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100:1 probe for measuring ripple in a tube amp power supply
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Andreax1985:
Hi, I wish to measure b+ ripple in a tube amp. Since the b+ rails are at 350V, I was considering buying a 100:1 passive probe for my scope (rated for 400V input). Nevertheless, here is my doubt: I'll need to use the scope in AC coupling mode to clearly see the ripple. This means that I cannot safely use a cheap 100Mohm 100:1 probe. I'm on a budget and I can't afford a differential probe. Could you suggest me a suitable 100:1 probe which does not give issues when used in AC coupling mode?
Richard Crowley:
It is not clear whether you are saying that your (unidentified) scope already has AC mode, or whether you think you need a new probe to get AC coupling?

Ripple is typically a very small signal.  Using a 100x probe will probably make the ripple nearly invisible.

You don't need a 100x probe unless you are trying to measure a very large signal (350V).  But you are not asking about measuring the 350V. That should be measured with a DMM.  You are asking about measuring the ripple which is a very small AC component resting on top of the 350V.  You need a 1x or 10x probe with AC coupling.
Andreax1985:

--- Quote from: Richard Crowley on January 28, 2019, 03:19:24 pm ---It is not clear whether you are saying that your (unidentified) scope already has AC mode, or whether you think you need a new probe to get AC coupling?

Ripple is typically a very small signal.  Using a 100x probe will probably make the ripple nearly invisible.

You don't need a 100x probe unless you are trying to measure a very large signal (350V).  But you are not asking about measuring the 350V. That should be measured with a DMM.  You are asking about measuring the ripple which is a very small AC component resting on top of the 350V.  You need a 1x or 10x probe with AC coupling.

--- End quote ---

My scope has AC coupling mode. As I said, I want to visualize ripple in the (high voltage) b+ stage of a tube amp (350V+). Of course the ripple component will (hopefully) be very small compared to the signal, but I think you are well aware that in AC coupling mode the DC component is not attenuated at all. So, if I use a cheap 100:1 passive probe for probing a 350+ V rectified signal in AC coupling mode I have good chances of damaging the scope. Hence, my question.
Martin.M:
you can use a Tektronix P6006 Probe from flea market , 10:1 , <600V  :)
It is build for glowing scopes but useful with any 1M input BNC
Martin
Andreax1985:

--- Quote from: Martin.M on January 28, 2019, 03:29:19 pm ---you can use a Tektronix P6006 Probe from flea market , 10:1 , <600V  :)
It is build for glowing scopes but useful with any 1M input BNC
Martin

--- End quote ---

I already have 10:1 probes (CAT I, 600V), but perhaps I'm not being clear enough on what I think the problem is...
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