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Old 4th October 2009, 03:42 PM   #1
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Default x1 Oscilloscope probes

Hello forum members.

I am a fellow hobbiest and have a Tek 465B two channel scope I use for my amplifier work. I am in need of buying a x1 probe for this scope and have been searching the Ebay and Google for a probe to purchase. There is very few opportunities on Ebay for a x1 probe that has a working voltage rating of 600V. I have found a few after market low cost probes on Google for approx. $20.00 to $40.00 but I have no idea which one is a good one or which maybe a poor one. I am wanting this probe to make ripple measurements and thought this might be a good opportunity to ask fellow forum members if they have previous experience of buying after market probes for Tek scopes. Thus, I would appreciate anyones recommendations of where to purchase a probe from (in the USA) and any particular models people may have experience with.

Thanks,

DMSpike (aka Doug S.)
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Old 4th October 2009, 05:30 PM   #2
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The 465 is only rated for 250VDC input (500V when AC coupled), so there's no point in getting a 1X probe rated higher... the 10X probe can give a higher input rating.
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Old 4th October 2009, 05:36 PM   #3
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For making high voltage ripple measurements you need to be careful. The 1X probe voltage rating is one concern but you have to watch the scopes maximum input voltage also. My recommendation for making high voltage AC measurements is to use a high voltage film cap between the probe and the circuit to be measured. By blocking the high voltage DC component of the signal to be measured you greatly reduce the stress on the probe and scope input.

When making measurements with a external blocking capacitor you MUST have the scope in DC coupling! Otherwise you will be putting the scope's input capacitor in series with the external blocking cap with the DC voltage split between the external capacitor and the internal capacitor.

In the past I have setup input blocking caps made from Axial lead film caps that the probe clips into. This allows you to probe a circuit much the same way you do with a standard probe. One end of the cap gets cut off ~.5" from the cap body to be the probe end. The other lead gets a tight "Z" bend 1/4 inch out from the body with the center of the "Z" being ~1/16" wide. Clip your probe tip on the center of the "Z". Take the remaining long part of the cap lead and wind it around the probe tip 2 or 3 times. Winding the cap lead around the probe tip keeps the cap aligned with the probe.

Remember that when you are using an external DC blocking cap you have to discharge the cap after making measurements. Just touch the cap to ground and hold until the scope trace comes back to 0V.

We used this probing scheme while working on scopes when making AC measurements in DC restorer circuits that were elevated in the 2KV to 3KV range.
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Old 5th October 2009, 12:03 AM   #4
jjman is offline jjman  United States
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I've purchased 1x, 10x, and 100x probes on ebay for my Tek 2246. A 10x works well in almost all cases for me. Although I need to use a 1x when scoping 3+ channels since the 3 & 4 channels have limited amplitude ranges. And if the 10x probe has the pin on the bnc ("coded") the scope adjusts the display and you don't have to do any math in your head. (I don't know if your model scope has that capability.) Only the Tek branded probes have the pin (and only some of them) AFAIK. A 10x also allows you to cheat on the max voltage that the scope will see by a factor of 10 making it kosher for most any tube amp use. The probe itself has a voltage rating which I think is related to the gauge of the probe's wire.

As far as 1x Tek brand I've seen these models:

P6011
P6028
P6101, A, B

Seems to me that the vast majority of the Tek brand probes are 10x.
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Old 5th October 2009, 01:06 AM   #5
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Hello Tom, Gary and JJman,

Thanks for the good feedback and all of your points are well taken. I currently have plenty of good Tek 10x probes and none of mine have x1 capability. Yes, my scope does have the pin driven automated 10x correction on the vertical amplifier inputs. I mainly asked about the 600v probes as most of the after market ones I have seen are either 250v or 600v rated. If I am going to purchase one and have a choice, I will go with the higher rated breakdown. Gary's comment of using a film cap in series and running the scope DC coupled if measuring something in excess of 250v is a good way to assure protection for the vertical amplifier input and I will certainly take advantage of that when I want to measure high tension ripple accurately in excess of the 250v level.

As I said at the beginning, thanks for the feedback. I am still looking for recommendations on after market probes.

DM Spike (aka Doug S.)
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