Bottlehead Forum
General Category => Tech Tools => Topic started by: Downhome Upstate on July 16, 2014, 04:21:57 PM
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Just picked this unit up today w/no probes. The 'scope's front end warns not to exceed 400 v pk. I'm looking for a pair of probes that will allow measurement of tube PSU B+ voltages and power transformer secondaries. Do I just need a decent generic replacement voltage probe with x100 attenuation, and another pair of x1 and x10 for the low voltage work?
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I have the same model, probes shipped with the kit are 10x, part number p6103. I also have a 1x probe, part number P6062B. All of mine i sourced from eBay and i suspect they are of higher quality than the generic eBay ones.
I wouldn't mind some clarification on the voltages too, i was under the impression the with a x10 probe a 100v supply would only be sending 10v to the scope.
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[quote i was under the impression the with a x10 probe a 100v supply would only be sending 10v to the scope.
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That is true...John
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The working voltage of the x10 (or convertible x1 to x10) probes that I've seen seems to top out at somewhere between 300v and 600 v. Reading across both secondaries of the center-tapped PA060 pwr transformer on my ST70 project would give 720v. Looks like the x100 probes tend to be rated for 1 to 2 KV. (I don't know what happens when you exceed the voltage rating of a probe.)
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You can buy good 10:1 scope probes from MCM Electronics. I did when I got my Tek.
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The working voltage of the x10 (or convertible x1 to x10) probes that I've seen seems to top out at somewhere between 300v and 600 v. Reading across both secondaries of the center-tapped PA060 pwr transformer on my ST70 project would give 720v. Looks like the x100 probes tend to be rated for 1 to 2 KV. (I don't know what happens when you exceed the voltage rating of a probe.)
In that case wouldn't you be using two probes grounded to the center tap, so each probe will only be measuring ~310v?
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You can buy good 10:1 scope probes from MCM Electronics. I did when I got my Tek.
Grainger,
Is yours by Tenma (sold by MCM)?
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I don't remember. It was around 1994 when I bought them.
I called them and gave them the model number. They suggested a pair of probes for under $50.
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I wound up going with 2 different (single) probes from Test Products Int'l ("TPI"). A model P250 x100 non-switchable passive probe rated at 1500 v for $45, and a model SP100B switchable 1x/10x passive probe rated at 150/300 v for $40, both from Digi-Key.
I called TPI before deciding to buy these, and mentioned to one of their tech reps that some vendors show TPI's 1x/10x passive probes being rated at 600v. (You can see the same thing on the web with other x10 probes, marketed under different names.) He replied that the 150/300 v values on their website were correct (the same or similar ratings as published by Tektronix, Pomona and others for x10 probes, BTW) and that TPI tries to get retailers to list the correct (lower) working voltage of their probes. He also said that there are only a few manufacturers of oscilloscope probes, and that the difference in price between the passive probes sold under different names is basically a marketing decision.
Now I just have to remember which probe is which before picking [it] up and measuring high voltage.