WTB: Tek A6302, AM503B, and TM501 (current probe setup)

[IDEngineer]

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!

[andy3055]

Not sure if this will help:
https://surplus.ucsd.edu/Listing/Details/1833718/PROBE-CURRENT-INDUCTIVE

For 25 bucks, it is a steal!

[IDEngineer]

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!

[andy3055]

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.

[IDEngineer]

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!

[andy3055]

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.

[IDEngineer]

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....

[andy3055]

Try it on Friday and keep me informed if I can help. Good luck.

[IDEngineer]

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.

[andy3055]

That is good news!

[PartialDischarge]

Don’t buy an Am503B unless you can calibrate it, it requires a special tool. Thats why I prefer the older AM503

[IDEngineer]

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?

[PartialDischarge]

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.

[IDEngineer]

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.

[IDEngineer]

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.

[PartialDischarge]

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

[IDEngineer]

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!

[IDEngineer]

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.

[andy3055]

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!

You 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.

[IDEngineer]

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?

[IDEngineer]

Now, the hidden detail is that the AM503B requires a GPIB card to adjust it like the AM503.

Hmmm... 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.

[PartialDischarge]

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.

[IDEngineer]

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).

[IDEngineer]

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.

[andy3055]

Looks like you are very lucky these days. Did you consider buying some lottery tickets?