High Voltage Testing

[Peter S]

Hi Folks, I am doing some fiddling around on tube amplifiers, guitar amps mostly. I'm using a Leader LBO 516 old-school CRT screen scope. It specs max input voltage 400 V ( AC + DC ). As you know, many tube amps have B+ voltages higher than this. I have a 10:1 probe but doubt very much that I'm now safe up to 4000 Volts!
I have not seen any spec for the max Voltage for this probe. Would this probe be safe for 450 Volt enviroments?

 

[Gepetto]

Hi Folks, I am doing some fiddling around on tube amplifiers, guitar amps mostly. I'm using a Leader LBO 516 old-school CRT screen scope. It specs max input voltage 400 V ( AC + DC ). As you know, many tube amps have B+ voltages higher than this. I have a 10:1 probe but doubt very much that I'm now safe up to 4000 Volts!
I have not seen any spec for the max Voltage for this probe. Would this probe be safe for 450 Volt enviroments?

No. The scope limits you to 400v max

 

[Peter S]

Thanks, Joe. Always stubborn, so something like this would not be safe to use?
https://www.amazon.ca/P4250-Oscilloscope-Probe-High-Voltage-100/dp/B07QM6MTHW

 

[George S.]

You are using a isolation transformer on the DUT?

 

[Gepetto]

It is your scope Peter, I never exceed the limits of mine which states 300Vrms or 450VDC

There are usually cautions as well if you intend to float the reference (the scope ground lead) with respect to safety ground.

Mine has a limit of 30V of float above safety ground. I would have to defeat the safety ground to go above that.

Your scope user manual usually provides guidance of what you can and cannot do.

 

[Peter S]

Thanks again. I'm am very 'attached' to my old Leader scope, so I won't risk it with the questionable quality of that probe. As far as isolation for the DUT, most guitar amps have power transformers so they are isolated from the line. I have had a few amps with no power transformer so their B+ is much less than 400 V.
Regarding float above safety ground; I better do some research in the manual, I have an IEC cord for the scope with the ground pin removed, just to avoid ground loops...was my thinking. I always tie the scope ground to the DUT of course.