Isolation Transformer

[JoeTele]

Hi,

I'd like to have an isolation transformer when I'm working on amps. Thing is, they seem to be advertised for different purposes, such as noise reduction and surge protection, and I've gathered (correctly or not) that not all of them have the precise grounding associated with the added layer of safety in electrical testing. Are there any giveaways as to which will perform the desired function. I've been looking at one called the Tenma 72-6670A for about $100 (450VA, 3.75 amps) but a tech support person told me that the only "safety" it provided was minimizing shock and voltages, and did not seem keen on touting it for working on electronic circuits. Perhaps this was just for liability purposes? Tripp lite isolator models seem to be pretty prominent too and some of those look to be in my price range ($100-$150). Any guidance would be appreciated.

Thanks!

Joe

[Structo]

Are you going to use a isolation transformer to work on transformer-less amplifiers or radios?

[Reeltarded]

For your safety, or the circuit's safety?

I think you might be looking for something that doesn't exist.

[JoeTele]

Nothing transformerless. The kind of isolation transformer that is supposed to reduce the risk of me becoming a path to ground.

Joe

[Reeltarded]

You are searching for something that does not, cannot, and will not ever exist.

[JoeTele]

Ok, but if you could just address the following it would be great.

Here is one explanation from a physics forum:

The short answer is that most electric shocks do not occur because someone simultaneously touches two supply wires, rather they more frequently occur when someone touches a single live wire and a "ground". The isolation transformer has a secondary which is non-grounded, thus you can avoid being shocked by touching just one wire and "ground".

Reference https://www.physicsforums.com/threads/i ... ty.265143/

And this from Wikipedia:

In electronics testing and servicing an isolation transformer is a 1:1 (under load) power transformer used for safety. Without it, exposed live metal in a device under test is at a hazardous voltage relative to grounded objects such as a heating radiator or oscilloscope ground lead (a particular hazard with some old vacuum-tube equipment with live chassis). With the transformer, as there is no conductive connection between transformer secondary and earth, there is no danger in touching a live part of the circuit while another part of the body is earthed.

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I know these are not authoritative, but is what is being described here something different from what I'm asking for?

Thanks!

Joe

[Reeltarded]

No, I won't. It's beyond me. I work safely and I don't get killed. I use power conditioning extensively elsewhere in audio production..

If you become the highest potential ground, you will be the highest potential ground.

Not only do i not get it, i am not interested in getting it.

[Ron Worley]

Sencore PR57.

[JazzGuitarGimp]

Isolation transformers won't do what you are expecting with regards to tube amps. Here's why: the chassis for all tube amps I've ever encountered is used for the B- (GND) connection. So even if you float the chassis from earth ground, you will still get zapped if you touch both the chassis and a B+ connection. Since all modern day amps use a built-in (isolation) transformer, you would actually achieve the same end result by using a two-prong to three-prong adaptor, and not connecting the green pigtail coming out of it. Now you have broken the connection from earth ground to the chassis of the amp. But again, this buys you nothing with a tube amp since the piwer supply minus connection is connected to the chassis.

Best advice? Keep one hand in your pocket while probing around in a live chassis.

[JoeTele]

Thanks for the clarification! I guess the scenario I was envisioning was having one hand in my pocket (always) and touching a live wire, with the current going from that wire to my floor through me. That was what I was wanting to protect against.

In any case, I'll follow your advice and perhaps upgrade some parts for my latest build with the money I won't be spending on the IT.

Thanks again!

Joe

[Long Distance Call]

If you are concerned with current going to the floor through you, consider getting a 1" thick rubber shop mat to stand on. Works great...

Cheers,
LDC

[gui_tarzan]

While the advice previously mentioned is good, the best advice I can think of is to know where the high voltage is and don't touch it with your bare hands once it has been charged or is turned on. Discharge the filter caps before you do any work inside and you'll be fine and never, ever put your fingers in there while it's on. Use a non-conductive probe for tapping on wires and parts when you're troubleshooting and I use clip-ends on my meter probes so they don't slip when I'm checking voltages.

[Reeltarded]

also.. plastic is not non-conductive in all circumstances... so..

If you probe a running amp at every point for voltages, you will find out where no man can go. If you discharge a 50u/450v cap at 98v with your right elbow you will find out your drain has come loose.

I know this.

[JoeTele]

Thanks for all of the tips! I've got a wooden probe for "chopsticking" and a discharge tool which I employ regularly, always use alligator clips for the ground connection of my meter, o-scope, etc (and make sure it is mechanically secure) and have electrical-taped off all but about the first 1/8 inch or so of my main meter probe to minimize the possibility creating a short with that, and plan to start keeping a second meter on the first filter cap at all times. I also variac up slowly after any significant mod and often have a kill-a-watt behind that to keep an eye on current, especially when bringing up a new build (where I adhere to the processes of Paul Ruby and others). I know they're not the be-all/end-all, and there isn't complete agreement on their effectiveness, but I'll also likely add electrical safety gloves (actually a [single] glove, adhering to the one-hand rule) and gfci, as I figure they can't hurt.

Thanks again. It's great that this help is out there for the self-taught (and others) among us!

Joe

[Leo_Gnardo]

I'll also likely add electrical safety gloves (actually a [single] glove, adhering to the one-hand rule)

All good! And with the glove you'll be the Michael Jackson of tube amps, put some rhinestones on it. At least you'll avoid doing a shock-induced moon walk.

Truth be told I've never seen anyone wearing safety gloves to work on amps. OTOH I'm aware of "white glove" repair garages that cater to rich folks with fancy collector item cars, and charge heart-surgery prices. You could develop a mystique and a following, make yourself a fortune. Heyyy, I oughta do that.