Variac as isolation transformer?

Almost certainly not. With very few exceptions, variacs are auto-transformers (a single winding with a common end).

No.

John

No, and that isn't a design question.

You really ought to be asking yourself why you think a variac is an isolation transformer. And start with understanding what a variac is, and what an isolation transformer is. Then, you can answer your own question.

Michael

Homework ??

What professor, these days, would ever have heard of a variac?

John

I have seen an isolated Variac, but only one. All the rest were a single winding that functioned like an inductive version of a potentiometer.

The old ones who haven't quite hit retirement yet?

I know a professor who -- in his undergraduate transmission lines lab -- still has kids using an ancient tube-based TDR with those "flared blade" style WW II-era RF connectors on it, and I'm sure he knows what a VARIAC is.

Although he might not know the proper name of those connectors, just as I don't. :-) (Interesting, they do appear at ham fests every now and again, but I haven't every seen them at a commercial trade show... hmm...)

I own one, and it's one of those generic Chinese-made brands that you see advertised in, e.g., Nuts & Volts. They're only a skosh more expensive than the traditional kind.

I haven't seen high-powered isolated VARIACs, though... mine is only something like 300W.

Flared Blade? So thats what those things are called. I have a 10X 20 dB attenuator in the middle betwee two sets of BNC adaptors. I'll call it Flared Blade to BNC and so on. The pieces are General Radio GR874

I do have a nice Staco variac with meters and optional isolation ouput. i sometimes use that in conjection with my series light bulb box with switches for 40, 140, and

240 watts.

greg

Anyone who has read Terman and Petit?

Are you talking about the General Radio 874 Hermaphroditic connectors?

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Michael A. Terrell
Central Florida

Dunno. You should be able to figure this out by unplugging it from the wall and using an ohmmeter from input to output.

I think the congenital "Variac" has a hard time being an isolation transformer, as it's usually just a single winding on a toroid core, tapped off as an autotransformer.

BUT a faint memory is that there's some other manufacturer that DOES provide variable voltage and isolation on one core. Here's one recent one:

Tek 1S2, likely. I have a few, and they're cool.

GR874 connectors.

John

Hi Michael,

Why yes, I think I am; thanks for the real number... I'm sure I'll forget it within weeks, but at least now Google news will remember for me!

The students (and I) were always impressed with the nifty electrostatic paper holder on the Tek pen plotter that it's connected to. Magic!

Since you have a 1S2... one of the blades is broken off on the signal input/output connector. Any chance of repairing it? The connector seemed like an integrated part of some "sampling head" kind of module inside; not just a connector that transitioned to, e.g., a coax cable.

---Joel

You'd have to take it apart, but that's not bad. The unisex connector pin should be a standard GR part. I have a lot of old GR bits and pieces. If you take it apart and photograph things, I bet I could find something around here that would work. I also have several broken

1S2's, so I could donate one for parts. One working TDR is better than two dead ones.

I started learning picosecond electronics with a 1S2 plugged into a

547. The 1S2 is a 25 ps pulse generator and a 4 GHz scope, all in one little box.

Nowadays I'm using mostly Tek 11801 series scopes with the SD24 TDR head, all from ebay... nice rig, very precise and quantitative, interfacable to a PC, fairly cheap.

If you hack a 50 ohm microstrip from a piece of copperclad, and TDR it, and run your finger along the line, people get amazed. The equivalent sweep speed is multiples of c.

John

I thought they were known as GR style connectors.

M Walter

Win Hill? ;-)

Cheers! Rich

My, there's a hundred of the things scattered throughout the rather small Physics Department at Beloit!

Bunch of tubed equipment too, for that matter. Most of it is sitting in the basement though.

Tim

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