I've been doing some reading on using my scope for troubleshooting.
To avoid destroying the scope, most recommend using an isolation transformer and lifting the ground on the item - e.g. the amp - being tested.
(translation to British: DeviceUnderTest DUT).
It seems to me that lifting the scope ground by running it on an isolation transformer is equally valid, and perhaps more convenient.
What do you do?
Thanks.
To avoid destroying the scope, most recommend using an isolation transformer and lifting the ground on the item - e.g. the amp - being tested.
(translation to British: DeviceUnderTest DUT).
It seems to me that lifting the scope ground by running it on an isolation transformer is equally valid, and perhaps more convenient.
What do you do?
Thanks.
Buy or build a HV differential voltage probe.
Then you can keep everything grounded for safety.
Obviously, I have to do more reading and research!
Thanks!
Though most of what I recall about 'non-standard' scope probes = $$$$
Off to the internet.....
I'm not sure that approach will allow me to probe around inside a tube amp - looking at signal between two points that are 'above' ground potential?
I didn't see 'high voltage' mentioned...
But, my understanding is not deep.
If you need to look at the difference between two points then you need a differential measurement. A dual trace scope should have the a-b function so you just use two probes. You do need HV probes (discussion here somewhere) and I would keep both the scope and the DUT connected to safety ground. Make sure your power connection for this is GFCI protected. Arc fault protection would be a great plus. Leviton AGTR1-W SmartlockPro Dual Function AFCI/GFCI Receptacle, 15 Amp/125V, White - - Amazon.com With the differential input you should not have significant ground loop issues.
Old hot chassis TV's and 5 tube radios are the exception and I would stay clear of those for the most part. Theye were really cheap abominations with the maximum profit motive we still see in cheap stuff.
Old hot chassis TV's and 5 tube radios are the exception and I would stay clear of those for the most part. Theye were really cheap abominations with the maximum profit motive we still see in cheap stuff.
I didn't think of this, until I read it at
Cheap differential scope probe? | Electronics Forum (Circuits, Projects and Microcontrollers)
You can use an isolation transformer on the scope, but beware. If you connect your scope probe ground clip to 300V then 300V will be present on the case of the scope!
And, my older scopes do have metal cases.
That must be the reason that the DUT is the better one to connect to the isolation transformer....
Cheap differential scope probe? | Electronics Forum (Circuits, Projects and Microcontrollers)
You can use an isolation transformer on the scope, but beware. If you connect your scope probe ground clip to 300V then 300V will be present on the case of the scope!
And, my older scopes do have metal cases.
That must be the reason that the DUT is the better one to connect to the isolation transformer....
No products go on the work bench without a pretest of AC power isolation checks.
My work bench and all test equipment are SAFETY GROUNDED. I have several ISOLATION TRANSFORMERS, from 100 watts through 4kw for 120 & 240 volts requirements. My dad taught me that 60 years ago.
I was @ a friend’s place a few years ago when his Tek probe was cremated in smoke & flames. He bought an Isolation transformer after changing his shorts.
Duke
My work bench and all test equipment are SAFETY GROUNDED. I have several ISOLATION TRANSFORMERS, from 100 watts through 4kw for 120 & 240 volts requirements. My dad taught me that 60 years ago.
I was @ a friend’s place a few years ago when his Tek probe was cremated in smoke & flames. He bought an Isolation transformer after changing his shorts.
Duke
OK, so now the chassis of the DUT with all of its exposed metal is at 300V!!
For anything above 50V you should use good HV practices- one hand only keep your distance, make sure you know what you are looking at before you poke around, use probes with little exposed metal on the tip.
For the measurement you are describing I would use a differential measurement. However for most tube work a voltmeter would be fine for looking at voltage differences (e.g. grid bias). Otherwise you would be looking at signal waveforms referenced to ground which should be fine for almost anything.
Here is a simple HV diff amp that can work quite well.
Keep the two input leads close together, or twisted.
Use a ground plane, plastic case, and HV test probe wire for the inputs.
Multiple, series resistors for higher input voltages that exceed the
voltage rating of the input resistors should be used when necessary.
Attachments
Last edited:
No.....
Example - I want to observe the signal between two amp points, one at 300v and one at 350v....amp chassis is not at 300v..
Amp is powered via isolation transformer.
Have I got this incorrect??
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.