Hey, thanks a lot for taking the time to explain everything in such detail and with great demonstrations. This is definitely one of the best safety videos I've ever watched. I really appreciate it.

Plain language, straight forward and one of the best presentations I have seen! You get my thumbs up. Although the explanation all the way from the utility pole might seem elementary we all need a reminder. 5 stars!

Soothing education. It was like meditation for me.

One of the most thorough explanations I've heard yet, many thanks for taking the time. 👍🏾👍🏾

Great video. I also plug that Kill a Watt into the DBT, and the UUT into the Kill a Watt, set to Watts or V.

Thanks for sharing a very clear schematic of your setup. This is about the fifth video on this topic I’ve watched today (and the last). But you’ve inspired me to get cracking on building my own; I believe I have couple of old AC voltmeters and ammeters laying around the shop, I didn’t realize I was saving them for this project.

Reply to Erik Burman: The human body's resistance varies widely depending on who you are, what your body chemistry is and most importantly, if your skin is moist or sweaty (usually with a lot of salt mixed in). It only takes a few milliamps of current to seize muscles or stop the heart from beating. So yes, there are a lot of variables.

Thanks for showing the Dim Bulb current limiter. I also learned today that a Variac has only a single winding. A Variac is not constructed the same as a variable transformer.

Thanks for the very elegant demonstration of the value of each item, and the sequence to use. I shall incorporate these ideas into my test bench!

Excellent! Thanks for this. Very useful bit of kit for working on older valve (tube) electronics. Now, the pain of all the old bits that were thrown out of the lab years ago suffering from 'I will never need that old thing anymore' syndrome!

Wow so good...! I'm a newbie to all this and have been following a good few amp techies on KZfaq, This has cleared the fog about the current limiter (dim bulb use) Thanks for sharing...Ed..uk..😀

Good video, thanks!

Thank you. A good demo video.

I liked the demo towards the end where you show lower voltage on the tested item if the dim bulb has too low of a wattage. I'm hoping with the phase out of incandescents that we won't have shortages of 150 or 300 watt bulbs in the distant future!

Nice presentation.

Thank you for your efforts to teach us! Much appreciated! Suggestions = IMHO, an Emergency All-Stop Switch should be the first device in the chain, from the mains supply wall socket. It should be of the proper industrial design, meaning 1) it is not just a common paddle-type wall switch, but rather 2) an ergonomically designed safety switch, a) meaning it has big button(s) that are easily accessed and brightly colored, as to their function. b) Further, IMHO, the single switch type, having a large mushroom shaped button, is better than the two switch type, because it simply can not be confused, during an emergency and 3) it should be placed in a predominate location, having unimpeded (at all times) access. I am, even presently, designing my AC Supply. I planned to use many 40 watt bulbs, in order to have a great amount of control, when raising the current supply. Accordingly, I purchased Halogen bulbs, because they are considerably smaller in size. After purchasing them, I saw a comment that common incandescent bulbs are better, but there was not an explanation, as to why. Do you know? I would rather adapt for them, now, before finishing the build. Final tip = I suggest that an AC supply system should be designed such that each component is strung together with the next by means of some type of connector. That way, each component can be employed for individual use, in other applications.

What is important to note is that most variacs have no isolation at all, one side of the output always gonna be live of it and the other just tapped voltage from it pretty much, you want to use your isolation transformer if you measure anything in live voltage to protect your scope. I got my big Variac first actually way back in time but later I got a very big nice isolation transformer that even have virtual ground. I put a switch on the ground circuit to be able to run either isolated live without ground or together with virtual ground. it is a great thing to have if you were to work on a tube radio that works without both ground and transformer, yeah the death radios and I don´t like them. but you never get better than your tools I always say, but your tools also don´t have a brain you you have to use your own. Just because you have fancy isolation and variacs you won´t be completely protected which you always should have in mind. Don´t put too much trust in your extra safety

You're hilarious. And thank you for the well-informed and info

I have one similar i made. I like the voltage meter! i will incorporate that.I don't have a bypass switch... what i do is have a Two Bulb Y screwed into the bulb socket that way I can add different wattage bulbs to make up different wattage protections, and if i need by pass to full power I just screw in a 15 Amp fuse which will bypass the bulb completely. Brought up my old signal generator yesterday 10 volts every 15 mins or so, but was wondering what the precise voltage was? I need a AC volt meter in line.jim

I'm a little confused on this. You said to keep your oscilloscope on the primary side of your transformer. Your oscilloscope is grounded through the ground clip. How does this prevent your oscilloscope from blowing up if you attach your ground clip to something that is live?

1:18 also bond vs Jaws on the train, electric bulb electrodes to the dental work, classic ...

Outlet>Isolation>Variac>Current limiter>What you are working on

Any suggestions for make and model# of an isolation transformer? I've seen lots available but am not completely sure which one I need for working on tube phonographs from the 1950s. I've got some education in college days (so not completely unfamiliar). Just want to start right.

I bought from a garage sale what I believed to be an isolation transformer, but when I have the transformer output connected to a working load, if I measure the potential between the output live to earth ground, (to convince myself I am not going to get a shock), I read 129V, and from the output neutral to earth ground I read 43V. However, prior to doing this load test, with every wire disconnected, all Megger tests of the primary and secondary with respect to each other and the earth terminal on the core, show it all as good, i.e. no path of conduction where there shouldn't be. Would your isolation transformer show any potential difference on the output, between itself and earth ground? Can you show that? Is it possible that the primary voltage and secondary voltage levels, just float around with respect to one another, until some load, even infinitely small would couple them, then the PD would become zero? Because when I insert a load where I measure the 129V potential, then measure the potential across that load, it reads zero.

What is the formula to calculate the bulb wattage needed related to the device?

Useful video thanks. When do you utilize a gfci or quick blow fuse in your testing bench? The floating vs non floating contradiction in recommendations still baffles me also, especially related to Oscopes. Cheers

Thank you for the informative video. I am putting together the same device 'isolation transformer -> variac -> dim bulb', and this video helped a great deal. I was thinking about putting the items together in one test box. I noticed your design does not include a fuse or circuit breaker. Would it be beneficial to add one? If so - can you give me your advice on where it should be placed (at the input to the transformer or at the output - or both) and what amp fuse would be best in relation to the transformer you used.

Since the secondary of the variac (and the primary) has no connection to earth ground what is the purpose of the isolation transformer? In its absence you will have the variac connected to the dim bulb and load. If you were to touch line voltage in your load (or attach ground lead of o-scope to it) there is no complete path back to voltage source. Please explain.

Hello, I read that measuring with an oscilloscope, you need an amplifier, you need galvanic separation, I ask from what point of view, when today's amplifiers have only 2 wires. Thank you for any knowledge

My isolation transformer is only rated 500 va, while my variac is rated 2 kva. Should I still put the isolation transformer first?

Thanks for the video. If a reason for not putting a variac before an isolation transformer is that the isolation transformer won't develop enough counter emf and could burn out at lower voltage. Then is it also a bad ideal to place a variac before the mains transformer of your favourite Fender Bassman?

I found an old isolation transformer, very heavy 115v .500va. I replaced the incoming cord because the insulation was cracking. The transformer looks unused. I checked for continuity and short to ground on both sides and it was good, it has a single receptacle. After plugging it in to check output voltage at 127v, but there was also 17v on the ground side to chassis ans 96v from hot side to chassis. I am no electrician, is this transformer trash ? Thanks.

How can I maintain isolation if my variac has an earth ground plug?

I think I have those exact isolation transformer and variac.

Never actually seen a transformer like that anywhere where I live (finland), I only recall having seen a few large stations that took up the space of a house and a yard, wired off with large metal fences and lots of buildings and electrical equipment, whole place makes a hummmmm sound. One station serves many thousands of households.

$2 for a 350VA isolation transformer? $5 for a metered Variac? Bargains of the century!

100 or 200 watts is way to high for low current devices like AA5 radios. Just sayen?

If I could find a large enough transformer, I could put both the test equipment and the device under test on the secondary of the isolation transformer. Is that any "down side" to doing that?

Great video. These couple of videos show "isolation" labeled products that one has to be very careful with. I guess this shows how one has to be careful with wording and verify in practice. Tripp Lite "isolation" transformer. kzfaq.info/get/bejne/g55keKuLms60cZc.htmlsi=xYoBQZtPcpm_Q_j2 "Variac with isolation transformer" kzfaq.info/get/bejne/btVne9d4udympnU.htmlsi=9kedZK-sP8bzlcbS

Barbecued chips? OR .....secret sauce iso's?

...and when incadescent bulbs become banned? In 2022 (even 2021) I would think you would be creating this video with an alternative to a dim bulb limiter...

Hey, just wanted to let you know I scrolled past the stupid key frame of you making an o-face for this video. If there had been a pic of that variac or anything technical, I would have watched.

If you need a dim bulb then you are the dimmest bulb in the dozen. Learn to use meters with that variac.