#4: The "All American Five" radio and isolation

[@mjg263]

Great video! When I was a kid it was so common for things like this to give you a shock that it’s hard to believe we survived. We had a Webcor tube record player with a metal tone arm that would give you a jolt if you had bare feet or touched a ground while operating it. Later on I had a Silvertone tube record player that did the same thing, I remember telling my dad but he couldn’t find anything wrong with it. I also had a Zenith AM/FM tube table radio that would deliver full line voltage to the chassis, it sat on a shelf right beside the radiator in my bedroom. One night I reached behind it to mess with the antenna while my arm was touching the grounded radiator and got knocked outta bed! Consumer Reports used to warn you about this problem and deemed some of these units “unacceptable” if knobs could be pulled off or live screws were exposed.

[@gwesco]

I grew up on vacumn tubes so I am very aware of the potentials involved. Kudos for using a fixed camera mount. So many of these restoration videos are shot hand held and it makes them almost unwatchable.

[@speed2998]

When I was a kid, I learned this lesson the hard way! Thanks for explaining so clearly to others. Just one suggestion: You might use a regular analog meter, such as a Simpson, for the demonstration. The audience would more clearly see the needle deflection.

[@Kitsaplorax]

Or a really bright light bulb.

[@earlmcgill5867]

Thank You for a nice clear explanation! I'm just now beginning to learn how to work on AA5's and have been wondering just how to make it safer. Also, after watching this, I went and immediately removed my unrestored AA5 from atop my grounded refrigerator; seeing that the chassis screws were less than 1/2" from touching the refrigerator!

[@radiophonotvnut9024]

when I was a kid, I had a 1955 RCA all American 5 radio. I was down at the beach and a pair of shorts and I sat the radio on my knees to listen to it in to tune it. It shocked me so bad that I wet myself...lol

[@okaro6595]

Using ungrounded mains powered devices outside is not a good idea. That is the reason why in Europe you cannot connect ungrounded sockets to grounded outlets.

[@ChadQuick270W]

Thanks for the very informative video. I’ve got some older electronics myself that mention reversing the line cord to reduce hum but I assume they’re not a positive chassis. I’ve never been zapped and don’t try to service them myself. I guess this is why the polarized line cord came to be. Thanks for the cool video 😎

[@electronbob6676]

Thanks for the video! Just a quick comment, that at around 7:58 into the video when you were using the probes, you said there was no mains voltage showing up, but it appears to me that it was. .. thanks

[@bulldogavenue]

Thanks for sharing your knowledge!

[@FluxCondenser]

Nicely presented.

[@tomk4484]

Great video. Thank you for the clear, concise and easy to follow explanations. I have several of these radios to either restore, or validate previous owners’ restorations.

[@jamesmiles7878]

Excellent video! Very informative. Thank you!

[@notforkids4796]

I had a 1955 RCA All-American five radio. We were down at Rehoboth Beach for the summer, and I put the radio on my bare lap with my feet in the sand. I got shocked so bad, that I peed myself. My father thinking something was wrong with the radio cut the plug off. One of the two screws on the bottom had made contact with my leg outside of the shorts...

[@gabevee3]

I had never considered the position of the power switch on these. Of course it makes sense if one uses the polarized wire to make sure the power switch is on the hot side. Thank you.

[@hestheMaster]

Every would be restorer of old style electronics should watch this video. This is basically common sense for the uninitiated!

[@phantomphlyer4417]

Excellent video, thanks for posting!

[@pattyeverett2826]

Very good video. The only comment that I have is that I have the very Aretone radio in the video It does have a back that is missing in this video. However, as the video points out, the radio is no safer with the back on-the screws on the bottom and the knob shafts can still be lethal.

[@Landrew0]

It was an inherently dangerous cheap design, so the phrase "All American" was added to make it more appealing.

[@Kitsaplorax]

I'm likely missing something here, but wouldn't- 1. Wiring the switch to the hot side 2. Using a polarized plug that's properly installed 3. wiring a GFCI into the radio provide more than a measure of safety in an All American 5?

[@df9999999999]

Thanks for the information. I just restored a Majestic "Zephyr" radio from 1946. I installed a line cord with polarized plug and re-wired the switch to the hot line of cord, a pain as Majestic used the switch contact as a ground point for 6 or so components. My radio has two grounds in an attempt by Majestic to mitigate the safety issue. This AA5 radio has its chassis semi-isolated from the rest of the circuit with a .05uF capacitor in parallel with a 220k resistor. This limits the current, but both the cap and resistor will pass AC. I figure the reactance of the .05 cap to be at 53K at 60 Hz. In parallel with the 220K resistor or about 42.7K ohms. This will still pass 2.8mA of AC current, enough for a nasty shock or even death. Better than a dead short through your body, I guess! Perhaps an in-line GFI after rewiring would be prudent. As a kid, I got bit by these radios all the time.My family had an aluminum-cased RCA that was a particular offender. This was used in the garage and outdoors and regularly produced yelps of surprise when re-tuned. I'm amazed we all survived!

[@SeekingTheLoveThatGodMeans7648]

In principle the chassis should have been insulated from the aluminum case of the RCA, but if somehow a spacer or grommet was omitted on reassembly after taking it apart, that would cause the case to be electrically connected to the chassis. Another possibility is significant stray capacitance between the chassis and the case, both being metal objects with a large surface area in close proximity.

[@nor4277]

Until I can afford certain pieces of equiptment ,how about a safety capciator and or a fuse.or if I tough a volume knob to make sure I dont touch anything else ,and yes getting shocked is something I fear I been blasted a couple times when I was younger.Thanks for your video ,can I ask what did you pay for your isolation transformer and where did you buy it at.

[@okaro6595]

Did you remove the back plate or how on earth is the chassis exposed?

[@stevewahl5041]

What mistake was made that the Artone starting around 6:33 was not safe? I would guess that the hot lead was wired to the switch, but the switch was not rewired, so when the switch is on, the hot is connected to the chassis?

[@Ira06002]

First “thank you” sincerely for saving my life, since I’m very new to radio restoration. I bought a Varik. Is that the same as an isolation transformer? Also I’m currently working on my first AA5 project a Hallicrafters 5R33 AM/SW so what do I look for to ensure I use an isolation transformer? I did learn never to plug in an old radio which I have not done so far. Thank you once again. Steve

[@radiophysicsandelectronics6923]

A Variac (also known as an autotransformer) provides no isolation. The variac and the isolation transformer are different. There are on line resources describing the need for and proper use of both variacs and isolation transformers available at the Antique Radio Forum (there are numerous threads, see, e.g., www.antiqueradios.com/forums/viewtopic.php?t=62638 and www.antiqueradios.com/forums/viewtopic.php?f=8&t=194901) and you can also ask questions there. See also the excellent kzbin.info/www/bejne/jnPWgmapj5lofM0.

[@nor4277]

I found variact ebay as low as 39.00

[@midmodaudio6576]

Great video, thank you !

[@nor4277]

Thank you for this lesson,I just bought a 1953 Sears Silverstone,I got a feeling it's a hot chais,I haven't open it yet I will soon to order caps for it ,I am thinking of getting a isolation transformer ,I found a good price for a new one ,if you no anything about my 1953 Silverstone radio please let me no ,I hate getting shocked,I am going to try the method you are showing us for testing it ,do you recommend replacing the cord ,the plug it has on it ,I can switch the wires around ,if you think that idea is ok ,please let this old man no,I did buy a replacement plug for it ,pretty much the same .thanks again for your safety video

[@radiophysicsandelectronics6923]

I'm glad you found the video interesting. I strongly urge you to learn more about radio repair and restoration before working on your radio or anything related to mains power, which can be lethal. The Antique Radio Forum, antiqueradios.com/forums/viewforum.php?f=8&sid=3279a08b28998acdefc23bd2285bd047, has such information and can provide guidance, as can other sources. Please be aware that there are different types of isolation transformers, and not all provide the needed isolation. See, e.g., www.antiqueradios.com/forums/viewtopic.php?f=8&t=120898 and other similar threads at that site.

[@johndonsky2998]

I may be mistaken, but at around 8:00 where the set is off, isn't your meter also saying over 120 volts?

[@paulsto6516]

That was millivolts, as denoted by the small "m" in the reading. It got me at first too.

[@rawtry65]

Do you have a video for the rewiring the radio to be safe?

[@ATonkaTruck]

Excellent. Thank you.

[@Captain_Char]

I don't need to know the warnings of a hot chassis on a radio, a long time ago we had one of those round vintage fridges, that was ungrounded, and next to the fridge was the light switch for the room, which had a stainless steel cover, naturally id turn oin the light while opening the fridge, but in doing so id complete the ground leg of the fridge and get this buzzing feeling through my entire body, id let go, but this would happen a few times before I learned my lesson, its not a fun feeling either I might add

[@okaro6595]

These are the reasons in Europe you cannot plug an ungrounded (not double insulated) plug in a grounded socket but can do the opposite.

[@tinkeringwithelectronics]

Great demo. Well said

[@bxb590]

Well done.

[@fredmartin153]

So if I am using an O Scope to test this type of radio,should I plug the scope into the isolation transformer along with the radio,or is it okay to leave it plugged into the house mains? Which is safer?

[@hestheMaster]

The radio should be plugged into a variac then plug that into an isolation transformer . You can safely use the oscilloscope as normal. But before doing so make sure the radio has a polarized plug and the neutral line goes into the line from the filaments AND the other side ( hot) is switched that goes to the filaments and bulb. As the video shows don't assume that someone else has just put a polarized plug on it without checking the circuitry!

[@erin19030]

Run it off a battery supply

[@greghawkins1025]

I remember, years ago, when I first encountered these safety plugs in which one prong's wider than the other, I didn't understand their purpose. It was inconvenient to plug them in the right way so I ground them all down with a motorized grinder so they'd fit the socket either way. I was wrong & beg you for your electrical forgiveness.

[@erin19030]

This is all well and good as long as the mains and extension boxes are wired correctly too. My test bench has a Variac feeding an isolation transformer with a dim bulb series limiter. The hot and neutral wires can be reversed after it leaves the breaker box. The only safe option is a ground fault interrupter and that still requires the DUT to be wired correctly. Many of these Radio restorers are more concerned with cosmetics. The AA5 came about to be so popular as a result of the WWII effort. Transformers required miles of copper and the military came first.

[@nivlac5]

What is the make and model of the big red isolation transformer? Tnx, Dean

[@radiophysicsandelectronics6923]

As I recall, I got the isolation transformer from Jameco. It's rated at 300 VA. The current model is www.jameco.com/z/ITR300-Power-Transformer-Isolation-120VAC-120VAC-300Va_181315.html

[@larryclark9380]

Thanks for the warning!

[@Tricknologyinc]

At 7:55 you are in fact reading full line voltage when you say you are not! Are you blind? The readings were identical for both off and on! [Ooooops, Nevermind! Missed the mV indicator! Freaky that it happened to be 121!]

[@WardCo]

No, I thought that too -- but he's reading millivolts in the first case.

[@Tricknologyinc]

@@WardCo Thanks! My tunnel vision is getting worse these days! Appreciate the heads up!

[@philliplucaroni7806]

back then people wernt stupid like they are today