Thanks for the video. Forgive my ignorance here, but this is something I've never understood. Why is commercial power dangerous? Why is it more dangerous than the 120VAC from the iso trans?
Rick, if I understand correctly "isolation transformer" is recommended whether the DUT has the 3 or 2 prong power chord. For 3 pronged DUT's, you recommend the use of an isolation transformer with DUT's grounding plug left open - providing complete isolation from commercial power. Is this correct?
If you use a commercial ground on the isolated side there is a chance of getting a shock from commercial power. If there is no ground then there is zero chance of getting shock from commercial power.
i followed your advice but should have asked for more, i got one. it is rated at 270 VA. im not sure what that means. but if i plug in a drill it blows the fuse so i dont know what good it is. can you explain pls what 270 VA is? thanks
Hi Rick ,I wonder when you get time if you could make a tutorial on how to wired the ac line cords to the ac-dc 5 tubes sets so they will be safe as possible. I always am confuse about these radios and how one side of the line is chassis ground and if you use a non polarized cord the chassis can be hot. Some have a capacitor to protect from this but I just dont really understand the correct method. Maybe you can get me thinking the correct way of wiring these radios. Many Thanks Cliff Dice W8WHO
What ever I am working on is plugged into the isolation transformer. It keeps me safer and also keeps the test equipment safer because what you are working on is isolated from the commercial power and its ground too.
i think i get it now. you cant short between the isolated circuit and something that is plugged into mains voltage because the isolated circuit is isolated from mains voltage. right? i can still zap myself with the potential difference between the two terminals of the isolated circuit but i cant create a short between the isolate circuit and mains voltage. right?
im going to be working on a tube amp so i want to be sure i have all these concepts clear in my muddy head
Plus the power out of the isolated side is enough to work on radio/TV chassis. It is still dangerous but not like the danger that comes from commercial power socket.
This is great to know, I'm currently getting my caps ready for my Philco. Thankyou for showing this, besides making your own....wheres the best place to purchase a I.T. Cost an quality?
A.E.S. (Antique Electronic Supply) has a number of them, just search on there website for isolation transformer. I found a number of places online. I would also look for a Ham Fest or Antique Radio Show/Sale/Club/Event. Thanks.
Yes, but you must try much harder. With and isolation transformer you can only get a shock only from the secondary side. With out and isolation transformer you can get a shock from everywhere.
Wondering why you wouldn't use the 6.3V windings. If it's from a TV there should be more power available from there. The 5V would only power the rectifier.
I was able to find a noise-filtering IT off of eBay. You're right, they're a gotta have.
You can if there is no 5VAC. But if there is, the 5VAC this winding is closest to the center core of the transformer and is designed to handle the highest current. It is the high current that provides the strong magnetic field.
If you want to use the earth ground it would be only used on the commercial power side. If you put the transformers in a metal box, the metal box would be connected to earth ground. The isolated side remains a two wire outlet only, no earth ground. So if you use a three wire socket on the isolated, there is no connection to the earth ground terminal.
Good job on the video Rick. Verry nice and may I add saftey is allways first. Working on radio's is fun to see them come back to life with with a little TLC. So dont let the fun blind you to safety after all my teacher said so right Rick
I have used this idea to build a huge isolation transformer out of transformers salvaged from some old computer terminals which had linear power supplies. Also I have a Heathkit variable isolation transformer which seems very rare, it has a voltmeter and adjustment from 90-130 volts AC.
I think I saw a glimpse of that isolation transformer in a few of you videos, it is huge. A great use for those transformers. Neat, a Heathkit variable isolation transformer, that would have to be rare. I have completed several Heathkit courses, they are great. I really enjoyed them. Thanks.
It also has to do with the construction of the transformer. Both the 120VAC and the 5VAC windings are at the center of the transformer core. The high voltage windings are farther out from the core.
Hey Rick I got a medical isolation transformer, 130VA, but measuring the isolated side (either lead) to ground, I see 30 volts with a DMM. Is that OK? I connected it to the radio. It works but still see 30 volts from from chassis to ground (aka ground of the oscilloscope probe). I don't want to blow up the scope. I'm sure there is very little current to ground, but is this normal. This is the transformer (A41-130-230) I am using.
google: signaltransformer com/Data/Datasheets/A41 pdf
They have a tremendous selection with all things that have windings. Your isolation transform should handle any project. The most important part of the workbench.
I called the manufacture of my transformer. There's always some capacitance couple from secondary to ground, it's normal apparently. I measured voltage with a big resistor across one side of primary to ground. The voltage went from 30V (no load) to 0.05V.
Can I ground a AC-DC radio chassis, if it's on an isolation transformer?
The probe ground on the oscilloscope grounds the chassis, but is there a clever way to drain the small ground current off, so it does not go through the scope?????
If you do that, make sure that if there are any capacitors going from line to chassis that they are good. Or better still, replace them with safety rated caps. If the caps are leaky they may blow if you ground the chassis.
An IT is kinda old school for me, but I do have one collecting dust down there - lost in that mess of a workbench somewhere.
I use an APC battery backup UPS, you can have NO connection to the mains and run off the battery for tests, since it uses an inverter to run off a 12V SLA battery. They also have good protection in them, and will shut down if there is a short. They also come in handy if there is a power failure to make your rigs run on bettery. I actually ran my boiler off of one!
From ebay, I got a variac with the IT built in the same box, looks like it was from the 50s. That thing is heavy, and rated at five amps. But Rick is right, not a good idea to connect directly to the mains, I have been guilty of this at times. My smaller variac has a 3 amp fuse.The combo is too heavy to remove from the bench. So I like using the APC-UPS for off bench tests. They are NOT only for confusers and have many applications.
I have been giving some pointers to a YouTuber, Kevin, on repairing his Grand dads console radio. He bought the capacitors and replaces the old ones. Then I got a help email a few days later and by the time I email him back he had figured it out. His Grand dads radio is playing great. Then I email him about getting an isolation transformer. Lol, He emailed back saying he had been paying attention. That was the first thing he did was to get the Isolation Transformer and Variac.
A ground fault circuit interrupter would be great for everything in the room. I also recommend in my books that you stand on a clear plastic floor mat. Colors like black may have carbon in them and you don't want to stand on that.
I hope you don't think this is a dumb question, but as far as getting shocked is concerned, is the advantage of having the isolation xfmr mainly due to the lower current at the secondary/isolated side? I'm not quite clear on that. I greatly appreciate your videos and information.
That is an excellent question! The big advantage is, that the test chassis that is plugged into the isolated power is isolated from commercial power. This means when you are working on the test chassis and if you happened to touch it and anything else that is plugged into commercial power at the same time, you will not receive a shock. Also all the test gear, like an oscilloscope plugged into commercial power, can be safely hooked up to the test chassis.
I did this using 2 matched power transformers that came out of a couple of cassette decks that I don't use anymore, and they were connected back to back like in your video, but I got a very high voltage out of the second transformer, much higher than the commercial power, it must have been up in the kilo volts range, because it fried my volt meter when I tested it.
Thanks for the video. Forgive my ignorance here, but this is something I've never understood. Why is commercial power dangerous? Why is it more dangerous than the 120VAC from the iso trans?
danieldempseymusic 9 months ago
@danieldempseymusic
Because you are surrounded by commercial power. Many more chances to get a shock with at least 40amps of power.
AllAmericanFiveRadio 9 months ago
Would it be the same if its only one transformer with 120 in 120 out
Or is it better to have the step down and then step up ?
Bonitabonitabonita 1 year ago
@Bonitabonitabonita
120 to 120 would be better, and that is how my commercially made isolation transformer is made.
AllAmericanFiveRadio 1 year ago
Rick, if I understand correctly "isolation transformer" is recommended whether the DUT has the 3 or 2 prong power chord. For 3 pronged DUT's, you recommend the use of an isolation transformer with DUT's grounding plug left open - providing complete isolation from commercial power. Is this correct?
451mnu 1 year ago
If you use a commercial ground on the isolated side there is a chance of getting a shock from commercial power. If there is no ground then there is zero chance of getting shock from commercial power.
AllAmericanFiveRadio 1 year ago
i followed your advice but should have asked for more, i got one. it is rated at 270 VA. im not sure what that means. but if i plug in a drill it blows the fuse so i dont know what good it is. can you explain pls what 270 VA is? thanks
iorixs 1 year ago
This setup is for radio chassis which draws on more than 1.5 amps.
AllAmericanFiveRadio 1 year ago
Hi Rick ,I wonder when you get time if you could make a tutorial on how to wired the ac line cords to the ac-dc 5 tubes sets so they will be safe as possible. I always am confuse about these radios and how one side of the line is chassis ground and if you use a non polarized cord the chassis can be hot. Some have a capacitor to protect from this but I just dont really understand the correct method. Maybe you can get me thinking the correct way of wiring these radios. Many Thanks Cliff Dice W8WHO
W8WHO 1 year ago
I have put it on the YouTube to-do list.
AllAmericanFiveRadio 1 year ago
so if i use a usb o'scope and waveform generator an isolation transformer can save the computer from getting fried?
iorixs 1 year ago
What ever I am working on is plugged into the isolation transformer. It keeps me safer and also keeps the test equipment safer because what you are working on is isolated from the commercial power and its ground too.
AllAmericanFiveRadio 1 year ago
i think i get it now. you cant short between the isolated circuit and something that is plugged into mains voltage because the isolated circuit is isolated from mains voltage. right? i can still zap myself with the potential difference between the two terminals of the isolated circuit but i cant create a short between the isolate circuit and mains voltage. right?
im going to be working on a tube amp so i want to be sure i have all these concepts clear in my muddy head
iorixs 1 year ago
Correct to all the above.
Plus the power out of the isolated side is enough to work on radio/TV chassis. It is still dangerous but not like the danger that comes from commercial power socket.
AllAmericanFiveRadio 1 year ago
if i plug in to the wall with a bear wire and hold both ends firmly in my hands and stand in puddle of salty water i will get dead right?
if i plug into an isolation transformer and hold both ends firmly in my hands while standing in the puddle i wont get dead?
iorixs 1 year ago
This is great to know, I'm currently getting my caps ready for my Philco. Thankyou for showing this, besides making your own....wheres the best place to purchase a I.T. Cost an quality?
53packardclipper 2 years ago
A.E.S. (Antique Electronic Supply) has a number of them, just search on there website for isolation transformer. I found a number of places online. I would also look for a Ham Fest or Antique Radio Show/Sale/Club/Event. Thanks.
AllAmericanFiveRadio 2 years ago
I don't get it. Can't you get a lethal shock from the isolated side too ?
verymaddog 2 years ago
Yes, but you must try much harder. With and isolation transformer you can only get a shock only from the secondary side. With out and isolation transformer you can get a shock from everywhere.
AllAmericanFiveRadio 2 years ago
Wondering why you wouldn't use the 6.3V windings. If it's from a TV there should be more power available from there. The 5V would only power the rectifier.
I was able to find a noise-filtering IT off of eBay. You're right, they're a gotta have.
trojanrabbit74 2 years ago
You can if there is no 5VAC. But if there is, the 5VAC this winding is closest to the center core of the transformer and is designed to handle the highest current. It is the high current that provides the strong magnetic field.
AllAmericanFiveRadio 2 years ago
Safety is always first !
I ALWAYS USE an isolator while working on my radios as well !
One time there was a failed xformer and good thing I had a fuse and isolator in line :)
patchcords 2 years ago
Glad to hear you use an isolation transformer it is very important for safety.
AllAmericanFiveRadio 2 years ago
How would you connect the ground for three prong devices?
thejoerusso 2 years ago
If you want to use the earth ground it would be only used on the commercial power side. If you put the transformers in a metal box, the metal box would be connected to earth ground. The isolated side remains a two wire outlet only, no earth ground. So if you use a three wire socket on the isolated, there is no connection to the earth ground terminal.
AllAmericanFiveRadio 2 years ago
Good job on the video Rick. Verry nice and may I add saftey is allways first. Working on radio's is fun to see them come back to life with with a little TLC. So dont let the fun blind you to safety after all my teacher said so right Rick
L0WRYDER 2 years ago
Yep, safety first. It is a very good habit to get into.
AllAmericanFiveRadio 2 years ago
I have used this idea to build a huge isolation transformer out of transformers salvaged from some old computer terminals which had linear power supplies. Also I have a Heathkit variable isolation transformer which seems very rare, it has a voltmeter and adjustment from 90-130 volts AC.
retrochad 2 years ago
I think I saw a glimpse of that isolation transformer in a few of you videos, it is huge. A great use for those transformers. Neat, a Heathkit variable isolation transformer, that would have to be rare. I have completed several Heathkit courses, they are great. I really enjoyed them. Thanks.
AllAmericanFiveRadio 2 years ago
It also has to do with the construction of the transformer. Both the 120VAC and the 5VAC windings are at the center of the transformer core. The high voltage windings are farther out from the core.
AllAmericanFiveRadio 2 years ago
Hey Rick I got a medical isolation transformer, 130VA, but measuring the isolated side (either lead) to ground, I see 30 volts with a DMM. Is that OK? I connected it to the radio. It works but still see 30 volts from from chassis to ground (aka ground of the oscilloscope probe). I don't want to blow up the scope. I'm sure there is very little current to ground, but is this normal. This is the transformer (A41-130-230) I am using.
google: signaltransformer com/Data/Datasheets/A41 pdf
gmcjetpilot 2 years ago
They have a tremendous selection with all things that have windings. Your isolation transform should handle any project. The most important part of the workbench.
AllAmericanFiveRadio 2 years ago
I called the manufacture of my transformer. There's always some capacitance couple from secondary to ground, it's normal apparently. I measured voltage with a big resistor across one side of primary to ground. The voltage went from 30V (no load) to 0.05V.
Can I ground a AC-DC radio chassis, if it's on an isolation transformer?
The probe ground on the oscilloscope grounds the chassis, but is there a clever way to drain the small ground current off, so it does not go through the scope?????
gmcjetpilot 2 years ago
Try a 0.2 MFD @ 630V to ground the chassis. It is not perfect but it is pretty good.
AllAmericanFiveRadio 2 years ago
If you do that, make sure that if there are any capacitors going from line to chassis that they are good. Or better still, replace them with safety rated caps. If the caps are leaky they may blow if you ground the chassis.
trojanrabbit74 2 years ago
The 5VAC is high current and that produces a very strong magnetic field. The high voltage windings are low current.
AllAmericanFiveRadio 2 years ago
An IT is kinda old school for me, but I do have one collecting dust down there - lost in that mess of a workbench somewhere.
I use an APC battery backup UPS, you can have NO connection to the mains and run off the battery for tests, since it uses an inverter to run off a 12V SLA battery. They also have good protection in them, and will shut down if there is a short. They also come in handy if there is a power failure to make your rigs run on bettery. I actually ran my boiler off of one!
umajunkcollector 2 years ago
Sure that will work. A UPS is an Isolation Transformer with an inverter.
AllAmericanFiveRadio 2 years ago
Rick good job on the video the new setup looks good. Hope you make some more video's soon on all test equipment.
L0WRYDER 2 years ago
That's a good idea. Thanks
AllAmericanFiveRadio 2 years ago
Rick,
I've always wondered what type of isolation transformer you use. Now we all know. Thanks.
I have a two-plug isolation transformer that was purchased on line. It and a variac were the first two items I bought. Better to be safe than dead.
Regards,
John
joernone 2 years ago
From ebay, I got a variac with the IT built in the same box, looks like it was from the 50s. That thing is heavy, and rated at five amps. But Rick is right, not a good idea to connect directly to the mains, I have been guilty of this at times. My smaller variac has a 3 amp fuse.The combo is too heavy to remove from the bench. So I like using the APC-UPS for off bench tests. They are NOT only for confusers and have many applications.
umajunkcollector 2 years ago
Hey John,
I have been giving some pointers to a YouTuber, Kevin, on repairing his Grand dads console radio. He bought the capacitors and replaces the old ones. Then I got a help email a few days later and by the time I email him back he had figured it out. His Grand dads radio is playing great. Then I email him about getting an isolation transformer. Lol, He emailed back saying he had been paying attention. That was the first thing he did was to get the Isolation Transformer and Variac.
AllAmericanFiveRadio 2 years ago
What do ya think aobut using a GFCI too?
umajunkcollector 2 years ago
A ground fault circuit interrupter would be great for everything in the room. I also recommend in my books that you stand on a clear plastic floor mat. Colors like black may have carbon in them and you don't want to stand on that.
AllAmericanFiveRadio 2 years ago
I hope you don't think this is a dumb question, but as far as getting shocked is concerned, is the advantage of having the isolation xfmr mainly due to the lower current at the secondary/isolated side? I'm not quite clear on that. I greatly appreciate your videos and information.
Barnekkid 2 years ago
That is an excellent question! The big advantage is, that the test chassis that is plugged into the isolated power is isolated from commercial power. This means when you are working on the test chassis and if you happened to touch it and anything else that is plugged into commercial power at the same time, you will not receive a shock. Also all the test gear, like an oscilloscope plugged into commercial power, can be safely hooked up to the test chassis.
AllAmericanFiveRadio 2 years ago
There is no possible electrical path between the test chassis plugged into the isolated power and anything plugged into commercial power.
AllAmericanFiveRadio 2 years ago
I did this using 2 matched power transformers that came out of a couple of cassette decks that I don't use anymore, and they were connected back to back like in your video, but I got a very high voltage out of the second transformer, much higher than the commercial power, it must have been up in the kilo volts range, because it fried my volt meter when I tested it.
CoolDudeClem 2 years ago
Ooops! I know this setup works because I have made this before. But careful testing is always a must. Imperative!!!!
AllAmericanFiveRadio 2 years ago