5 tube AC/DC and safety.

[KA5PIU]

Hello.

I took an old (Octal tube) 5 tube AC/DC radio apart for repairs and wanted to understand the lack of safety in a hot chassis so I decided to experiment.
The very first thing I did was to isolate the filament string from everything else, in essence just a christmas tree light set, including the indicator lamp.
OK, no connection to chassis so far.
Next I isolated the audio section by way of the transformer and worked my way back.
I isolated every part of that radio to the standards of double insulated elecrical safety.
The loop antenna and speaker are isolated as well as the volume pot and tuning cap, in short, no short. ;)
I have tested the radio with a megger to be sure.
http://www.angelfire.com/electronic/funwithtubes/AA5-1.html
So the question now is this.
Why was this not done back then?
To be sure, the radio in question is now equipped with an IEC power connector and grounded chassis.

[W3WN]

That's how they built them in those days... cheap. No isolation transformer kept the costs down.

Not saying it was wise, but that's the way it was.

[W3MIV]

All you had to do to minimize the risk was to pay attention to the polarity of the line cord. The old pre-War II wiring that most of us had used the neutral as a pseudo-ground. Plug it in the wrong way and you had a hot chassis; plug it in correctly and you were "safe" -- maybe. I had an old Hallicrafters S38 (wish I still did) that my mother would unplug to dust and clean in my room; it was a lottery as to how the old lady would plug it back in when she finished. You'd find out as soon as you touched both the cabinet and the radiator next to it. But even then, line cords had a ribbed side and a plain side. The plain was the hot lead. To my knowledge, that convention is still followed.

Just another reason why the "nanny gummint" a lot of you guys whine about moved to mandate polarized and grounded cord sets and an unbroken ground line for all house wiring.

[n2ize]

All you had to do to minimize the risk was to pay attention to the polarity of the line cord. The old pre-War II wiring that most of us had used the neutral as a pseudo-ground. Plug it in the wrong way and you had a hot chassis; plug it in correctly and you were "safe" -- maybe. I had an old Hallicrafters S38 (wish I still did) that my mother would unplug to dust and clean in my room; it was a lottery as to how the old lady would plug it back in when she finished. You'd find out as soon as you touched both the cabinet and the radiator next to it. But even then, line cords had a ribbed side and a plain side. The plain was the hot lead. To my knowledge, that convention is still followed.

Just another reason why the "nanny gummint" a lot of you guys whine about moved to mandate polarized and grounded cord sets and an unbroken ground line for all house wiring.

Very true. And, if you do experiment or use old electronics these days its assumed you would have the knowledge to realize what may dangerous to touch.

Much like the old antique electric fans that I restore. The old guards surrounding the blades were wide spaced and easy to get your finger nipped. Of course it doesn't happen because we have the sense not to stick our fingers in the blades. Even as a little kid I knew that you don't put your finger near the fan.

[NQ6U]

Even as a little kid I knew that you don't put your finger near the fan.

Well, maybe you did...

---Carl, AKA "Stumpy"

[N2NH]

What you grounded a perfectly good hot radio? When I was a kid I spent many a waking hour licking my burns after being shocked by the radio.

[n2ize]

Well, maybe you did...

---Carl, AKA "Stumpy"

Don;t tell me you stuck your finger in the fan ?? :( :(

[KA5PIU]

Hello.

Finished with the 5 tube AC/DC.
It is still a 5 tube radio but the rectifier is gone.
The audio output is now a push pull configuration and half of that is a transistor.
The filament string is still on the AC line but totally isolated from the chassis.
For HV I took parts from a computer power supply and stripped the windings from the toroid and used everything else, a true switcher.
Now there is a 6 volt winding and a 45, 90, and 300 volt tap winding.
The original speaker I replaced with a modern car radio unit.
As safe as a 5 tube AC/DC can be made.
And it cranks!
One 6L6 and a FET make up the audio output, nearly 20 watts of audio.
I needed a good load for the power supply as this is a switcher and can not wait for tubes to warm up.
It looks and acts like a tube radio should but with really killer sound.

[W1GUH]

Don;t tell me you stuck your finger in the fan ?? :( :(

Well I haven't, but I know a few loonies that must have -- just to hear the sound it makes!!!

OTOH, I'm the guy that liked to stick screwdrivers in the power socket because I liked the feel of a shock!

[NQ6U]

Don;t tell me you stuck your finger in the fan ?? :( :(

I did. It was an accident but I had to have the very tip of my right ring finger stitched back on. It's still a bit numb to this day.

[N2CHX]

The older I get the more I realize I really am a masochist. I used to take the leads from the 70 volt output of an PA amp and put them on my tongue to see how high I could crank the knob before I couldn't take it anymore.

That sounds so much like something Rudy would do it's pretty scary.

I have whips and candles if anyone would like to join me in the back room.

[K7SGJ]

Back room? Hell I'll meet you out front!

[KA5PIU]

The older I get the more I realize I really am a masochist. I used to take the leads from the 70 volt output of an PA amp and put them on my tongue to see how high I could crank the knob before I couldn't take it anymore.

That sounds so much like something Rudy would do it's pretty scary.

I have whips and candles if anyone would like to join me in the back room.

Hello.

I do not do such things to myself with intent.
I do however possess a pair of electric spurs that I can dispense electrical joltage with great pleasure. ;)