Keithley 225 Current Source - Page 1
Forum section: electronics / general

author: motocoder
author_rank: Unknown
timestamp: July 11, 2015, 04:11:54 pm
content: I have decided to sell one of my Keithley 225 Current Sources.http://www.ebay.com/itm/-/171854956041?I purchased one of these very nice Keithley 225 current sources off of eBay some months ago. The unit I purchased (not this one), had been virtually destroyed by the university that previously owned it. Because the electronics portion of the restoration was going to be so challenging, I purchased a second unit (this one) to use as a known working reference while troubleshooting. I ended up restoring the first Keithley 225 that I purchased without needing to resort to using this one as a reference. So I cleaned it up, replaced some old caps, and am now selling it. The unit I am selling is 99% original parts, and is NOT the one that required extensive repairs. I've decided to keep the one I put all the repair work into, even though it's not in cosmetically good a shape, because I am quite proud of the fact that I got that one workingHere is a list of what I've done to this unit:- Replaced an old crumbling / cracked power cord.- Replaced the two main DC filter capacitors, which were still the original leaky paper ones.- Replaced a polyester film capacitor that was buzzing.- Added an AC filter cap across the secondary winding that powers the output (this is a small enhancement that lowers output ripple and improves performance above the original specs).- Cleaned all switch contacts with De-Oxit red and re-lubricated with De-Oxit gold. Switch bearings were lubricated with grease.- Calibrated, tested, and verified all functions.- Cleaned case and PCB, polished chrome on handles, replaced outside case screws, repainted top cover.This is a great current source, and is featured in several of Dave's videos. The repair thread on the other unit (not the one for sale), including links to the manual and my annotated schematic, can be found here:https://www.eevblog.com/forum/repair/keithley-225-(current-source)-repair/

author: motocoder
author_rank: Unknown
timestamp: July 17, 2015, 09:17:24 pm
content: If anyone here is interested in this, the auction on this is almost over (closing in about 18 hours).

author: motocoder
author_rank: Unknown
timestamp: July 18, 2015, 11:28:31 pm
content: Congrats to whoever bought it. I didn't quite break even due to shipping costs, but it will be nice to have the space on the bench.

author: jc
author_rank: Newbie
timestamp: July 19, 2015, 06:53:38 am
content: It is getting a good homeI thought it was going to reach $300+, just on the improvements compared to the way it was in May.

author: motocoder
author_rank: Unknown
timestamp: July 19, 2015, 07:08:21 am
content: Quote from: jc on July 19, 2015, 06:53:38 amI am glad someone on EEVBlog is getting it. I think it sold for a fair price. I paid $250 plus shipping for it, and I wasn't expecting to make a profit.Regarding the improvements, keep in mind this is the almost pristine supply that I bought as a reference when I feared the damage to that other 225 were going to get the better of me - not the one that was so damaged and that required all that work to repair. This one is almost all the original components (just the filter caps, a buzzing film cap, and the cover screws got replaced). Also the knobs and such are in better condition. Another benefit of this one is that it has the fine adjustment knob with the "calibrated" switch (although you'll see that's sort of a useless feature). The replacement pot I used in the one I am keeping doesn't have that. It does have an added AC filter cap that reduces some of the mains noise coupling through to the output.I didn't want to sell the one I did all that repair on because it has my virtual ground circuit on a daughter-board, mounting of which required drilling a hole in the PCB, plus some traces lifted from me constantly desoldering and soldering stuff. I figured some random eBay buyer wouldn't appreciate cracking it open and seeing that, but I'll happily keep it and use it hereAnyway, I didn't get it in the post today because I didn't have a box. However, the FedEx guy delivered something that came in a box that I think will be a good one to ship this in. My wife will send it out first thing on Monday.