I have a workstation with an ESD mat(grounded). I have a power supply, a scope and a soldering station that are grounded (with a 3 prong plug) and a audio generator and a signal generator that are not grounded because of their 2 prong plug (old units). Old radios and amps have 2 prong plugs too...

*** What is the safest way to test radios and tube amplifiers to avoid electric shock?

Sometimes it is useful not to ground a scope (not sure why) and sometimes I measure false voltages with my multimeter (sometimes up to 70V) by touching the probe with my hands or the mat. It worries me a bit.

Do I have to ground all I have and leave them floating?

Thank you

Do I need a isolating transformer?

Isolation transformer would solve a lot of problems, as even if your equipment is ungrounded, there is still a shock risk from the radio to ground, even if AC, as some AC radios have a capacitor that connects the chassis to the line cord, and there is always capacitive and leakage coupling through the transformer.

As I am too lazy/stubborn to purchase an isolation transformer, I see to it that all of my test equipment is ungrounded, as if it were grounded and you connected it to a live chassis, BAM! ...You'd have a small surprise. I always remember, though, that even if the equipment has a transformer, and is ungrounded, there still exists capacitive coupling and leakage coupling, especially on humid days, so I always remember to never ever touch two pieces of equipment at the same time while they are plugged in. That also means that when connecting your signal generator to a radio, don't hold both the radio and the generator wires at the same time. Isolation transformers, I believe, have their windings wound on separate spools, and typically modern spools are made of plastic, so there is a very small chance, if any, that there will be any significant capacitive or resistive leakage between the windings, but it's still a good idea to be cautious when dealing with your life.

I also make it a practice to not handle and work on equipment while standing barefoot on concrete or other conductive surfaces. Typically hardwood and carpet don't pose a shock hazard, and the same for varnished wooden chairs. However, on very humid days, I used to occasionally receive a very nasty shock from my portable kiddy phonograph when I'd touch the tone arm while sitting on carpet. This explains why, when my mother handed it down to me from her, the tone arm was fitted with a Band-Aid. I didn't like the looks of the Band-Aid, so I removed it.

T.

Hi Jeffy

If you work on AC/DC radios it's best to use an isolation transformer. Especially if your soldering iron and equipment is grounded. Since these radio operate right off the AC line you may accidently solder or use other grounded equipment and get a flash...

By the way an ESD mat was originally for handling semiconductors. Won't hurt working with tube equipment. Most are soft rubber and will be easy on the feet...

Others may not say this but I remove grounds to my soldering irons and scopes. I may leave an AC/DC radio plugged into AC line. I don't want a flash.

Grounds are often removed on scope AC cords to prevent loops. Best to ground the scope probe right near signal input. If you use AC cord ground might have false pulses.

Norm

:I have a workstation with an ESD mat(grounded). I have a power supply, a scope and a soldering station that are grounded (with a 3 prong plug) and a audio generator and a signal generator that are not grounded because of their 2 prong plug (old units). Old radios and amps have 2 prong plugs too...
:
: *** What is the safest way to test radios and tube amplifiers to avoid electric shock?
:
:Sometimes it is useful not to ground a scope (not sure why) and sometimes I measure false voltages with my multimeter (sometimes up to 70V) by touching the probe with my hands or the mat. It worries me a bit.
:
:Do I have to ground all I have and leave them floating?
:
:Thank you
:

:I have a workstation with an ESD mat(grounded). I have a power supply, a scope and a soldering station that are grounded (with a 3 prong plug) and a audio generator and a signal generator that are not grounded because of their 2 prong plug (old units). Old radios and amps have 2 prong plugs too...
:
: *** What is the safest way to test radios and tube amplifiers to avoid electric shock?
:
:Sometimes it is useful not to ground a scope (not sure why) and sometimes I measure false voltages with my multimeter (sometimes up to 70V) by touching the probe with my hands or the mat. It worries me a bit.
:
:Do I have to ground all I have and leave them floating?
:
:Thank you

Jeffy:
You might consider putting a Ground Fault Circuit Interrupter (GFCI) in the outlet feeding your workbench. This is a device that monitors the current leaving the wall and coming back to the wall, and if the currents aren't just about Exactly the same, will trip the AC. Quickly, so you don't even feel a shock. They're required on hairdryers now, and the whole wall outlet device can be bought at a home improvement store of most any sort. Less than ten bucks in my area.
Lewis

Isolation transformer is best. No matter what I do, I get my gnarly old hands the hell out of there before I fire the set up. I installed insulated alligator clips on the ends of my test probes, and still don't trust the insulation. (What if it is a humid day and you perspire?)

And don't bet your life on a transformer set. Death caps or not.

::I have a workstation with an ESD mat(grounded). I have a power supply, a scope and a soldering station that are grounded (with a 3 prong plug) and a audio generator and a signal generator that are not grounded because of their 2 prong plug (old units). Old radios and amps have 2 prong plugs too...
::
:: *** What is the safest way to test radios and tube amplifiers to avoid electric shock?
::
::Sometimes it is useful not to ground a scope (not sure why) and sometimes I measure false voltages with my multimeter (sometimes up to 70V) by touching the probe with my hands or the mat. It worries me a bit.
::
::Do I have to ground all I have and leave them floating?
::
::Thank you
:
:
:Jeffy:
:You might consider putting a Ground Fault Circuit Interrupter (GFCI) in the outlet feeding your workbench. This is a device that monitors the current leaving the wall and coming back to the wall, and if the currents aren't just about Exactly the same, will trip the AC. Quickly, so you don't even feel a shock. They're required on hairdryers now, and the whole wall outlet device can be bought at a home improvement store of most any sort. Less than ten bucks in my area.
:Lewis
:
:

An isolation transformer is the best investment for working on any electronic gear. You never want to be part of the ground return. Touching a hot chassis while connection a grounded lead can be a shocking experience.

:An isolation transformer is the best investment for working on any electronic gear. You never want to be part of the ground return. Touching a hot chassis while connection a grounded lead can be a shocking experience.
:
So if you use a isolation transformer on just old radio.. connecting test equipment that has grounded plug not connected to transformer just connect to wall outlet ,,,should be ok

::An isolation transformer is the best investment for working on any electronic gear. You never want to be part of the ground return. Touching a hot chassis while connection a grounded lead can be a shocking experience.
::
:So if you use a isolation transformer on just old radio.. connecting test equipment that has grounded plug not connected to transformer just connect to wall outlet ,,,should be ok
: