DIY Test Gear: Dim Bulb Limiter / Tester with Isolation - Design and Build

[@waltwimer2551]

Nice idea / design! And while I knew immediately what the schematic would look like (being a seasoned EE myself and having designed/built similar projects), your whiteboard presentation was excellent! Rather than just showing the final schematic right off the bat, you drew it step by step, perfectly illustrating the evolution of your thinking as you designed your project. That's a great way to help teach newcomers to electronics. Bravo!

[@electronicsoldandnew]

Thank you.

[@patrickbouldinkm5l143]

I have to agree with Walt, just simply an outstanding teaching method, wow. As you guys say, "brilliant!" Thank you.

[@electronicsoldandnew]

Thanks

[@midmodaudio6576]

I must have watched at least a dozen videos about "dim bulb testers", your design is by far the most sensible and is also presented with the most clarity

[@electronicsoldandnew]

Thanks

[@FunnyBunnyShowNYC]

Beautiful. I have an idea. Could you use a relay, so that the bypass automatically turns off when you turn the main switch off. This way, you never forget to turn off the bypass switch. So, the bypass switch would actually be a momentary push button to turn the relay ON. Then, when you turn the main switch OFF, the relay automatically turns OFF.

[@electronicsoldandnew]

That’s a very good idea. I’ve actually forgotten it in bypass once, but once can be once too many 😊

[@noelconway2589]

@@electronicsoldandnew experience has thought me to omit the bypass switch altogether. While I have been lucky and not destroyed anything, I have forgotten to reset it more than once. If I need to plug the DUT onto the mains I just do it !! Not everyone's solution, but it works for me !!

[@electronicsoldandnew]

👍

[@andrew_koala2974]

when the main switch is turned OFF Note that the word YOU refers to some'one' specific The word one refers to any 'one' soul (as opposed to a some'body' which is a DEAD entity Also learn that ON / OFF and on / off are used in different contexts ON / OFF is uses when referring to SWITCHING such as turn the light ON on/ off is used in the context such as : I start work in Monday and I am off on the week-end Clearly you were never taught correct and high-level English How the word ON came into being is an lesson in ancient history that is outside the scope of this comment - and would involve lengthy history lesson Nevertheless now you are expected to know the difference in usage even though it is clearly written on switches ON OFF and you failed to pay attention to detail. So learn to pay attention to detail. Make sure you actually see what it is you are L00KING at. As your eyes see one thing and your brain sees something entirely different. Understand that ZOMBIEs have eyes but cannot see - ears and cannot hear You were programmed that way - bu your corrupt CORPORATE GOVERNMENT indoctrination system - The School was for indoctrination - not for learning

[@cookcrazy]

LOL - I am building one with a relay from this guy's video - he has a schematic on his own website - a few details missing, but it seems easy enough to follow. kzbin.info/www/bejne/h5S3lJ5oa7SFabcsi=WpAWCbuga94xNiAu&t=82 This video by @electronicsoldandnew is much better at explaining the schematic and details, though... Man ya gotta love KZbin LOL🥰

[@randygk8856]

Thanks for the instructions and video. I just built mine with a place for my variac and will plug into a separate isolation transformer. Thanks again

[@electronicsoldandnew]

my pleasure

[@bbleckert]

I found this excellent video yesterday. Went straight to the garage and duplicated your solution using a box made of wood and old parts that I have collected over the years. Not as fancy as yours but still the same function with four bulbs and a bypass for the limited current and it works well!

[@electronicsoldandnew]

👍

[@RI-ns8wz]

REALLY USEFUL!!! Iwas searching a dim/limiter/isolator "with a twist" and I found It here! THANKS A LOT! (I am from Argentina)

[@electronicsoldandnew]

Pleasure 👍

[@hestheMaster]

Looks a lot safer than the one Mr. Carlson did some years ago. Love the digital readout display! The bulbs look like lottery balls! Very cool build!

[@electronicsoldandnew]

Thanks. These lamps are getting hard to finds, unfortunately.

[@zorka4098]

Thanks for this detailed explanation. I always liked how you did this previously and so I built one (like the original) as best as I could based on how I understood you used it. However, mine may be more complicated than was needed. I also like having the isolation transformer right there as you have done.

[@electronicsoldandnew]

Yes. The isolation transformer is very handy.

[@perrymattes4285]

Very nice little piece of test equipment. I don’t usually work with voltages this high but nice to tuck away in the memory banks for just in case.

[@electronicsoldandnew]

👍

[@ThePapa41]

Very nice presentation, you do nice work! Louis S.

[@tomluque]

Lovely layout. I would suggest flipping the orientation of the ON/OFF power switch because it is much easier to slap the switch down for OFF during a panic shutdown. Just like your wall light switch in your home (I'm in USA).

[@electronicsoldandnew]

I grew up with the opposite conversion so I always do it this way 😊

[@eldontyrellcorp]

I just finished building the same dim bulb tester with the addition of a standard "resettable fuse" (1A) which is mounted on a rail. I can easily swap if for another module if necessary. I had an isolation transformer lying around and I even have a bigger one that I had paid 3€ on a flea market. This really is heavy ! The small one should be enough to use with tube radios.

[@electronicsoldandnew]

Yes, the current drawn is quite low.

[@mikeoliver3254]

Nice design I just started thinking about building a dim bulb tester, you have inspired me to build a nicer unit that integrates a few extras.

[@electronicsoldandnew]

You won’t regret it. Mine is extremely useful.

[@Jonathan_Doe_]

If you want something mostly ready made enclosure wise…. 6 or 8 unit rack case for audio equipment would fit the bill. Can buy blank front and rear panels for them too, and handy drawers (if you have space left over). Or follow MendItMarks approach and use household switches/bulb holders/sockets mounted on a board quite far up the wall next to the bench.

[@richardgoebel226]

That is excellent! I have an Isolation transformer, small variac and ammeter that take up way too much space plus the cables for all of them. Looks like a good project for this weekend. Thank you for sharing.

[@electronicsoldandnew]

richard goebel : enjoy.

[@cpilg1070]

Very nice, think I'll build it. Except I'll make the bypass turn a red ( maybe flashing light ) on when it's in bypass mode and maybe a green light for safe. That way I don't have to worry about the exclamation mark... 😎

[@electronicsoldandnew]

Blinking beats exclamation any day :)

[@GeorgeWMays]

Excellent. Thanks for taking the time to put this together.

[@electronicsoldandnew]

George Mays : You’re welcome.

[@jazzncofee3871]

👍 great contents! I learned it and tried ans succeed to build my own tester based on learning from you! Thank you!!! I'm happy to connect with you for same hobby!

[@electronicsoldandnew]

Glad to know it proved useful to you.

[@anthonyvee]

Very neatly done too!

[@electronicsoldandnew]

Thank you! 😊

[@waynethompson8416]

Manufacturer and Part Number for the lighted switches, please! As always you make things easy to understand and point out vital "Need To Know" information.

[@electronicsoldandnew]

I’m afraid those were bought years ago, so I don’t have it. There was some discussion in the comments where others discussed possible options. Hope that helps.

[@vladimirpetrovic1316]

Nice... I simply have a variac with two light sockets... this is on steroids. As you said deluxe version. Well done

[@electronicsoldandnew]

Thanks.

[@gregkrobinson]

You can also use halogen lightbulbs instead of tungsten, and they work even better as their current coefficient of resistance is higher, meaning the resistance of their filaments is lower when cold, so deliver more power when there is no fault, but "trip" just as well as tungsten if there's a problem. My version has 8 100W bulbs, but I work on a lot of musical instrument amps, so need that sort of power.

[@electronicsoldandnew]

Greg Robinson : very interesting. Haven’t tried them.

[@kolinevans9127]

Thanks for the comment I couldn’t find ‘normal’ filament bulbs so I took a hedge on some 40 and 100w halogen then did a little research and it would seem they would function.

[@kolinevans9127]

Electronics Old and New by M Caldeira Greg seems to have used halogen? Considering their ‘coefficient of resistance ‘ I can’t see why they wouldn’t work great, that’s why I purchased some at the dollar store

[@silasfatchett7380]

You can use halogen bulbs, but if you live in the EU, get them quick while stocks last, because the interfering idiots in Brussels have banned them.

[@DjAnth0n1]

Excellent work as always M Caldeira,thanks a lot for sharing.

[@electronicsoldandnew]

You’re welcome.

[@johnc.4625]

When I add the meter, it works fine but I have issues with my dim bulb at that time. Either it does not limit or I can’t turn mains off. I’m guessing it’s where I’m inserting this. Any suggestions? Thank you

[@electronicsoldandnew]

It could be the type of switch you’re using. Check the comments in this video. I believe it has been mentioned

[@electrolatif]

In bypass you can make it Auto using relais. Any time you one your bulb tester will be use limit(can use green light like indicator).... Today i learn some new things From you, you get new subsrib ❤

[@electronicsoldandnew]

Thanks

[@grahamluscombememories9897]

Thank you for this video. I have a question about the voltmeter / ammeter. The eBay listing is no longer available to purchase this. I am building a dim bulb tester that will work in conjunction with an external variac and external isolation transformer. Since my voltage can vary with the Variac from 0-120V (i’m in the US), I need an ammeter that will work with lower voltages. Most of the ones I see on line only work between 80-300V.

[@electronicsoldandnew]

I believe that’s the norm, unless you get one that requires a separate low voltage DC supply

[@anthonyvee]

Great design!

[@electronicsoldandnew]

Thank you!

[@GeorgeWMays]

Great video. Great project. It's appreciated. Thanks a lot.

[@electronicsoldandnew]

pleasure

[@ricardoaliasdelatorre6836]

Manuel in your dim bulb tester design, didn't include a variac transformer in order to control the voltage has to be applied to the radio. Do you have any reason?

[@electronicsoldandnew]

I didn’t have a variac at that stage. Got one later and now use the two in series.

[@jameslangdon10]

With incandescent bulbs being banned now in favour of LED bulbs, what optical device would you use in place of the bulbs ..... ?

[@Jonathan_Doe_]

One thing to note is… High power Push Pull guitar/bass amps (50 watts and upwards) will still make a 150W bulb glow faintly after warm up, even with no shorts, and you’ll have to recheck the bias once you run it without the limiter.

[@electronicsoldandnew]

👍

[@sajjadatd]

although the circuit is very simple, but I love the idea, thanks a lot to share such a idea ...

[@electronicsoldandnew]

Sajjad Bahadar : my pleasure.

[@Marwatt]

hello... great video explained well like all the others... just one (maybe stupid) question: if the intention of using the lamps is only to reduce the current when there is a short circuit (and therefore highlight the short circuit when the lamp lights up) wouldn't it be enough to put only one 40W lamp instead of 4? I understand that a single lamp also limits the voltage across the load... but we only have to see if there's a short... right? or is there another explanation for having much more lamps? thanks in advance and keep up with these interesting videos.

[@electronicsoldandnew]

The detection of a short circuit is only one part of the story. You can get breakdown of components as they are subjected to high voltages that may not happen instantaneously. It may actually take some time before a short occurs, and in the meantime you want to see if the radio has any life in it. Also, by checking how much current it draws you can get an indication of the state of the device.

[@Marwatt]

@@electronicsoldandnew ah... OK. I got it. thank you

[@jerkerfridh8189]

Excellent work! I've allways liked the sound and beauty of old radios and having watched your videos for half a year now I feel ready to have a go at my collection. B.t.w. where did you pick up your english? Cheers!

[@electronicsoldandnew]

Jerker Fridh : have fun. My English was my first language when I grew up in South Africa. Studied there then left after university. Now living in Madeira.

[@robnic52]

Apologies, you said the light bulb is in series with the radio (dut) but then said the extra bulbs are added in parallel to that single bulb exactly as per your schematic. So I need to listen more carefully. 🙄👍Thanks, great, informative video. I also liked one by fibbers workbench where he measured the resistance of a cold 75w bulb using a meter. Ohm's law showed the bulb would draw about 8 amps but measuring the ampage with the bulb on mains power it drew a few milliamps. Tungsten filllaments cold are very low resistance. Hot (in use) the resistance increases dramatically. I guess this explains why Tungsten bulbs shine fully bright almost instantly, whereas an electric heating element can take a relatively long time to warm and glow?

[@electronicsoldandnew]

👍

[@jameskrivitsky9715]

Great build Mike, I watched a setup on Mr. Carlson's Lab in which he used a different transformer and schematic, and I'm liking both designs. I would make one minor change when I build mine.... I would have the "ON" switch flipped over. This way when the unit is turned completely off, you would start out with the "ON" button in the down position (like a wall switch ) and the LIMIT button in the up position. Thus, when it is powered up, both ON and LIMIT would match ( being in the up position ). If you wanted to bypass, you would need to flip it down away from LIMIT. I enjoyed your video, a great learning DIY tool. Thanks J K

[@electronicsoldandnew]

James Krivitsky : I made some modifications recently and published the video on those. You may also want to see it. It was posted a couple of weeks ago.

[@andrew_koala2974]

Here is Mr Carlson's version kzbin.info/www/bejne/a2LQm6dvo6uim6M

[@brucedowd2501]

Thankyou - I am process of building this project ! Ever thought of adding a Variac feature to project .

[@electronicsoldandnew]

Bruce Dowd: I did, but it would become too bulky for my work space.

[@aslerunarborgersen5175]

I liked this build very much, I have a current limiter already but liked your idea very much. What kind of switches did you use?

[@electronicsoldandnew]

They are neon rocker switches, but seem to be special as they don’t light up in reverse. Someone brought this issue up in the comments and you can read it to get a better idea.

[@windward2818]

Possible improvements: The design of an isolated adjustable AC power supply for repair and testing (calibration) is largely dependent on the type of product that will be repaired or calibrated. This is why you see so many different overall approaches on youtube. So if the target product is a tube radio then the design takes shape around what works best for radios, with one appoach shown in the video. If the AC power supply is to be used as general purpose supply across many products for repair and calibration (high and low line) then the design becomes more complex and usually more expensive. The obvious addition would be a variac after the isolation transformer to adjust line voltage. Also common, in my experience, is to replace the bulbs with non-inductive power resistors and include an analog AC ammeter. The power resistors eliminate the changing resistance of a bulb from cold to hot (which introduces a current dynamic that is not from the Device Under Test) and the AC Ammeter analog movement visually is much slower than a digital meter and by its behavior you can tell a lot about the fault, especially if you repair the same product types or models. Failure root cause for specific models over time tend to follow a pattern, which many times, in the end, reveals weakness in design or unforeseen limitations of the electrical components used. If you repair the same model type device (or family of similar devices) you can tell a lot about the failure by visually observing the analog meter movement when powering the device.

[@electronicsoldandnew]

👍

[@BjornBlomstrand]

Thanks for the ideas and the wiring diagram. Have made a list of al the parts. And also a question. We do have the same voltage 230 v in Sweden as you have The insolation transformer will be a must. Will the rotary transformer do the same insolation as the full insolation transformer? Regards Bjorn

[@electronicsoldandnew]

No, the variac is NOT an isolation transformer. Be careful, as there is a lot of confusion about this on the web.

[@BjornBlomstrand]

@@electronicsoldandnew Thanks for answer. I had my suspicions! Bjorn

[@robnic52]

Hi, early in the explanation I believe you mentioned that the bulbs would need to be wired in series but your schematic seems to show them wired in parallel. Which seems correct? Won't this decrease the overall resistance as you add bulbs? A 200w bulb would have a thicker filament (and lower resistance so higher current flow) than a 100w bulb. I find it confusing, sorry.

[@electronicsoldandnew]

The bulb is wired in series with the load. Then you can reduce the restriction by wiring more bulbs in parallel with the first bulb, effectively allowing more current to pass.

[@brucedowd2501]

One other question when you say 350 watt transformer , what is that in VA - One I am looking to purchase for this project from Element 14 is 25 VA . Power Factor is in there somewhere . Cheers

[@atschirner]

very nice project and detailed review. Have you thought about using the unused side of your bypass switch to extinguish the lamp switch indicators?

[@electronicsoldandnew]

atschirner : I could but that would require a ‘Break’ on activating the switch, and I don’t want to get into inverting signals which I could do with a simple relay.

[@atschirner]

Or the alternate action of a DPDT switch?@@electronicsoldandnew

[@johnmcgiv1]

This is another excellent explanation and video so precise very well done. I have a question please Mr Caldeira. Will the lamp limiter work on an oscilloscope power supply with over/under voltage and temp protection. My Fluke 3092 turns on shows display and text squeals then shuts down after about 4seconds I cannot take any voltage readings just an old novice, many thanks again for your video, I made a 3x60w unstitched limiter after watching this video previously several times actually haha.

[@electronicsoldandnew]

The scope will draw very little current, I expect, so the limiter will be practically “invisible” to it unless there is a short circuit.

[@johnmcgiv1]

@@electronicsoldandnew Many thanks for replying.

[@Bluelagoonstudios]

Hi, very interesting video, I have already a selfmade variac, with isolation transformer build in, and analog meters for current and voltage, so if I understand, I just have to build only the lamps with the switches? Just asking, thanks.

[@electronicsoldandnew]

I have two videos on my channel that describes the unit you’re referring to. Have a look at that as it may help you.

[@Bluelagoonstudios]

@@electronicsoldandnew ok,thank you very much :) greetings from Belgium

[@RixtronixLAB]

Nice info, thanks for sharing :)

[@electronicsoldandnew]

pleasure

[@jeffv.akaonsjeffke9865]

Im building one at this moment. The doubt I have, is why did you put a switch on the first bulb, as you will always have it in series with the load. Besides we have the bypass switch in case we want full current flow. Am I missing something?

[@electronicsoldandnew]

Having all the bulbs switchable gives me all the alternatives possible. What if you actually wanted just 60 W? If the first bulb was permanently on (40 W), you would not be able to achieve this.

[@jeffv.akaonsjeffke9865]

@@electronicsoldandnew ok, thanks. Mine will have 4 times 40w bulbs (what I could get my hands on with a real filament), so the next step up from 40 will be 80w. So only 3 switches in my build then. Thanks for the video, never new about these dim bulb limiters. Next will be getting an Iso.Trans. Got a real heavy shock ones grabbing with both hands an old radio chasis plugged in the 220v. My hart made an arritmic pulse and luckly I bounced backwards in the sofa letting the chassis loose. The shock was way more powerfull than a 220 v ac tickle. After that I got a bit scared of old radios in bad electric conditions. Did build myself 2 guitar valve amps.

[@electronicsoldandnew]

Yes, the shocks on those is normally DC volts, which is worse 😊

[@jerkerfridh8189]

That explains it,well if you'd ever come across a radio of swedish origin,AGA,Luxor etc. I'd be happy to assist in swedish. Cheers!

[@electronicsoldandnew]

Jerker Fridh : thanks for the offer

[@captaintube2696]

Inspired by your video, I have finally built my own DBT. Since I don't have an isolation transformer, I added an MCB followed by an RCD at the start of the circuit, before the switches - just for added safety. I have a question around the voltage - if I test a load with let's say a 40w bulb, I'm assuming that the bulb not only limits the current but also the voltage since they're typically 2 resistors in series. 1. Is my understanding correct? 2. And if this is true, how can we calculate the voltage available to the load depending on the number of bulbs being switched on in the parallel circuits? 3. Lastly, if a device needs a minimum of 220v to operate, I'm assuming it can't be checked using this tester? Sorry for the excessive questions.

[@electronicsoldandnew]

The voltage drops after the current starts to flow, so actually it cannot be relied on to drop voltage. You cannot calculate the voltage that results accurately, because it always depends on the current drop across the load, which you don’t really know until you try it. You can test it because the device usually starts operating at far lower than the rated voltage .

[@captaintube2696]

@@electronicsoldandnew Thanks for the info. Another strange event - I connected a device with 110-220v and 40w rating to the load. I tried with a 40w bulb, but the load did not power up. I then added a 60w bulb in parallel but the load still did not turn on. The load was a hot glue gun. Any idea why this would load would not power up with a total of 100w globes connected?

[@electronicsoldandnew]

No idea. Perhaps the hot glue gun requires too much current and the bulbs reduce it too much.

[@captaintube2696]

@@electronicsoldandnew I'm guessing that's an incorrect rating mentioned on the gun. Will try with a 200w bulb or higher.

[@teslakovalaborator]

Good work !

[@Retro.Studio]

Nice video! One Question left for me; what about appearance "forced grounding" using a older 2-core lead cord, is that safe when this current limiter is build with a 3 core cord? Or can we easily switch out grounding with a on/off switch? Thanks

[@electronicsoldandnew]

Retro4fun : if you plug in a two-wire plug you just automatically cut ou the earth, so no switch is necessary.

[@richardshort4587]

May I ask a question please. If the secondary output has no neutral but basically Line 1 and Line 2 output. Does it make a difference which side feeds the dim bulbs.

[@electronicsoldandnew]

no, it doesn’t.

[@richardshort4587]

@@electronicsoldandnew Thank you for you’re quick reply. Great videos by the way. 👍

[@kolinevans9127]

Great design my only suggestion is make the bypass a momentary switch?

[@electronicsoldandnew]

Kolin Evans : Could do, but I want the isolation transformer to work continually after the initial testing or shorts, therefore to fixed switch.

[@mikeyaudio167]

thanks very clear exemplend video :)

[@daveturner5305]

I'm finally getting round to building an isolated dim bulb tester. Tungsten or halogen bulbs are not the problem for me. Where I need advice is how to source a suitable toroidal isolation transformer. I'm UK based so 230/240V would be ideal. Do you have any suggestions?

[@electronicsoldandnew]

Try RS components or Mouser.

[@daveturner5305]

@@electronicsoldandnewI must be asking the wrong questions because I can't find a 230/240V 1 to 1 toroidal. Ho hum I'll just have to keep looking.

[@electronicsoldandnew]

look for 2x115vac primaries, and 2x115vac secondaries. Use them in series

[@daveturner5305]

@@electronicsoldandnew Thanks. Finally found one at RS Components.

[@electronicsoldandnew]

👍

[@marknijssen9224]

I build this about the same way. but i have a problem with the neonlights in the switches, when i switch one of them on, all the neon lights go on, they get there power of the common of the bulbs via the bulb that is not powered on

[@electronicsoldandnew]

Check the comments on the video. Someone mentioned which neons work and which don’t. I just used some I had on hand and was lucky.

[@ErwinSerle]

How will the bulb be when decent ?

[@electronicsoldandnew]

Not sure I understand the question.

[@ErwinSerle]

@@electronicsoldandnew see your pop up text early in the video : incandecent bulb ...

[@rogerstephenson5639]

I am currently building a dim bulb tester using 4 bulbs in series and with 4 switches to bypass each bulb as needed. Is there any advantage to your parallel build or any reason not to use a series configuration?

[@electronicsoldandnew]

Roger Stephenson : parallel configuration let’s you add wattage to reduce the limiting, while always having the lamps subjected to their maximum voltage in the event of a short, so they will light up visibly. In series, you will probably not see any bright glow in the event of a short because the voltage across each lamp is divided by the series chain. I’d go with parallel.

[@rogerstephenson5639]

@@electronicsoldandnew Thank you and I will indeed follow your example. It is a nice tidy arrangement as well. I was viewing it as being a poor man's variac as well as a dim bulb tester.

[@mountainhawk9802]

great video...thanks

[@sanjursan]

Nice design, but at 3:05 you say that the first 60 and 40 watt bulbs are in parallel, and thereafter it seems everything is in series. What gives?

[@electronicsoldandnew]

Think about it: a bulb is in series with a load. Add another bulb in parallel with the first bulb, you get two bulbs in parallel. Then those two are in series with the load.

[@borayurt66]

Exactly what I had in mind for sometime now. I had a 1KW isolation transformer (220v in - 240v out) wound for me by a local transformer manufacturer and bought four 60w incandescent bulbs in blackmarket (not sold legally anymore). Your deluxe version is fine, but then mine will be the ultra-delux version :-) since I am also planning to include a 1.2KW variac I salvaged a few years ago from a junk yard which is almost brand new. I have the gauges, lights, circuit breakers all ready but need to convince my lazy ass to get up and built a strong box to contain all this now... Would you recommend putting the transformer or the variac first? I am planning to put the transformer first to make the whole thing isolated from mains but I would like to hear your opinion on this too. Thanks for the great video, this may give me the push I need to finally put all of these together and make something useful...

[@electronicsoldandnew]

Bora Yurtoren : I think I’d also put the transformer first: switch, 4A fuse, transformer, variac, dim bulb setup, voltage and current measurements, output. Don’t let the mains earth anywhere past the transformer. Definitely a super-deluxe version.

[@borayurt66]

Making the box out of MDF is not a bad idea at all, much easier to work with compared to aluminum frame and panels I had in mind... But in my case, 1KW transformer and 1.2KW variac, plus the MDF, it will be the military definition of "portable"; Anything that you do not need a forklift to move... :-) Greetings from Turkey!

[@EwaldBurger]

Bora Yurtoren Hello, be aware that when using such a huge transformer you get serious inrush current that may trip your mains circuit breaker. You might end up to have to use some inrush current limiting when switching on. Maybe another light bulb in series with the idolation transformer and a time relais that switches on a second later and bypasses that light bulb then. Enjoy the build!

[@borayurt66]

@@EwaldBurger Thank you very much, this is really something to consider.

[@andrew_koala2974]

One of the more stupid decisions equally stupid politicians made is to make Tungsten Filament bulbs illegal -- Though they can be found with some persistent searching. There is also a company in the US of A that sells a huge variety of light-bulbs of every description.

[@geoffpickles9064]

Hello Miguel, great video and like your capacitor tester i have to build one! can you tell me a bit more info on the type/make of module you used? thank's Geoff

[@electronicsoldandnew]

This is the module used: rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F201561488389

[@geoffpickles9064]

Thank's Manuel! bye the way,are you going to repair/service any valve guitar amps in the future?

[@electronicsoldandnew]

I’ve designed a built a couple, and repaired lots. I have not done a video on these as there are guys out there doing superb videos ... Guitarlogist is the first one that comes to mind, probably a lot better that any I could do.

[@geoffpickles9064]

yeah i watch guitologist and "uncle doug" amongst others but i would like to see the thorough method you use on your radio's i.e testing transformers,schematic tracing etc. keep up the good and interesting work!

[@electronicsoldandnew]

Geoff pickles : I might just do a video next time I have an interesting tube amp in for repair. Could be fun.

[@gaetanb738]

very interesting, thx

[@electronicsoldandnew]

You're welcome

[@chadhudson2046]

Does it come in 120v?

[@electronicsoldandnew]

Sure. Just use the appropriate transformers.

[@db1236]

What are the minimum voltage and current that digital meter can read?

[@andrew_koala2974]

MINIMUM VOLTAGE is ZERO

[@BjornV78]

31:50 Hi, how much VA is dat isolation transformer ?

[@electronicsoldandnew]

About 300VA if I remember correctly. I do mention it in the video

[@BjornV78]

@@electronicsoldandnew , i missed that clearly. I'm gonna build a dim bulb limiter with a classic isolation transformer of 400VA, inside the chassis of a old JVC JT-V11 Tuner, where the mainboard from is completely beyond repair, and is collecting dust for months. Now i know that this isolation transformer is strong enough. Thank you for the quick reply. Love your video's. Greetings from Belgium.

[@thomaspencak5811]

I have seen dim bulb testing when one takes out one wattage and changes it to a higher or lower wattage. Why not put bulbs in series to accomplish that, as that seems more logical. You could use switches that close (in off position) so all you need to do is switch them progressively to incrementally add resistance instead of changing lamps in a one bulb tester.

[@electronicsoldandnew]

This system for me is the most logical. It works well and has served my purposes.

[@LitchfieldCountyComputer]

where did you get the isolation transformer?

[@electronicsoldandnew]

I actually had it wound for me. You can probably find one cheaper ready made.

[@LitchfieldCountyComputer]

I'm having issues finding a 120/240 transformer of sufficient capacity

[@electronicsoldandnew]

You need a 1:1 transformer, so 120 to 120 or 240 to 240, depending on what your mains voltage is where you live. Then just look for one that supplies about 500VA. Should be more than enough.

[@brianturner8698]

@@electronicsoldandnew im having trouble finding a usable transformer. I bought 2 old ILP toroidal transformers from fleaBay but with no wiring diagrams, so am now stuck after building the dim lamp box. How can i work out if either ILP transformer will work for this ? The model numbers are a little strange , "9T029" , and a "9T631" (which I think is their Gen9 "625VA"). But i have no clue on the wiring of either. Could you point me in the right direction ? thanks (I can find absolutely zero online about these two ILP transformers).

[@electronicsoldandnew]

I’m afraid I can’t tell you for sure. You can easily determine which wires are for the two windings - just test for continuity. Then it’s a question of determining which is the primary and which the secondary. You should test them with a small AC voltage and see what you get.

[@thijs199]

why the bypass?

[@electronicsoldandnew]

After confirming that there are no shorts or excessive current draw, I like to bypass the light bulbs to apply full mains voltage to the device.

[@costykali6930]

Niceeee !!!

[@davidburdett2320]

Can anyone point me in the right direction for an isolation transformer please? Amazon UK have them but they’re all different values and prices. A web link would be great thanks :)

[@electronicsoldandnew]

David Burdett : that is always the challenge. You’re more likely to find one one on RS components or some such supplier (I almost said napkin). Try get one rated at about 1amp output current. You probably will never need more than that. More is better but the prices can be crazy. I had mine wound by an old guy who still does that, but you need to find one locally or shipping gets expensive (they are heavy).

[@davidburdett2320]

Electronics Old and New by M Caldeira Hi, I’ve popped online to look for one but I can’t find it. Can you post a link, if that’s ok Thank you :)

[@electronicsoldandnew]

David Burdett : something like this, I think. Study the dataset carefully. uk.rs-online.com/web/p/din-rail-panel-mount-transformers/1232501/

[@davidburdett2320]

Electronics Old and New by M Caldeira Hi, I’m a little confused, sorry. I’ve checked the dataset and it gives 115v as a secondary? As I live in the UK, would I need 230v like this one ( web link below ) Thanks :) uk.rs-online.com/mobile/p/din-rail-panel-mount-transformers/0504228/

[@wd8ash]

I used two 3 way light socket and bulbs .With 2 lights I have 50 ,100,150,200,250,300 watt settings!!! wd8ash

[@electronicsoldandnew]

👍

[@antigen4]

hmmm i guess having the light bulb side plugged into neutral won't be helping anyone ... a lesson for me perhaps - i didn't think it mattered - i guess you'll still be able to detect a ground fault but it won't protect you if wired through the neutral

[@alfredneumann4692]

There is one big problem with this curcuit. In Germany you don't get the lightbulbs. The damned EU has killed them. Yes, i can calculate the resistors, no problem. But with bulbs its much more nicer. Cheerio.

[@electronicsoldandnew]

Alfred Neumann : you don’t get them in Portugal either. But .... I found a lot of them in old electrical shops as old stock, those that still exist because the old guy won’t give in to the big department stores of today. I also found them in Chinese shops, which I’m sure you have there too. Good luck.

[@alfredneumann4692]

Thank you for your answer. Old electrical shops....same problem, they don't longer exist :-( I just researched and found something at a German-Restseller named Pollin. Crazy..... Just saw your Graetz 4R417-Resto. Great!

[@kolinevans9127]

I had the same issue but I found a bunch of halogens 40w and 100w I’ll be interested to see the effects based on what I can see the resistance is similar but more linear?

[@electronicsoldandnew]

Kolin Evans : halogens won’t work.

[@kolinevans9127]

Electronics Old and New by M Caldeira re halogen why not? Also I’d have the isolation trans in a separate box and use each for a dedicated purpose much less risk re the bypass.

[@erin19030]

Dim bulb Radio TV service.

[@electronicsoldandnew]

:)

[@666kty3]

Why not just use a regular dim bulb tester and plug it into a "kilawatt" to watch the current draw?

[@electronicsoldandnew]

This one is more fun to build 😊

[@666kty3]

@@electronicsoldandnew I wish I had time for "fun". I can barely keep up with the repair work that comes in let alone build stuff for fun. I tend to think of the path of least resistance (pun intended).

[@electronicsoldandnew]

I quite understand. For me this a hobby, so I obviously approach it differently.