[GONE]       FS: (USA/Worldwide) 2x Keithley 236 SMU's - Page 1
Forum section: electronics / general

author: ZGoode
author_rank: Frequent Contributor
timestamp: April 07, 2025, 05:29:25 am
content: Doing a little decluttering of my homelab and could use some space back. I have 2 Keithley 236's that need a home. I no longer have a use for 3 of these units, so I am only keeping 1. As far as I am aware, none of these have any issues, and work great. I can conduct additional testing at request if any potential buyers would like proof of certain functions. These units were last calibrated in 2011, but still meet spec according to my Keithley 7510 DMM.One unit has the rack-mount ears included, so if you have a preference on rack ears or not, let me know (I am not charging extra for these). Other than the ears, the units are identical.No accessories or cables included other than standard IEC power cables.Currently asking $500 each (or $900 for both) + shipping (anywhere UPS ships, although USA would be preferred). I am open to reasonable offers since pricing on eBay is all over the place for both working and parts units.If anyone is crazy enough to trade a 34420A for both units, I would take that too (but I doubt anyone is crazy enough to do that, lol)Local pickup is available in the Phoenix, AZ area. Zip: 85295Will be uploading a few more items in the future as I continue my decluttering

author: ZGoode
author_rank: Frequent Contributor
timestamp: April 07, 2025, 05:32:00 am
content: More pictures showing operation being measured by my DMM7510. All measurements were taken using unshielded banana cables, so there was unfortunately some noise but the units both measure within specifications even with this non-ideal method. I did not have the proper shielded triax adapters to go into my DMM at the moment.

author: voltsandjolts
author_rank: Unknown
timestamp: April 07, 2025, 08:49:23 am
content: Nice. And IIUC you can upgrade them to 237.youtu.be/DLp8jdxnypc?feature=shared

author: Hydron
author_rank: Super Contributor
timestamp: April 07, 2025, 01:38:50 pm
content: I've got a partially written up post regarding the upgrade on mine (been half-written for a few years now!) - it's quite a bit of work and not that cheap, but 1100V is very nice.I DO have some boards and metalwork designed for the HV converter bit (matching the original Keithley design) that would make it a lot easier if anyone wants to try - ping me if anyone needs these. For the output stage I've also got more of the P-channel MOSFETs than I'll ever need (hard to source), and some tips on which N-channel ones work (need to watch for oscillation with some modern "equivalents").

author: ZGoode
author_rank: Frequent Contributor
timestamp: April 07, 2025, 04:24:55 pm
content: Hi Hydron,I'd love to pick your brain on the upgrade to 237, assuming you don't already have a thread started. Back when I was using all 3 236's my plan was to upgrade all 3 to 237's, but as you said, some of those parts are tricky to source.

author: Hydron
author_rank: Super Contributor
timestamp: April 08, 2025, 04:37:45 am
content: OK so the quick summary:Resonant converter - everything is pretty readily available except the case, PCB and main transformer. I've got design files for my own replicas of the first two, and used Marco Reps's suggested turns ratio and core choice for the latter (which seems to work fine). PCB is easy and cheap to get (10 bucks from JLC or something, possibly even with slow shipping), for the sheet metal case I used sendcutsend (US only until recently, not sure where they ship to now), some 6-32 male-female standoffs and some self-clincher nuts for mounting hardware. I DIY'd the case for the first conversion I did; not the prettiest or easiest job I've ever done, was worth paying 60 bucks for the professionals to do the second one.Output board - some BJT transistors aren't very available but also aren't too critical (used with base in reverse breakdown), there are expensive silva-mica caps (I'm sure film or NP0/C0G ceramic would be fine as replacements) and the output MOSFETs are the most annoying to source.My first effort with the N-channel ones ended with oscillation at the high end of the output current range; it turned out that the gate resistor values in the service manual are incorrect (real K237 output boards use 241 ohms rather than 51, on the N channel side only) and even then you need to use the right MOSFETs, STP3NK50Z seemed to do the job OK in the end.The P channel parts are harder to source, the first unit I did I used a on-semi part that is now also obsolete, for the second I found a batch of new-old-stock MTP2P50Es (got 24pcs, so I have some spares for this now). No issues with oscillation here though.Finally there are some mechanical parts that need fabrication (MOSFET clamp bars) and some wiring that needs adding - not rocket science, just needs some effort.After the first unit I converted I found a K237 output board on ebay for a reasonable price (turned out it had one dead P-channel FET) - this made converting my second K237 a lot easier and cheaper than the first.Analogue board - newer units (than Mr Reps' at least) will be missing a few required parts for the 1100V range on the Analogue board, namely 3* 1M and 1* 300K precision resistors, a couple of teflon standoffs and a special custom reed relay in the voltage sense circuit. The first three just require money to solve, the last one is only available from one seller in Sunnyvale CA (https://products.testco-inc.com/#/app/layout/itemdetails?ItemNumber=1240-0229&item_int_id=9375). You can get away without the custom relay if you move another less critical one into it's place (and change that one instead for a more available one). I spent the money on the original parts in the end (about 50% more than is advertised now annoyingly) as I was nearby Testco for work at the time (by co-incidence I am again in Sunnyvale this week, shame I don't have more units to convert!)Hope this helps, like I said I'm happy to share the design files (also for a breakout box I've made to go on the side of the 236/7), finding the time to do a more detailed write-up is the real challenge!Edit: Given the interest I'll try again to finish the write-up fully and put in some pics etc, but it's rather busy right now so no promises sorry!

author: ZGoode
author_rank: Frequent Contributor
timestamp: April 08, 2025, 06:16:54 am
content: Hydron, thanks for the write-up! I'd love to get those files/BOMs if you are so inclined. If they are Github or something similar please share the link. While I don't need the full +-1100V of the 237, I could definitely use at least +-500V for biasing my LCR measurements.I was looking at replicating Marco's work (and now Hydron's) for my personal K236, and if people are interested in a pre-upgraded unit, I'd be willing to upgrade the two other units to also be K237's for the cost of parts in addition to the original cost of the K236s.

author: guenthert
author_rank: Frequent Contributor
timestamp: April 08, 2025, 03:56:34 pm
content: Quote from: Hydron on April 08, 2025, 04:37:45 amThat was interesting already. I think in the projects or test gear section folks are more likely to search for such than in the buysellwanted (market) section though.

author: Hydron
author_rank: Super Contributor
timestamp: April 08, 2025, 11:38:22 pm
content: Yeah I was planning to make a proper thread with pics etc in a more appropriate place.

author: Hydron
author_rank: Super Contributor
timestamp: April 09, 2025, 11:58:36 pm
content: Some more notes and a pic from the last time I posted about this:https://www.eevblog.com/forum/projects/1200-vdc-resonant-converter-and-a-few-questions/msg4025947/#msg4025947Breakout:https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg5541853/#msg5541853Edit: added gerber files for the board as attachment, added correct link to pic of PCB

author: ZGoode
author_rank: Frequent Contributor
timestamp: May 27, 2025, 04:45:20 pm
content: Quote from: ZGoode on April 07, 2025, 05:29:25 amDid I price these too high? Or are they just niche enough that it is going to take a while to find an interested party? I am open to offers if my pricing appears too high, since I would love to see someone else get good use out of them.

author: zepto
author_rank: Regular Contributor
timestamp: May 27, 2025, 11:35:06 pm
content: Quote from: ZGoode on May 27, 2025, 04:45:20 pmI don't think they are niche at all. Test equipment pricing is the wild west, but this forum is full of people that enjoy buying test equipment for bargain prices. I can only speak for myself, but I wouldn't pay $800 and I sincerely doubt you paid that much. There is a balance between how much profit you intend to make and how quickly you want to free up space. Listing them on ebay/fb marketplace/cl will get you a larger audience. You might also see if there is anyone local that would trade you something useful.They are cool devices and the cost for a modern replacement is certainly much more than $800.

author: ZGoode
author_rank: Frequent Contributor
timestamp: May 27, 2025, 11:56:53 pm
content: I mean, you're not wrong about wanting bargain basement prices, I'll admit I'm in that boat too whenever I need certain things. That's why I'm willing to take offers, I'm not firm at $800 I just started there since that was what I saw in sold on eBay when I looked a while back. After paying way too much in shipping I probably paid right around 800-900 each a few years back. That's why I chose that as my starting point, but please make me an offer for a price that you think is reasonable for these units. I'm in no rush to get rid of them, but will not consider a trade since I do not have more space to take in any more equipment unless it is something I specifically need (which there is none at the moment (at least nothing I need that isn't way more expensive (like an HP 34420a) than these are)).

author: ZGoode
author_rank: Frequent Contributor
timestamp: May 28, 2025, 04:05:08 am
content: Since the $800 I started with was too high, how about $500 each or $900 for the pair?Again, I am open to taking offers (or if someone is crazy enough to trade a 34420A for both units (which I know no one is, lol))

author: zepto
author_rank: Regular Contributor
timestamp: May 28, 2025, 05:04:37 am
content: I apologize for making the assumption on the price you paid. I don't think you will have trouble selling them for that. They really are impressive devices.

author: Hydron
author_rank: Super Contributor
timestamp: May 28, 2025, 06:27:02 pm
content: New price is very fair for known WORKING units - you can occasionally get them cheaper on eBay (both of mine were low-mid 300s + shipping) but generally "for spares or repair" only until you get well above 500 bucks.I was lucky that my units were trivial to repair (both had bad fans, one had a bad mains voltage range selector switch) but it was obviously not guaranteed to be that way when buying "spares or repair" units.

author: H.O
author_rank: Frequent Contributor
timestamp: May 29, 2025, 02:24:02 pm
content: Yeah, I'm surprised they're not sold.I'd buy one of these for $500 if it wasn't for the fact that I just jumped on an Advantest TR4163 AND that these are in the US.

author: tatel
author_rank: Frequent Contributor
timestamp: May 29, 2025, 02:32:25 pm
content: Quote from: H.O on May 29, 2025, 02:24:02 pmYep. After those western couriers screw you first on shipping price, then in customs paperwork fee, and after you pay 21% VAT over all this, fair price is gone. Only way I know about getting things from the US into EU was Ebay International Shipping, and even that has got like 80% higher since Christmas. Or perhaps sellers got greedy and are putting a mark on shipping. I don't know. But you were favoring a US sale, so I guess you are OK with that.

author: ZGoode
author_rank: Frequent Contributor
timestamp: May 29, 2025, 03:25:14 pm
content: Customs paperwork and foreign shipping headaches (especially with orange man screwing with US customs) were the main reasons I would prefer US sale. Annoyingly, its easy to bring stuff into the US, but a PITA to get them out. I'm not opposed to international sale, but it'd definitely be more of a headache for both me and whoever decided to purchase.

author: tatel
author_rank: Frequent Contributor
timestamp: May 30, 2025, 03:55:04 pm
content: Quote from: ZGoode on May 29, 2025, 03:25:14 pmI would expect getting things out of the US would have little to do with US customs. Perhaps there's something about making sure not to export to Russia, DPRK, etc?QuoteFrom buyer point of view, ebay is the cheapest/easiest way. US sellers get their money once the parcel gets into the US facility in Illinois, even if article gets lost/damaged on shipping after that, and buyer is refunded. No paperwork fess. But I guess PayPal fee, could easily make it unfeasible from seller's point of view?Anyway, if they continue raising shipping price, it will also be unfeasible from buyers point of view.Good luck

author: ZGoode
author_rank: Frequent Contributor
timestamp: June 08, 2025, 04:18:53 am
content: I'm gonna throw them up on Ebay at a slightly higher cost due to fees there to try and get a wider reach. Link here:https://www.ebay.com/itm/306341351649For anyone on EEVBLOG let's go with $550 including shipping for anywhere in the USA so that anyone who might be interested does not need to worry about calculating shipping cost.

author: ZGoode
author_rank: Frequent Contributor
timestamp: June 23, 2025, 04:00:21 pm
content: The one with the rack mount ears is gone. The normal one still remains available.

author: ZGoode
author_rank: Frequent Contributor
timestamp: June 25, 2025, 02:58:48 am
content: Last unit is on hold until payment. Will update if/when this changes

author: ZGoode
author_rank: Frequent Contributor
timestamp: June 30, 2025, 11:26:05 pm
content: And the last one is gone. Found a new home with "WattsThat." Hopefully he gets many good years of use out of this device