas with the 120 a factory built receiver they knew they could get away with disposing of the Transformer and maybe having a little bit more performance and maybe uh this receiver has a little bit over the star Roamer I think some of you have more experience with this than I do but I think it's generally agreed that the s120 is a better receiver than the star Roamer at least on the surface we're not going to do a competition between these two receivers instead we're going to talk about the compromise that occurred when they decided to do an AC DC implementation with the 120. so an AC DC implementation with a non-polarized plug on the 120. and what we might do to the 120 to make it safe okay safe what's that mean hey when I turn the 120 around I see a big fat Underwriters Laboratory seal on this receiver this receiver is certified there's nothing wrong with this receiver this is not a death trap it's underwriter laboratory approved so let's look at the the power situation with the quote unquote ACDC Widowmaker receivers and see how we might treat this receiver and what is the present day General standardized procedure to put a receiver like this back in good shape and while you're at it to make sure that it's completely safe so this video is all about the AC line cord what you need to do to an AC DC type receiver to make it completely safe in the 21st century so I'm not going to actually go through the entire s120 story but in a couple of videos we're going to take an s120 that's in typical shape that's hopefully original from the early 60s and we're going to attempt to make it as safe as we can using modern techniques replacing the capacitors inside and so on so you guys of course love this old dial that was on a lot of these early receivers the fancy full station names being on here by the time that they printed this I'm sure a lot of this was obsolete already you know for instance the the old police band between 1.6 and 1.7 megahertz that dates back to the 30s 40s and 50s FM of course had taken over by the time this receiver came out people were using a VHF FM for police uh it does have some of the hand bands marked which is nice you know you have 80 meters here the aviation portions would still be um probably accurate and maybe these government or a Marine Band would still be active as shown but many of these stations along here Mom says hey what are you going to do tonight oh I'm going to be looking for India or I'd like to listen to Egypt or Iceland even better Alaska you know these were to get the uh the shortwave listener excited about International broadcast and it certainly was the height of the Cold War when these came out and the shortwave band was absolutely full of stations so looking at the back I was kind of making fun of the underwriter laboratory seal this is UL approved that means they had to do basic safety testing on this receiver and submit results to the underwriter laboratory so I would doubt that as built that this receiver could give you a shock or cause any trouble but we shall see again looking at the back it gives us a nice haco grommet a two wire lamp cord coming out 105 to 125 volts AC or DC so this is an AC DC receiver but only four tubes uses a true solid-state rectifier it does not use a 35w4 so they had to make up that lack of voltage drop by using a resistor or some type of pilot light system somehow they had to drop enough voltage to be able to use the four tubes they used which were nothing special here is the schematic and again we've got the typical All-American five tubes less one we don't have the 35w4 it has been replaced with cr1 which is a selenium rectifier so looking at this inventory approved system we can see that they're doing a lot of things right this is definitely a third generation off the line style receiver by this time they had learned to separate the ground from the actual chassis chassis ground electrical ground chassis ground electrical ground so this is uh probably a much safer receiver than any of them that came before in the 30s and 40s and by the mid 50s they were using these safety networks let's look at them here's some of the good features in this receiver in regard to safety first of all they are switching the hot lead now this is not a polarized plug so you don't know if you're actually switching neutral or you're switching the hot lead and we'll do something about that by using a polarized plug also here's where they had to make up for that loss of drop in the 35w4 they are indeed using a dropping resistor and conveniently This Is How They light the two panel lights again this all has to add up to the 120 volts between these two points and this again is an AC DC set if you used 120 volts or 100 volts DC it would light the tubes and it would operate the the radio so that's another way to handle this receiver you could actually have an external power supply that supplied 100 to 120 volts DC well filtered and you can put that into the plug if you wanted to have the ultimate in safety so the second feature it has is separating the two grounds as an internal ground and it has a chassis ground so if we look at the antenna and ground terminals over here we can see that the antenna and the ground are both essentially connected to the chassis ground not the electrical ground so that's providing some isolation and some of that isolation is uh afforded by the Transformers themselves but most of it is simply that they're they're going between the two grounds are separated by the isolation Network the third thing in this receiver that is a safety Network now this UL approved isolation Network consists of a 470k resistor and a 0.047 600 volt capacitor these are pretty good parts over here we have another capacitor the point o two two this is your uh kind of your noise filter for the line so all in all this is a very well done receiver in regard to AC and AC safety so we need to see how good is good time to fire up the receiver and see what kind of voltages we get with the plug-in the proper orientation and in the improper orientation in the socket now that we know the helicrafters s120 has the modern late 50s early 60s protection circuits in it um what can we do to try to bring it into an upgrade situation replacing the capacitors we've got the hayseed ham Fest replacement capacitor kit here these are really good quality capacitors that they're providing in this kit so I will be putting those caps and recapping the 120 using those but beyond that um we can put a nice polarized power cord this is a five footer on the radio and we could use safety capacitors for the across the line as well as the line as well as between the two grounds and in the set so these are some really nice X two capacitors and here I've got some y1 Y2 capacitors you can see the Y ones are 400 volts rated and the y2s are 250 volts rated so we will be using the y2s in place of the capacitors that have been provided by hayseed ham Fest now these are completely safe but again I'm doing this upgrade to the safety caps just to show you what the best we can do with this receiver is if you want the ultimate in safety with this receiver knowing that it does not have an isolation Transformer what are some of the things that we can do to make it as safe as possible before I do any modifications so I'm going to break a rule and I am going to bring the set up on a variac because I do want to measure what it's like right now between chassis and ground to see just how much leakage is in here would we get a shock between chassis and ground just as the receiver is here knowing that this receiver has not been touched or hopefully has not been touched since the early 60s what's the condition of the receiver right now so I am taking a chance with the receiver by powering it up without checking anything out but I'm doing it for you guys just to see what what we're going to find okay the first measurement that I'm going to make is to the cord itself with the radio turned off I'm going to measure from each side of the plug to ground it's open on that side let's open on that side okay not getting anything plug is totally open both sides let's turn the radio around put on the Ground Terminal okay I've got 530 K to the Ground Terminal on that plug on that uh and on the other side it's open so this is the this is the ground side right here next we're going to turn the set on again we're going to make a measurement to the front that's open that's open and now we're going to go to the ground blade again the 538k remember it's a 470k to ground so that resistor is going up in value and now the other side also 538k 540k okay so both sides are now showing the safety resistor to ground I would not expect that there would be a problem with this radio the capacitor is not shorted out completely all we're reading is the resistance of the safety resistor it's a 470k resistor it's gone up to about 540 550k okay next I'm going to turn the radio on make sure it's on volume on full and we're going to slowly bring the variac up I am working through an isolation Transformer bringing it up slow this receiver has a selenium rectifier power supply it does not need to have a tube warm up to begin to produce B plus bringing it up about 40 percent of the voltage I'm starting to see a dial light starting to hear some noise now I'm about 80 percent continuing to bring it up 90. full line voltage while they're traveling in construction zones workers say that jobs are more dangerous these days because people are often distracted first few months of this year there are okay I think it's working properly it's tuning pretty hard here but that's okay we'll fix that [Music] okay next thing we're going to do is we're going to get rid of the variac and the isolation Transformer we're going to plug it right into the line we'll verify the line is proper and we'll measure again from ground and Chassis on the radio to a good ground and see if we can get any voltage across there so I have a very fancy Outlet strip from Staples this guy actually has two green lights on it right now one of them says grounded and the other says protected they're both green that tells me I have a good Outlet here so if I was to go between my station ground which is all my equipment grounds and the ground on this Outlet strip I would expect to see very low voltage and I do it's like 0.03 volts ac between these two grounds this is the power ground this is my station ground now if I was to put this into the neutral of this Outlet strip I would expect it also to be low and if I put it into the hot I would expect 120 volts okay so this is all proper everything is good here we have a good strip we know where ground is we know neutral is grounded and we know our station is grounded okay I've just plugged the receiver in I have no idea what's ground and what's not on the plug I've just randomly plugged it in I'm going to turn it on see how long it takes for it to warm up the lights are on the radio is warming up okay [Applause] [Laughter] so I've got about a volt to the outside chassis from my station ground one volt now let's go to ground I have 0.2 volts ac to the Ground Post and point two to the antenna post and point two to this screw so all is good I am now going to unplug the radio plug it in the other way okay I've now plugged in the radio the other way to the screw 2.9 volts to ground 122 volts to the antenna 120 volts okay 120 volts to the station ground to the Ground Post now the question is how much current how much current between those two points I now have the plug plugged in the wrong way and we're showing voltage we definitely would get a shock let's take a look at the chassis 98 volts to the outer case 122 volts the full line to ground to my station ground are we going to get a tickle yeah we're going to get a tickle okay I have inserted a 10K resistor On The Ground Terminal of the radio and we're going to connect the ground wire to this resistor to see how much current would be drawn through a 10K resistor looks like three milliamps three milliamps through a 10K resistor now let's just prove we're okay by switching the plug back the other way measuring this again nothing okay nothing from ground to ground so let's go back just verify this again 3.1 milliamps now how much voltage is across that resistor how much voltage across the resistor so we're going to connect directly to the resistor we should hear the hum come back and now we're going to measure across the resistor there we go 30 volts ac 30 volts ac across the resistor foreign let's double check the current 30 volts ac across a 10K resistor at 3 milliamps AC would that be enough to give you a tickle is the question so we're measuring 121 volts but once we put a 10K resistor between the two grounds it goes down to 30 volts and we know it's only 3 milliamps would we feel that would we feel that that's the question would we get a tickle so helicrafters has some minor insulation between the actual outer case and the chassis I would want to depend on it I mean when we put our meter on there it's 96 volts ac so it is less than going directly to ground okay but you have to consider that the case is basically connected to the Ground Post on the radio they did put a fiberboard protection on the back trying to keep you away from the chassis even more but the question is am I going to feel a tickle between the chassis of the radio and my station ground that's what we want to know of course I'm going to do it come on guys you know I'm going to do it so I'm only going to do it with one hand but I am going to do it okay I'm going to feel between the clip lead and the outside of the resistor see if I feel something oh they do when I just touch it I feel it it's just a little tickle though you guys are all familiar with that right it's just a little tickle but that's 120 volts ac it's just at such a low current that my body's impedance is preventing an issue so next let's try it without the resistor in line directly from the ground post to this again just a tickle and Chassis chassis to the alligator clip again just a tickle so even though this thing is from the early 60s and there's definitely voltage there I can measure there's enough protection in that circuit that I'm just feeling a little tickle okay so that's that's our starting point that's where we're beginning with this receiver before we make it safe

Channel: MIKROWAVE1

Views: 17,551

Keywords: Hallicrafters, WU2D, Mikrowave1, AC/DC Radio, Off the Line Receiver. Polarized Plug, Radio safety, High Voltage

Id: KxFe94kIKR8

Length: 25min 37sec (1537 seconds)

Published: Sat Aug 05 2023