Active Probe recommendation? - Page 1
Forum section: electronics / testgear

author: IDEngineer
author_rank: Super Contributor
timestamp: August 29, 2022, 07:20:14 pm
content: I need to find one or more decent active probe(s). Don't have to be super fast, 100-200MHz is fine, I'm primarily trying to reduce the probe capacitance.I'd prefer to find one or more good used probe(s) from one of the "big names". When I needed current probes, I went with Tek A6302's and picked up a pair of AM503B's in a dual mainframe to interface them to the scope. I'd like to do something similar for the active probe(s) but, if possible, avoid the big-footprint standalone interface.My primary scope is a Rigol DS4054 that has the BNC's with seven spring-pin connectors beneath the bayonet cylinder. I don't know if that's some sort of standard (it's certainly not TekProbe), if power for active probes can be obtained there, etc.EDIT: I'm looking for good used operational probes, not fixer-uppers.Any advice gratefully appreciated. Thanks!

author: Someone
author_rank: Super Contributor
timestamp: August 29, 2022, 10:11:59 pm
content: Quote from: IDEngineer on August 29, 2022, 07:20:14 pmNo standard, each manufacturer has their ownlock invision.Quote from: IDEngineer on August 29, 2022, 07:20:14 pmIts there, but you'll need to reverse engineer the details. Rigol sell their inter-manufacturer adaptor T2R1000 cheap enough that it might not be worth your time (or that would be the starting point of reverse engineering). Paired with the older/outdated Tek probes like P6245.

author: MarkL
author_rank: Unknown
timestamp: August 29, 2022, 11:21:05 pm
content: I'll second the recommendation for old Tek active probes. If you're looking to minimize tip capacitance, the higher the BW, the better.You didn't say whether you want single-ended or differential. The 1.5GHz P6245 is a great choice for single-ended, IMO. I have several P6245 (amognst others) that I use with a Keysight scope with the equivalent of the Rigol T2R1000 adapter. Look for versions that have "40V pk MAX" printed on the compensation box. Later versions are only 15V pk. The 1GHz P6243 is another option with the same form factor.For low pF differential, the 1GHz P6247 or 1.5GHz P6248 are good candidates.All these probes, and more from Tektronix, use the TekProbe II interface. Now that their patent on TekProbe has expired, many of the major scope manufacturers offer TekProbe adapters. I think it's a great way to preserve an investment in Tek active probes without being tied to their scopes. Another path is to use the Tek 1103 standalone power supply, which can supply two TekProbe probes and provides BNC pass-thru to your scope, but it's not as convenient as the adapters.Be sure to adhere to the voltage limits on all these probes. And make sure you buy them with a return policy (like ebay "Used"), because a lot of them are damaged from misuse. Good, working ones can be expensive, but if treated properly they'll be around for more than one generation of scope on your bench.Edit: minor typo.

author: IDEngineer
author_rank: Super Contributor
timestamp: August 30, 2022, 02:13:12 am
content: I'm aware of Rigol's T2R1000 adapter, and don't mind buying those if that's the correct solution.Thank you for the specific Tek part numbers. That's the kind of advice I was seeking. Right now I don't need diff probes (actually I have a P6247 that needs to be repaired) so single ended will do.And the P6247 reminded me... I already have a two-channel 1103 power supply! So there you go... all I need is the compatible probes, I can use the 1103 to get from them to the scope.Thanks again!

author: IDEngineer
author_rank: Super Contributor
timestamp: August 31, 2022, 06:56:39 pm
content: Looking around at used P6245's, I see that most do not come with the little accessory kit of tips and so forth. Does anyone make an aftermarket replacement for that kit? Otherwise I'm concerned they could be so proprietary that I could end up with a nice P6245 that I can't use.

author: MarkL
author_rank: Unknown
timestamp: August 31, 2022, 10:15:55 pm
content: Both the tip and the ground sockets on the P6245 accept 0.025" posts, so there's nothing proprietary that will keep you from using the probe. Almost all the accessories could be home-made if you don't want to purchase them separately (at ridiculous prices), or can't find them already with a probe (usually the better option).A pointed tip insert 131-5638-11 is what I use the most. It could easily be a single 0.025" male-male post instead. For a ground I usually use a 0.025" male-female extender with the male end bent at 90deg going to one of their 206-0364-00 SMD clips which are quite common. Because of the low tip capacitance, longer ground leads are more forgiving for signal integrity than passive probes, so I tend not use the other very short ground accessories. (Note: Not saying there's NO ringing...)The 196-3410-00 dual-lead adapter is useful, but the one Tek makes has very stiff insulation which makes it almost useless for delicate probing. Don't waste your money on it. My plan is to build some replacements using nice, flexible silicone insulated wire.I don't use the SureFoot adapters much at all, but having one or two for each pitch can be handy to prevent shorting adjacent chip pins while probing. That's probably one thing that you'd have to buy if you need them.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 01, 2022, 02:22:24 am
content: If both the active and ground connectors expect 25mil posts then you're right, one could just fabricate anything by buying 25mil posts and soldering up what you need. Heck, you could make a custom fixture that's tacked to the board and just "plug the probe" onto the board as needed.

author: MarkL
author_rank: Unknown
timestamp: September 01, 2022, 02:39:21 pm
content: I don't think the fixture on the PCB needs to be fancier than a 2x1 0.1" header with one of the pins being ground. You could use a dual-lead adapter, or the 131-5777-00 "signal-ground" adapter which would allow the probe to sit directly on the header.The "signal-ground" adapter is a piece of springy metal (probably beryllium copper), but could be constructed out of a 0.025" pin soldered to such a piece of metal. Personally, I would opt for the dual-lead approach anyway unless I needed the best signal integrity for a brief measurement. Although designed to do it, sticking the probe on a header pin makes too much of a lever and gives me anxiety.If you haven't seen it, the P6245 manual has some good diagrams of how all the accessories are used:https://download.tek.com/manual/070899505web.pdf

author: IDEngineer
author_rank: Super Contributor
timestamp: September 01, 2022, 04:32:52 pm
content: Thanks for the link. Note that it's for the later 15V version (see page 1-8).I do give Tektronix credit for an imaginative variety of probe tips. Those were the days... T&M manufacturers just "spent the money" to do things properly. You can still find that but it doesn't feel like the automatic default anymore.

author: Domitronic
author_rank: Regular Contributor
timestamp: September 01, 2022, 06:08:43 pm
content: I understand that you prefer something used from the big brands. But to be compatible with any scope brand you might use in the future i would still consider something brand independent like the PMK Tetris 1000. Uses BNC connector but adds the hassle of an external power supply.https://www.pmk.de/en/products/tetris_serieEdit: Just saw that prices of Tetris probes increased drastically. So i would also prefer a used probe of a big brand.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 01, 2022, 10:46:02 pm
content: Quote from: Domitronic on September 01, 2022, 06:08:43 pmI appreciate the link nonetheless! In my case I already have the Tek 1103 dual channel power supply so my configuration is basically that of the Tetris probes already, and compatible with any BNC equipped scope.

author: MarkL
author_rank: Unknown
timestamp: September 02, 2022, 03:26:34 pm
content: Quote from: IDEngineer on September 01, 2022, 04:32:52 pmYeah, I was never able to find any manual old enough to show the old spec. Besides being printed on the probe, you can find the 40V spec listed in the catalogs from 1998 to 2000 or so. It's way beyond the usable dynamic range of the probe anyway.QuoteSad but true. My company purchased a brand new $20k 1GHz Agilent scope a few years back, and it came with the most embarrassingly cheap, klunky probes. Perfect for work on tubes or transistor radios. There wasn't even a purchase option to upgrade to better probes, or to delete the probes. Tossed the stock probes in a drawer unused and bought decent ones.

author: David Hess
author_rank: Super Contributor
timestamp: September 02, 2022, 07:12:05 pm
content: You can make an active probe with that sort of performance and less input capacitance than any that you can easily buy, as shown below. For higher performance, I might replace the 2N3904/2N3906 complementary follower with a 30 volt current feedback amplifier configured as a voltage follower.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 02, 2022, 09:11:01 pm
content: That's a very interesting idea. I might have those parts just lying around.Looks like a Jim Williams schematic...?

author: tautech
author_rank: Super Contributor
timestamp: September 02, 2022, 09:24:21 pm
content: Quote from: IDEngineer on September 02, 2022, 09:11:01 pmIt's not.Tek Oscilloscope Probe Circuits, a booklet or PDF everyone should have:https://w140.com/tekwiki/images/6/62/062-1146-00.pdf

author: Helix70
author_rank: Unknown
timestamp: September 03, 2022, 01:29:46 am
content: Quote from: tautech on September 02, 2022, 09:24:21 pmThat circuit is not in the link you posted??

author: tautech
author_rank: Super Contributor
timestamp: September 03, 2022, 10:48:29 am
content: Quote from: Helix70 on September 03, 2022, 01:29:46 amYes I may have fucked up as I did think it was from the Tek probe book. Maybe it is a JW design after all.

author: David Hess
author_rank: Super Contributor
timestamp: September 03, 2022, 12:53:32 pm
content: Quote from: IDEngineer on September 02, 2022, 09:11:01 pmClose, it is fromTroubleshooting Analog Circuitsby Robert Pease who was the staff scientist at National Semiconductor.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 03, 2022, 04:37:33 pm
content: Oh, I definitely know Pease. His articles were incredibly educational, just like those from Williams, though IMHO Pease could wander off onto tangents about his travels and other non-technical topics a bit too often for my tastes. I keep PDF's of articles from both on my cellphone for "casual reading" when on airplanes and such.

author: jonpaul
author_rank: Super Contributor
timestamp: September 03, 2022, 05:24:37 pm
content: BonjourActive probes are easy to damage, and hard to fix.With 50 Ohm I out scope get a Zo passive probe, eg P6156https://w140.com/tekwiki/wiki/P6156See the Tektronix Circuits Concept book Oscilloscope Probe Circuits ZoMake one for free, BNC, 50 Ohm cable, 450 Ohm series R for 10xJon