[morzh]

About 4 years ago a colleague presented me with an auld audio oscillator that was once a Bell Labs property and is an AT&T product - built by Western Electric.
It was obviously mounted in some rack.
I haven't plugged it in as the input jack is non-standard.

So recently (days ago) I realized I might use an audio oscillator, so today I took it out, pulled the chassis (takes 30 seconds - 4 panel thumbscrews and it is out), marvelled at the built. Like a Sherman tank! Beautiful. No criss-crossing at odd angles - everything is north-south grid.

Well, I realized there are two triple electrolytics I would have to take care of, which is easy - it is not a radio so I would just cut them off and put new ones in.

It even has that "no workie-workie when out of the box" button that disconnects power when the chassis is out.

Inside there is also the schematic glued to the back and laquered over, plus the full BOM.

Then I saw no Earth pin in the sawcket, decided to check the chassis for short to the MAINS prongs....woila! One was grounded. Then it occured to me to look at the schematic. And, oh, crappity-crap! It is a hot chassis oscillator! What is worse, the input plug is symmetrical so there is no way to orient it in only one way.

And it does say in the sch "110V DC or AC".

So.....one way of using it is with its own isolation transformer, not shared with anything else.
But I don't feel like taking a risk...what if I forgot one day it needs an isolation!

So.....there it is, a beautiful generator.....semi-useless.
And this is at the very moment I could use one.

Oh, well. I will buy one I guess.

[TA Forbes]

Ahhh, go ahead and use it. What could happen.......??

[morzh]

The death of me could happen.
Then, of course, it will happen one day anyway, and no one knows when.
But myself, I am reluctant to hasten the event.

[codefox1]

There once as an occillator who woudn't set still.

[BrendaAnnD]

Why not install a small isolation transformer inside the unit? Then just add a computer style power connector to the back and ground the middle connection to the frame/chassis.

[TA Forbes]

THAT is an EXCELLENT suggestion, Mike. And you definitely have the electronics G-2 to do it.

I, myself, prefer to connect a wire to the chassis of AC/DC sets that I work on and run it to the pocket I keep one of my hands in when I am working on them.

The hand-in-the-pocket advice is often given by the experts. The wire is my own idea.

Live life on the edge, push the envelope, I always (oops, bzzzz-KA-ZAP) say......

[morzh]

Brenda, as I pointed before, the case is already connected to the negative rectified voltage, so connecting it to the Earth will simply reference the Negative to Earth which is not good at all.

You could probably ask: why not then simply disconnect the case from the Negative? the answer is simple - it is practically military construction and everything is veted/pressed intop the chassis, it is not a simple jumper. It is all across. There is a Negative Common bar running in the middle and it is pressed in the chassis at both ends.

I think the obvious slution is what you and I thought of - the isolation transformer, but the case will have to stay floating.

[BrendaAnnD]

Morzh,

Connecting the case, and therefor the B- line, to ground would not be an issue with the isolation transformer in the equation. It would be the same thing as what happens between the pole pig (transformer on you local power pole) and the HT power lines. Running through the transformer isolates the hot AC voltage. Grounding the case then isolates YOU from becoming a ground.

[morzh]

And this is Earth Ground that protects one in case an isolated internals decided to break down and touch the case from within. The current thus is rerouted to Earth.

Now what happens if I am working with a "hot" equipment which is not isolated via a transformer and then I touch both chassis at the same time?
And what happens if the case is not grounded to Earth?

[BrendaAnnD]

Did you miss the part about installing an isolation transformer inside the equipment? The unit could be operated without an earth ground, but most test equipment now has an earth ground. The problem you mention in your last post would be the same with any modern piece of test equipment. That's why it's always a good idea to isolate any hot chassis equipment you are working on or with.

[morzh]

You are right. I am just not really crazy installing a transformer inside. I forgot how many tubes there are ... I think it says 25W consumption. And it has to be 1:1 transformer.....won't be small. And there are those vertical thick plate shields inside, two I thinkm dividing space in three.

Why didn't they use transformer in the first place....


I used to have a transistor battery-operated audio generator. Long time ago. Should'ove taken it with me here. Took all kinds of stupid stuff....

[BrendaAnnD]

I have several 80VA 1:1 isolation transformers on hand. Not all that large, a bit bigger than a large output transformer. I'll get dimensions off of one, and if it could work for you, I'll be happy to send you one.

[morzh]

Brenda, let me measure my internal space first.
Thing is, I am not sure where I could mount it.
You know what, I will open it, photograph and post it here, then we can see if it is feasible or barely feasible.

[BrendaAnnD]

Morzh,

Here are dimensions and input/output connections for these little isolation transformers.

   

[morzh]

Thanks Brenda, I will try to measure the space later today.