cheap tek 500MHz passive probes on ebay. can they be used on any scope? - Page 1
Forum section: electronics / testgear

author: JPortici
author_rank: Super Contributor
timestamp: September 16, 2016, 11:15:42 am
content: this auction, that might interest somebodyhttp://www.ebay.it/itm/TEKTRONIX-P6139A-Oscilloscope-Passive-Probe-/282176061341?hash=item41b300ff9d:g:tv0AAOSwmLlX2QcDseemed 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?

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 16, 2016, 11:45:47 am
content: 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.

author: TimFox
author_rank: Super Contributor
timestamp: September 16, 2016, 03:40:34 pm
content: Typically, the capacitance at the CRO input is stated on the panel, near the BNC input.

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: September 16, 2016, 03:51:29 pm
content: 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.

author: dav
author_rank: Regular Contributor
timestamp: September 16, 2016, 04:49:39 pm
content: So does it work on a Agilent/Keysight DSOX3054X series scope?

author: TheSteve
author_rank: Unknown
timestamp: September 16, 2016, 04:52:30 pm
content: Quote from: dav on September 16, 2016, 04:49:39 pmYes they should work and auto detect 10x properly.

author: dav
author_rank: Regular Contributor
timestamp: September 16, 2016, 05:00:26 pm
content: On DSOX3054 front panel I can read:1 Mohm 15pFP6139A probe:10 Mohm 8pFcompensation range: 8pF to 18pFSo is it ok? (no matter about the 10 Mohm input impedance?)

author: TheSteve
author_rank: Unknown
timestamp: September 16, 2016, 05:04:49 pm
content: Quote from: dav on September 16, 2016, 05:00:26 pmYes, it will compensate just fine.

author: dav
author_rank: Regular Contributor
timestamp: September 16, 2016, 05:08:49 pm
content: Quote from: TheSteve on September 16, 2016, 05:04:49 pm

author: rf-loop
author_rank: Super Contributor
timestamp: September 17, 2016, 09:07:55 am
content: Quote from: dav on September 16, 2016, 05:00:26 pmScope input BNC 1Mohm15pF(+something)Probe (low frequency) compensation range8pF - 18pF. (this is for scope input capacitance)This probetipparameters 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.

author: tggzzz
author_rank: Super Contributor
timestamp: September 17, 2016, 09:59:52 am
content: Quote from: rf-loop on September 17, 2016, 09:07:55 amVery 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 seehttps://entertaininghacks.wordpress.com/2015/04/23/scope-probe-accessory-improves-signal-fidelity/EDIT: updated results at higher frequencies athttps://entertaininghacks.wordpress.com/2016/09/17/scope-probe-accessory-higher-frequency-results/

author: JPortici
author_rank: Super Contributor
timestamp: September 17, 2016, 05:29:33 pm
content: love me dat blue phosphor

author: tggzzz
author_rank: Super Contributor
timestamp: September 17, 2016, 06:01:09 pm
content: Quote from: JPortici on September 17, 2016, 05:29:33 pmTek 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-/28217155556220 hours left

author: JPortici
author_rank: Super Contributor
timestamp: September 17, 2016, 06:13:49 pm
content: too bad my money is constantly feeding my 7k addiction!

author: David Hess
author_rank: Super Contributor
timestamp: September 17, 2016, 09:08:36 pm
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: September 17, 2016, 09:32:35 pm
content: 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.

author: KE5FX
author_rank: Super Contributor
timestamp: September 18, 2016, 06:19:32 am
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: September 18, 2016, 07:32:16 am
content: Quote from: KE5FX on September 18, 2016, 06:19:32 amInteresting!Have you considered adding that tohttp://w140.com/tekwiki/wiki/p6139?

author: KE5FX
author_rank: Super Contributor
timestamp: September 18, 2016, 07:56:50 am
content: Quote from: tggzzz on September 18, 2016, 07:32:16 amAgreed, 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.

author: JPortici
author_rank: Super Contributor
timestamp: September 19, 2016, 05:03:02 pm
content: 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 a7A227A26 (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

author: tggzzz
author_rank: Super Contributor
timestamp: September 19, 2016, 05:11:30 pm
content: Quote from: KE5FX on September 18, 2016, 07:56:50 amIt 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.

author: David Hess
author_rank: Super Contributor
timestamp: September 19, 2016, 05:31:50 pm
content: Quote from: JPortici on September 19, 2016, 05:03:02 pmThe 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.QuoteThe 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.

author: JPortici
author_rank: Super Contributor
timestamp: September 19, 2016, 07:40:12 pm
content: 7A26, sorry! i tested with a 7A26

author: MarkL
author_rank: Unknown
timestamp: September 20, 2016, 02:33:25 pm
content: 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).

author: JPortici
author_rank: Super Contributor
timestamp: September 20, 2016, 06:30:56 pm
content: These probes are sold for 45. Grab somei will if there are more(The seller contacted me before to ask how they were going. I'm not sure how to interpret that :)

author: dbator
author_rank: Contributor
timestamp: September 19, 2024, 04:45:31 pm
content: Hello,Quote from: KE5FX on September 18, 2016, 06:19:32 amIs that a confirmed information? Does that happen often? Is it possible to estimate the probability? Or maybe only counterfeit probes (if there are any on the market) are affected? I wouldn't want to spend about 100 USD for one probe and then throw it out. And I need 4 pcs.I'm asking because I am about to purchase probes for my scope for which P6139A probes from Tektronix are recommended (capacitance of inputs on my scope is 13 pF). They are obsolete, but still available (second hand). I found some for sale on ebay, but from China which makes me suspicious.I would purchase new probes from Testec, TT-HF-612 or TT-HF-612RA (with readout attenuator) instead, if they did not cost as twice as the P6139A.Of course P6139B probes from Tektronix are available as new, but much more expensive than Testec probes, so too expensive for me.

author: MarkL
author_rank: Unknown
timestamp: September 19, 2024, 09:12:45 pm
content: I have thirteen P6139A probes, nine of them purchased used. In purchasing the used ones, I encountered two that had internal shorts, possibly from the whisker issue that KE5FX mentions. The resistance on both indicated the short was at the probe end, so it could have also been the tip cartridge and not the cable; I don't know. They were returned to the seller for a refund without further investigation.At any rate, that was 5 years ago, and the nine I kept are still working fine. The other four I bought new 25 years ago, and they are fine too.So... I think the P6139A is ok to buy as long as you have a return option. I would also try to get ones with as many accessories as possible (ground clip, sprung hook, color rings, etc. - see the manual) as genuine accessories can get expensive to buy individually.

author: dbator
author_rank: Contributor
timestamp: November 01, 2024, 09:37:23 am
content: It looks not definitely.I decided to not risk in purchase of those old probes.

author: BillyO
author_rank: Super Contributor
timestamp: November 02, 2024, 12:01:30 am
content: I got 4 P6139A probes a couple of years ago from various places (2 from ebay) and they have been fine. I don't think that whisker business is the pandemic it's being made out to be. On top of that you can often find ones being sold as "parts only" for a lot less where you can get replacement cables. There were a lot of these probes made.https://www.ebay.ca/itm/267039489899

author: dbator
author_rank: Contributor
timestamp: March 20, 2025, 08:39:34 pm
content: Hello,those probes were incomplete, that's why they are/were so cheap. I asked the seller couple of questions, but they did not reply.Since I can't wait anymore and I don't want risk, if I will not find soon cheaper P6139A probes I will decide for the Testec probes.edit:I decided to purchase Testec probes. It's TT-HF 612 model with banwidth of 500 MHz. I was considering TT-HF 612 RA model, but in case using them on scope without automatic attenuation detection the signal pin would scratch plastic enclosure of scope. And they already are too expensive as for private user so any money safe was playing a significant role.I decided to purchase them from a German store reichelt elektronik GmbHhttps://www.reichelt.com/which is active in some other European countries. Their customer service help line workers even speak different languages than German or English. For example Dutch or Polish.The important thing is, they have the best price and with 500 EUR purchase you will get 5% off, at another 500 EUR 10% off and at 1500 EUR 15%. Did not check higher amounts.After first of the probes arrived (they sent what they had on stock and remaining probes later, with no additional shipping costs), a P6139A which I was using in my workplace got mechanically broken (rubber part, where one usually holds the probe). That risk of using of old probes which can easily break or fail after so many years as we talked about it and lack of additional accessories and replacement parts convinced me to not purchase old used Tektronix probes. TT-HF 612/612RA have great parameters, incl. probe capacity close to capacity of P6139A.I read somewhere, the accessories are not interchangeable between probes of other manufacturers because they are smaller, but I can live with that. I don't know how long they will last, but in my opinion it's a good and long term investment.I attached couple of pictures. I hope, above information will be useful for someone of you.

author: BillyO
author_rank: Super Contributor
timestamp: June 12, 2025, 05:16:26 pm
content: It looks like many of the accessories for them would interchange with the P6139 (spring ground, BNC & SMA adapters), maybe even the clip tip and ground lead.Can you measure the diameter of the ground sleeve?

author: dbator
author_rank: Contributor
timestamp: June 12, 2025, 05:35:10 pm
content: Hard to admit, but I don't own a caliper. I tried to find one of good quality and for a fair price several times. Always when I needed to measure diameter, I borrowed a caliper.The answer is: of course yes, but you will have to wait. Unless I'll somehow measure its circumference and calculate the diameter.edit:circumference is about 0.9 mm (2.286 inch) , so d = 3.14159/0.9 mm = about 3.5 mm (8.9 inch). Since I was weak in math in school, I will confirm that by measuring the diameter with a caliper.

author: BillyO
author_rank: Super Contributor
timestamp: June 12, 2025, 05:36:43 pm
content: Thanks!

author: BillyO
author_rank: Super Contributor
timestamp: June 12, 2025, 07:07:02 pm
content: Quote from: dbator on June 12, 2025, 05:35:10 pmI can see what you mean by being weak at math.The series of number you wrote make no sense, unless you meant 9mm (.354") , then the diameter would be 9/3.13149 = ~2.9mm which seems a little small.My Tek P6139A's measure 3.45mm, which is close to what you got, but for the life of me, I don.t know how you got it.22.286mm = .9", but not the other way around.

author: dbator
author_rank: Contributor
timestamp: June 12, 2025, 07:34:01 pm
content: Few minutes ago while taking shower I noticed it's not 0.9 mm, but 0.9 cm (2.54 x 0.9 = 2.286 inch). You were fasterYes, you figured it out correctly. However, I will try to measure it using a caliper.As for the short GND spring, they are always stiff. I consider making my own which will be more flexible.Do you wish me to shot more detailed picture of the set or is it enough clear what it consists?

author: BillyO
author_rank: Super Contributor
timestamp: June 12, 2025, 07:47:24 pm
content: Quote from: dbator on June 12, 2025, 07:34:01 pmHmm, that's not quite correct. You multiply inches by 2.54 to get cm and you divide cm by 2.54 to get inches. So, to get 0.9cm in inches -> 0.9/2.54 = 0.354 inches.Quote from: dbator on June 12, 2025, 07:34:01 pmN further pictures are needed, but a confirmation of the ground sleeve diameter via caliper would be good. Just seeing if these might be replacements accessories for the P6139A.

author: dbator
author_rank: Contributor
timestamp: June 12, 2025, 08:35:53 pm
content: Yes, you're right. I usually convert from inches to centimeters, that's why I probably automatically multiplied instead of dividing. Thanks for correcting me.As soon as I will know the diameter, I will let you know.edit:I measured following parts of Testec TT-HF 612 probe (I hope this time my calculations from millimeters to inches are correct):GND sleeve diameter (for GND spring) = 2.55 mm (0.100 inches)Tip length (contact part only) = 4.65 mm (0.183 inches)Tip diameter (contact part only) = 0.75 mm (0.029 inches)Tip external thread diameter = 2 mm (0.078 inches)I had problem getting GND cable of the probe and I didn't want to damage the probe, so I didn't measure it.Comparing to Tektronix P6139A:GND sleeve diameter (for GND spring) = 3.5 mm (0.137 inches)Tip length (contact part only) = 3.4 mm (0.133 inches)Tip diameter (contact part only) = 0.7 mm (0.027 inches)GND sleeve diameter (for GND cable) = 4.4 mm (0.173 inches)GND sleeve (for GND spring) of Tektronix TPP0100 probe is 3.7 mm (0.145 inches)So that's probably why Testec call these HF probes 2.5 mm.They offer also 5 mm probes for lower bandwidth, incl. HV (non-differential), HV differential probes and other:https://testec.de/en/

author: dbator
author_rank: Contributor
timestamp: June 23, 2025, 05:51:37 pm
content: My mains power outlet is not grounded. I assumed that may be causing the 50 Hz interference.All probes were with hook probes attached. Without them attached, noise is barely noticeable. And of course after connecting the probes to 2.5 Volts square wave output on the scope (for probe compensation) or to analyzed circuit interference disappears. It is probably terminated then.By connecting banana side connector (desired for grounding strap) directly to pipe of the room heater I confirmed that - interference disappeared. Unfortunately owner of the apartment will not modify the electrical installation because it is an advanced modification of electrical installation taking much time and work and some money of course. Probably I also should temporarily move to a temporary apartment for that period of time.I know that using of not grounded mains is not safe, but I have currently no other option. At least scope is now grounded.