Author Topic: cheap tek 500MHz passive probes on ebay. can they be used on any scope?  (Read 7693 times)

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Offline JPortici

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this auction, that might interest somebody
http://www.ebay.it/itm/TEKTRONIX-P6139A-Oscilloscope-Passive-Probe-/282176061341?hash=item41b300ff9d:g:tv0AAOSwmLlX2QcD

seemed a bargain.

i bought one to try if it is any good, but i have no idea if it needs a tektronix scope with readout system to work.
does it, or i can use it with whatever scope as a simple probe?
 

Online PA0PBZ

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #1 on: September 16, 2016, 11:45:47 am »
Look at the compensation range of the probe (8 to 18 pF in this case) and make sure that the scope you want to use has an input in this range.
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Online TimFox

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #2 on: September 16, 2016, 03:40:34 pm »
Typically, the capacitance at the CRO input is stated on the panel, near the BNC input.
 

Offline Keysight DanielBogdanoff

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #3 on: September 16, 2016, 03:51:29 pm »
The sense resistor values that scopes use to determine attenuation settings are typically standardized across manufacturers. Like PA0PBZ said, you'll want to check the compensation range and make sure they're compatible.

Active probes are a different story.
 

Offline dav

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #4 on: September 16, 2016, 04:49:39 pm »
So does it work on a Agilent/Keysight DSOX3054X series scope?
 

Offline TheSteve

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #5 on: September 16, 2016, 04:52:30 pm »
So does it work on a Agilent/Keysight DSOX3054X series scope?

Yes they should work and auto detect 10x properly.
VE7FM
 

Offline dav

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #6 on: September 16, 2016, 05:00:26 pm »
On DSOX3054 front panel I can read:
1 Mohm  15pF


P6139A probe:
10 Mohm 8pF
compensation range: 8pF to 18pF

So is it ok? (no matter about the 10 Mohm input impedance?)
 

Offline TheSteve

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #7 on: September 16, 2016, 05:04:49 pm »
On DSOX3054 front panel I can read:
1 Mohm  15pF


P6139A probe:
10 Mohm 8pF
compensation range: 8pF to 18pF

So is it ok? (no matter about the 10 Mohm input impedance?)

Yes, it will compensate just fine.
VE7FM
 

Offline dav

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #8 on: September 16, 2016, 05:08:49 pm »
 

Offline rf-loop

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #9 on: September 17, 2016, 09:07:55 am »
On DSOX3054 front panel I can read:
1 Mohm  15pF


P6139A probe:
10 Mohm 8pF
compensation range: 8pF to 18pF

So is it ok? (no matter about the 10 Mohm input impedance?)

Scope input BNC  1Mohm 15pF (+ something)

Probe (low frequency) compensation range 8pF - 18pF.  (this is for scope input capacitance)

This probe tip parameters are  10 Mohm 8pF.
This have nothing to do with this matching with scope input.

So, yes, low frequency compansation range is ok for this scope input.


Sidenote:
when you measure some circuit,  mostly you can forget this 10Mohm.
But do not forget in RF circuits that you connect 8pF capacitor in circuit.
Yes better than 20pF or 16pF but still 8pF is LOT of in many cases.
@500MHz it have 39.8 ohm reactance, not 10Mohm what is DC resistance.








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Online tggzzz

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #10 on: September 17, 2016, 09:59:52 am »
But do not forget in RF circuits that you connect 8pF capacitor in circuit.
Yes better than 20pF or 16pF but still 8pF is LOT of in many cases.
@500MHz it have 39.8 ohm reactance, not 10Mohm what is DC resistance.

Very true.

It is also worth pointing out to beginners the effect the ground lead will have; a 6" ground lead will be about 140nH, and that will resonate with the tip capacitance at ~100MHz.

I've managed to reduce that inductance by copying techniques used in HP probes. FFI see https://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/

EDIT: updated results at higher frequencies at https://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/
« Last Edit: September 17, 2016, 04:54:39 pm by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline JPortici

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #11 on: September 17, 2016, 05:29:33 pm »
 :clap:

love me dat blue phosphor
 

Online tggzzz

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #12 on: September 17, 2016, 06:01:09 pm »
:clap:

love me dat blue phosphor

Tek 485s are sweet little scopes in more ways than one!

There's a working one for sale on fleabay at the moment (no affiliation): http://www.ebay.co.uk/itm/Tektronix-485-two-channel-350MHz-analogue-oscilloscope-/282171555562
20 hours left :)
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline JPortici

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #13 on: September 17, 2016, 06:13:49 pm »
too bad my money is constantly feeding my 7k addiction!
 

Offline David Hess

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #14 on: September 17, 2016, 09:08:36 pm »
When you get somewhere above 200 MHz with high impedance passive probes, the high frequency transient response of the probe is matched to the oscilloscope input so not all 500 MHz probes will deliver optimal response with all 500 MHz inputs.  You can see this in the old Tektronix probe recommendation guides where specific probes are recommended for specific oscilloscopes and "A" or "B" revision probes will be recommended for later oscilloscopes of similar or equal bandwidth.

High bandwidth general purpose probes have 2 or 3 user accessible high frequency adjustments besides the compensation adjustment so with a suitable signal source, they can be adjusted to work with any high bandwidth oscilloscope input.

Most people do not have a suitable signal source so not only will they not be able to adjust such a probe, they also will not be able to verify that a more specific probe is not working correctly and in most cases, the differences are not going to matter because the effect of the probe's input impedance will affect the signal that much anyway.  The probe and oscilloscope specifications depend on an unrealistic 25 ohm source impedance but the designers had to pick something as an objective reference.
 

Online tggzzz

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #15 on: September 17, 2016, 09:32:35 pm »
All valid points.

I did tweak all the HF adjustments in the Tek probe, unsurprisingly.

I'm content if beginners merely realise that morning technique significantly affects the waveforms, how to recognise some effects, and some of the measures that can be taken to minimise the consequences.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline KE5FX

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #16 on: September 18, 2016, 06:19:32 am »
Watch out with the P6139A probe.  Unless they've had their cables replaced, they had a whisker- or dendrite-growth problem in the cable that will short out the signal and drive you nuts.  It can be cleared by running some current through the BNC connector but only temporarily.  The only fix is to order a new cable from Tektronix, which I'm not sure you can still do.
 
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Online tggzzz

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #17 on: September 18, 2016, 07:32:16 am »
Watch out with the P6139A probe.  Unless they've had their cables replaced, they had a whisker- or dendrite-growth problem in the cable that will short out the signal and drive you nuts.  It can be cleared by running some current through the BNC connector but only temporarily.  The only fix is to order a new cable from Tektronix, which I'm not sure you can still do.

Interesting!

Have you considered adding that to http://w140.com/tekwiki/wiki/p6139 ?
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
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Offline KE5FX

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #18 on: September 18, 2016, 07:56:50 am »
Watch out with the P6139A probe.  Unless they've had their cables replaced, they had a whisker- or dendrite-growth problem in the cable that will short out the signal and drive you nuts.  It can be cleared by running some current through the BNC connector but only temporarily.  The only fix is to order a new cable from Tektronix, which I'm not sure you can still do.

Interesting!

Have you considered adding that to http://w140.com/tekwiki/wiki/p6139 ?

Agreed, could be worthwhile when I have time to sign up for an account on there.  It's not clear how widespread the problem is, or what serial #s are affected, but the problem is real enough.  It's bitten me and at least a couple of other people who got their probes from different sources at different times.  Very frustrating, because they are otherwise nice probes.
 

Offline JPortici

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #19 on: September 19, 2016, 05:03:02 pm »
Interesting.
Anyway, mine arrived today. Seems to be working. The probe interface talks to my TEK7704A and informs the readout system that this is a 10x probe.
Thanks to tolerances, the capacitance is just enough so i can compensate the probe on a 7A22 7A26 (1M, 22pF)
Unfortunately i don't have faster plugins at the moment.. and IIRC they all are 50 ohm input.
The fastest signal i have around here is still the 2ns rise time trigger output from another scope and probing it is consistent with what i get using directly a (terminated) piece of coax.
the accessories in the pouch will be put in use very soon.
Not bad for 50 euro total :)

« Last Edit: September 19, 2016, 07:40:39 pm by JPortici »
 

Online tggzzz

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #20 on: September 19, 2016, 05:11:30 pm »
Watch out with the P6139A probe.  Unless they've had their cables replaced, they had a whisker- or dendrite-growth problem in the cable that will short out the signal and drive you nuts.  It can be cleared by running some current through the BNC connector but only temporarily.  The only fix is to order a new cable from Tektronix, which I'm not sure you can still do.

Interesting!

Have you considered adding that to http://w140.com/tekwiki/wiki/p6139 ?

Agreed, could be worthwhile when I have time to sign up for an account on there.  It's not clear how widespread the problem is, or what serial #s are affected, but the problem is real enough.  It's bitten me and at least a couple of other people who got their probes from different sources at different times.  Very frustrating, because they are otherwise nice probes.

It all sounds vaguely similar to the known problem with the delay line in HP1740A scopes. There, if you notice the risetime has risen from 3.5ns to 7ns, don't bother to tweak the controls as stated in the service manual. Instead, get your hand deep into the scope, and simply fondle, massage and squeeze the delay line.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline David Hess

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #21 on: September 19, 2016, 05:31:50 pm »
Thanks to tolerances, the capacitance is just enough so i can compensate the probe on a 7A22 (1M, 22pF)

The 7A22 is 1M and 47pF.  My common 100 MHz x1/x10 probes are only rated to about 33pF but barely make it to 47pF.  My faster 250 MHz x10 probes do not have enough range to work with a 47pF input.

Quote
Unfortunately i don't have faster plugins at the moment.. and IIRC they all are 50 ohm input.

The fastest common high impedance amplifier is the 7A26 dual trace at 200 MHz.  The single trace 7A16A is 225 MHz.  The four trace 7A42 is 350 MHz.

Above 200 MHz, 50 ohm inputs are not that much of a disadvantage because the capacitance at the tip of a high impedance probe is a significant limitation at high frequencies.  A x10 or x100 50 ohm probe has a higher input impedance at high frequencies although not at DC.
 

Offline JPortici

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #22 on: September 19, 2016, 07:40:12 pm »
7A26, sorry! i tested with a 7A26
 

Online MarkL

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #23 on: September 20, 2016, 02:33:25 pm »
These are nice probes.  I have a set of 4 myself.

The only thing I would add to what's already been said is that the tips are rather delicate.  I've broken several.  And not the metal tip itself.  The plastic that holds the tip can crack or become loose and then the tip falls out.  I think I was not being careful enough putting on the sprung hook or rotating the hook too much.

The tips alone are not replaceable.  They come as a cartridge along with the input resistor and are expensive (qty 1 $45 at testpath.com, for example).
 

Offline JPortici

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Re: cheap tek 500MHz passive probes on ebay. can they be used on any scope?
« Reply #24 on: September 20, 2016, 06:30:56 pm »
These probes are sold for 45. Grab some :D i will if there are more
(The seller contacted me before to ask how they were going. I'm not sure how to interpret that ::D)
 


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