WTB: Tek A6302, AM503B, and TM501 (current probe setup) - Page 1
Forum section: electronics / general

author: IDEngineer
author_rank: Super Contributor
timestamp: October 21, 2020, 05:07:03 pm
content: I had one all lined up, and then the seller sold it out from under me to someone else.If anyone knows of a setup in good condition, I'm actively shopping and ready to buy. I'd also take an A6303 (100A pistol-type probe) in addition to the smaller probe if available.Thanks!

author: andy3055
author_rank: Super Contributor
timestamp: October 21, 2020, 11:50:53 pm
content: Not sure if this will help:https://surplus.ucsd.edu/Listing/Details/1833718/PROBE-CURRENT-INDUCTIVEFor 25 bucks, it is a steal!

author: IDEngineer
author_rank: Super Contributor
timestamp: October 22, 2020, 12:11:44 am
content: You're right, it really is a steal, but 1) I'm nowhere close to UCSD, 2) I bet they don't ship, and 3) 50A with the A6303 is sufficient for my needs. I'd definitely take it if it was within reasonable driving distance, though.Thanks!

author: andy3055
author_rank: Super Contributor
timestamp: October 22, 2020, 12:18:57 am
content: Where are you located? Not in CA? You may want to call them and see. I am sure they will oblige. These being surplus, hardly anyone will show interest and I don't think a lot of people don't know/contact the store.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 22, 2020, 12:24:10 am
content: The "ID" in my username means "Idaho". It's quite a drive to San Diego from here. {grin}You have a good point. Nothing to lose by contacting them. I'll follow up and see what they say. Thanks!

author: andy3055
author_rank: Super Contributor
timestamp: October 22, 2020, 12:29:57 am
content: That is too far of course. I am in the bay area and at the moment I am in San Diego! I wonder if you could pay for it and have them release it to be picked up by me. I can ship it via FedEx then.Best is to ask if they can ship though. Make sure of the condition. You don't want to go into all the trouble if it does not work.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 22, 2020, 12:40:24 am
content: I'll bet they have no idea if it works, and no way to test it. Something tells me the folks running the surplus center aren't EE candidates.For $25 I'd take the chance. Worst case I could part it out and offer the components to folks here on EEVblog to get/keep others functional.I sent them an email per their instructions. I just got a reply, saying email is wrong and I need to fill out some kind of online form. We'll see how far this rat race goes!EDIT: Clicking on the link they gave in their email took me to a page where I can open a ticket, which is what the email says to do. I click on the "ticket" link and I'm asked to log in to their Active Directory system. Oddly enough, I cannot remember my UCSD username and password.They're open again on Friday, I'll call if I remember. If their online presence is any indication I suspect it will be a long, complicated process. Might be fun to attempt navigating a fresh new bureaucracy....

author: andy3055
author_rank: Super Contributor
timestamp: October 22, 2020, 01:00:45 am
content: Try it on Friday and keep me informed if I can help. Good luck.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 22, 2020, 03:28:16 pm
content: Remarkably, I got a personal email this morning from someone with the Surplus Center! They are going to investigate shipping options.I am extremely impressed that I got a response at all, and even more so that they are willing to entertain shipping something.I'll keep this thread updated. Hopefully it works out.

author: andy3055
author_rank: Super Contributor
timestamp: October 22, 2020, 03:49:38 pm
content: That is good news!

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 22, 2020, 08:08:05 pm
content: Don’t buy an Am503B unless you can calibrate it, it requires a special tool. Thats why I prefer the older AM503

author: IDEngineer
author_rank: Super Contributor
timestamp: October 23, 2020, 01:45:11 am
content: Really? I didn't know that. I've used AM503's but not the B version. I didn't know there was a calibration difference. What is that difference?

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 23, 2020, 08:01:42 am
content: The screws on the probe itself provide limited adjusting range, which is what you see in the adjustment procedures in the User Manual. The AM503 has internal potentiometers to adjust it further.Now, the hidden detail is that the AM503B requires a GPIB card to adjust it like the AM503. See document 070-9352-01 page 15.Do you really need it? People buy these probes/amplifiers and expect to measure reasonably well like any DMM does. My experience is the contrary. Error has been terrible when I connected various A6302 with AM503s. So I made my own setups to calibrate these probes in the range I wanted to: one setup to generate 50Hz currents in the 50-200A range with a precise 100mV/A output against which I calibrate the AM503, and another to generate 50A fast square wave pulses and calibrate the HF response and gain.Once I bought a shiny AM503B just like you from Asia, ended up selling it locally for a lower price once I realised I could't really adjust it.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 23, 2020, 03:34:26 pm
content: Good point. I noticed that reference to GPIB in the B's manual but didn't dig deep enough to realize it was involved in calibration.Jim Williams was correct: There's a lot to be said for "old-fashioned" test equipment that doesn't require a room full of dedicated tools to maintain!I'll refocus my attention toward AM503's. That's what I've used personally anyway, it will feel very familiar.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 23, 2020, 04:46:58 pm
content: Hmm... I've grabbed the AM503A service manual. Section 5 is the calibration section. It specifically says there are no adjustments on the amplifier. In fact, the only adjustments "in the system" are three on the A6303 (100A pistol style) probe, meaning there are none on the A6302 probe (and I don't remember there being any when I used to work with one daily).This implies there are no adjustments anywhere in an A6302 setup. I guess that does confirm that no GPIB calibration devices are required! {grin} But it does beg the question of how one would ever calibrate the system with the 20A probe... even if the AM503 has an internal reference, it has no way to know if the A6302 probe is reporting accurately.

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 23, 2020, 05:06:47 pm
content: The Am503A is similar to B. When I mentioned A6302 I meant to say A6303 which is the one I use and has the 3 adjustments. The 6302 does not have any tunings. So any adjustments must be made thru the AM503A gpib, and I guess some pdf service document for the Am503A is missing

author: IDEngineer
author_rank: Super Contributor
timestamp: October 24, 2020, 12:56:38 am
content: Surplus center update: The A6304 is bought, paid for, and on its way here. Shipping was $27 so $52 delivered, which I consider quite reasonable. Once I manage to find an AM503 and TM50x I will test it and report. If it works great! If not, and it's irreparable, I'll make its parts available to keep others alive.Thanks again for the tip on this probe!

author: IDEngineer
author_rank: Super Contributor
timestamp: October 24, 2020, 01:00:52 am
content: Bummer... I just read on Tek Wiki that the A6304 *only* works with the B version of the AM503. Looks like I'm destined for the GPIB version after all. Not sure it matters anyway since the pre-B versions don't offer any calibration within the amplifier.

author: andy3055
author_rank: Super Contributor
timestamp: October 24, 2020, 02:19:16 am
content: Quote from: IDEngineer on October 24, 2020, 12:56:38 amYou are very welcome. $27 shipping is not bad with a carry case! Hopefully it will get there intact as the carry case is going to protect it.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 31, 2020, 12:38:06 am
content: The A6304XL has arrived!Overall it's in very good shape cosmetically. The carrying case is pristine except for what was probably an asset number written in sharpie, which I chemically removed. The foam inside had completely disintegrated, making a huge mess of everything including the probe. However, some careful cleaning combined with an air hose restored it nicely. There isn't a single mark or imperfection on the probe, cable, or connector that I can find.The all-important core faces were in pretty good shape. I cleaned them up with some 400 grit sandpaper and they're ready to go.JUST KIDDING.I didn't touch them, not even with my fingers nor with pressurized air. They appear to be perfect, flat, and unblemished as far as I can tell without optical measuring equipment. The foam "dust" didn't get inside the jaws so the core faces and the epoxy in which they're embedded were clean.The cable was sticky from foam residue but that cleaned up easily. The gold contacts are straight and still have their gold plating.I can't actually test it until I get an AM503B (this probe unfortunately requires the "B" version). But so far I can't complain for $52 delivered.This sidearm-style probe has a mechanical lock at the back where a traditional sidearm's hammer would be located. Given the rather long distance that its jaw opens, I expected that the core faces would retract apart to protect themselves, then actuating the lock would squeeze the closed jaws together to achieve good coupling. However, it doesn't appear to work like that which suggests the cores just scrape across each other {yikes} in normal operation. Does anyone know if it was supposed to do a retract/squeeze, and perhaps this one is aged a bit? Or do they actually intend for the faces to scrape?

author: IDEngineer
author_rank: Super Contributor
timestamp: October 31, 2020, 12:58:16 am
content: Quote from: MasterTech on October 23, 2020, 08:01:42 amHmmm... further investigation reveals that it is the AM5030 that has a GPIB interface. The "AM 503B & AM 5030 Amplifier Instruction Manual", page 2-13, specifically says "This material applies only to the AM 5030 Programmable Amplifier. The AM 503B does not support a GPIB interface." And reading the testing and maintenance section finds no mention of GPIB for the AM503B. This is from Tek document 070-8766-05 dated 1994. The document you're referencing doesn't have a copyright date, but both docs specifically say they apply to "firmware version 3.0 and above" so I'm tempted to presume they are comtemporaries of each other.One doc says "The AM 503B does not support a GPIB interface." The other says "The AM 503B amplifier requires the GPIB test fixture in order to set the internal calibration constants." Maybe the first reference is meant to suggest that you cannot externally use the GPIB interface under normal operating conditions, but "does not support" is rather unambiguous. Not sure what to think, other than since the A6304XL requires the "B" version I'm sort of compelled to use that version.

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 31, 2020, 04:04:11 am
content: Well, let us know how it turns out. Easiest is to calibrate the dc level with a power supply. Measure precisely 2 or 3 amps with a DMM and place a few turns of this shorted loop in the probe core. That way you should measure precisely 10 amps for example.

author: IDEngineer
author_rank: Super Contributor
timestamp: October 31, 2020, 11:46:36 pm
content: Made an eBay offer on a dual setup with two AM503B's in a TM502 plus two A6302's. 30 day money back guarantee. It was just accepted and I've just paid. Obviously I hope everything works as promised, but I figure this way I'm upping my odds of getting at least one operational amplifier and one operational probe. I'll report once it arrives and I test everything (including the A6304XL mentioned above).

author: IDEngineer
author_rank: Super Contributor
timestamp: November 06, 2020, 06:34:28 pm
content: I promised to report back.The equipment arrived on schedule. The packaging was the best I've ever seen, a sort of generic cardboard suspension system that floated everything in free space within an outer cardboard box. Inexpensive yet brilliant design. I'm embarrassed I didn't think of it.The A503B amps both powered up with an error related to loss of factory calibration, which in turn suggested was related to a low battery. I popped out the Type 389 coil cells and both were flat dead. I grabbed a couple of new ones, popped them in, and after one more error cycle (which the manual says will happen, they're warning you that the calibration is going to factory defaults) the amps now power up just fine.The A6302 probes are in very good condition. The all-important core faces look perfect. There were various old asset-tracking labels stuck to the probe bodies (putting stickers on good T&M equipment should be a criminal offense!) which I peeled off and then removed the latent adhesive. One probe looks basically new; the other is missing its Tek and serial number labels but otherwise looks new too. Both have calibration stickers on them from 2018 so they've been treated well at least up to perhaps two years ago.The dual system functions well. I've run parallel tests on them with DC, AC, and AC+DCbias currents. The outputs mirror each other (relative) and are pretty close to my references (absolute). My references aren't lab grade nor traceable anyway, so maybe the new setup is the more accurate! You can see the response drop off as you get into the 10's of MHz, as expected. Noise floor is quite low; one side is a bit noisier but I haven't yet determined if it's the probe or the amp. Even the noisier one is definitely usable at its lowest range, so this is just typical production variation.I haven't yet tried the A6204XL 500A(!) probe gun, as I don't have anything that runs that much current on the bench at the moment.Overall I'm very pleased. The eBay seller was super communicative when I raised questions about the initial errors, and even offered to credit me back for the batteries (I declined). So there are a few good eBay sellers out there.So far a good ending to the story. I'm looking forward to having better visibility on my projects in the current domain.

author: andy3055
author_rank: Super Contributor
timestamp: November 06, 2020, 07:25:13 pm
content: Looks like you are very lucky these days. Did you consider buying some lottery tickets?

author: IDEngineer
author_rank: Super Contributor
timestamp: November 06, 2020, 07:50:15 pm
content: Thanks, but I have more faith in my odds with used T&M equipment than with a lottery ticket.

author: andy3055
author_rank: Super Contributor
timestamp: November 06, 2020, 07:52:21 pm
content: Agreed! Well, hopefully you will make good use of the newly acquired treasures.

author: MarkL
author_rank: Unknown
timestamp: November 12, 2020, 04:41:36 pm
content: Have you tried looking a a fast-edge square wave with your A6302's?A few of us have been comparing our Tek DC current probes here:https://www.eevblog.com/forum/repair/tektronix-tcp202-current-probe-repair-schematic-and-suggestions-needed/msg3124674/#msg3124674It sounds like you got a nicely working set. It would be interesting to know if you have any of the flatness problems some of us are seeing.

author: IDEngineer
author_rank: Super Contributor
timestamp: November 12, 2020, 07:47:51 pm
content: I hadn't seen that thread. Let me Rube up a test environment and see what I find. I'll report back. Thanks!

author: IDEngineer
author_rank: Super Contributor
timestamp: November 12, 2020, 09:55:25 pm
content: Here are some screenshots from a quick test I threw together. There are other things running on the bench, some of which involve several amps of PWM, and I didn't take the time to isolate well so you'll see some crosstalk in the signals.Setup: Siglent SDG2042X, channel 2, square wave at 50% duty cycle, 50 ohm output into 50 ohms, 500MHz 10:1 scope probe across 50R termination, A6302 on center conductor of BNC with no probe ground lead, A6302 jaws locked but no additional external pressure applied.I took screenshots at 1MHz, 2MHz, 5MHz, and 10MHz. You can definitely see the response tapering off at the higher frequencies but honestly, I'm not disappointed. I stopped at 10MHz because we're pretty close to a sine wave at that point.This is just one of the two A6302+AM503B pairs that I purchased. I happened to have this pair hooked up and running another test so I just moved it to take the screenshots.EDIT: Rise/fall time of the original signal is about 10nS when I zoom in with the scope. Rise/fall time of the A6302+503B signal appears as ~20-25nS.

author: MarkL
author_rank: Unknown
timestamp: November 12, 2020, 10:56:42 pm
content: Thanks for taking a detour to do some screenshots.The flatness problems seen in the other thread were at lower frequencies, like around 10kHz, where you can see the crossover between the Hall sensor and current transformer. It looks like you're starting to get some tilt at 1MHz. Would you mind posting another screenshot or two at lower frequencies (like 10kHz and 100kHz)?I think the A6302 should have a little better rise time than what you're showing in the 10MHz shot. Below is what I get on my A6302 for 10MHz (avgs = 16). Maybe your BW limit is on?EDIT: It appears we also did some tests at around 500Hz. That's where my A6302 really showed its flatness issue.

author: IDEngineer
author_rank: Super Contributor
timestamp: November 13, 2020, 04:23:31 am
content: Yep, you were correct - the bandwidth limit was enabled. As I said, I just grabbed it from another test and I didn't remember I'd turned on the filter.Here's a whole set of test frequencies, from 500 Hz to 10MHz, plus a rise time shot at the end. I connected up both A6302's and put one on the center conductor and the other on the shield to get "matching" measurements for easy comparison. I didn't do averaging so the noise you see is real time.I do see a bit of imperfection at the 10KHz range you mentioned. It cleans up at other frequencies so it may indeed be related to the Hall-to-transformer transition.I'm surprised that the 5MHz and 10MHz results aren't better given that the filters are off now. However, the rise times (taken with a 100KHz signal) are reasonable and the fall times match them.

author: IDEngineer
author_rank: Super Contributor
timestamp: November 13, 2020, 04:24:08 am
content: Here's the rise time screenshot (the board won't allow more than 10 images per post).

author: MarkL
author_rank: Unknown
timestamp: November 13, 2020, 08:03:36 pm
content: Thanks again for running and sharing the extra tests.I'm coming to the conclusion that the vast majority of these style DC probes have some aberration associated with them. At least the Tek ones, which is all I have experience with.The specification for aberrations for the A6302 is +/-7%, which is a pretty wide berth. An "aberration" means anything outside of ideal. Your A6302's are definitely on the low end of that. Mine unfortunately is not, and is on the order of +/-5%.It's too bad there isn't more tweakablity in the probe or amplifier. With more adjustable low, high, and band-pass filtering I'll bet they could be made almost perfect. Perhaps a project for another day...Quote from: IDEngineer on November 13, 2020, 04:23:31 amThe rise time for the A6302/AM503x is on the order of 7ns or less, so you really need a faster input edge to measure it more accurately. For the numbers you're showing and ignoring the scope, I get about 5.3ns and 5.7ns for the probes (66MHz and 61MHz). That's not too far off, but is still awash in error.In lieu of a faster edge, you could measure the -3dB point, if you're curious and want a more accurate number. I'm sure it's fine.

author: IDEngineer
author_rank: Super Contributor
timestamp: November 13, 2020, 10:12:24 pm
content: Yes, you're correct about needing a faster source. That AWG is all I have, unless I try some of the calibration outputs on my scopes - but they likely cannot drive much of a load so there wouldn't be much current for the A6302's to sense.I've always thought the Tek probes used a strange architecture. Anything that uses multiple techniques for different parts of its dynamic range is going to have difficulties in the transition regions. One of my bucket list items is to spend some time dreaming up a better way to build a DC-to-MHz current probe that doesn't resort to such schemes. I'm honest enough to concede I'm unlikely to come up with anything better... far smarter people than me have been working on that problem for decades.I also agree with your point about the lack of "tweakability". Particularly given the contrast with Tek's own diffprobes like the P6247, which has a daunting array of trimpots inside to permit proper calibration. Why not, then, provide the same with their current probes? Even if it means the probe has to be tied to a specific AM503x and the adjustment has to be performed in the amp instead of the probe?Oh, well. I've come to accept that current probes are like the oscillosopes you use with them: Meant to let you know what a signal generally looks like, not to precisely measure it. In that respect my A6302's are working just fine.