720a KVD acquired! - Page 1
Forum section: electronics / general

author: RoadDog
author_rank: Regular Contributor
timestamp: October 05, 2024, 05:33:41 pm
content: Has taken quite a while to find a 720. Most of the time when they pop up on EBay or somewhere else no one can confirm anything about them and they want a pile of money for them.Thanks to TiN I now have one. The 335a still needs some work. I’m sure it probably needs some caps replaced as it’s such a common issue with them. I’ll be on the lookout for a 721 and 750 in the next several months and stuff all this in a rack. Once I have those, sort the 335 out and get a couple of resistance standards built that I’m working on I should be able to troubleshoot and depending on the issues repair 720’s for folks.

author: The Soulman
author_rank: Super Contributor
timestamp: October 05, 2024, 07:35:13 pm
content: Congrats!Even this old "obsolete" electronics are now hard to come by. (and/or stupidly expensive!)

author: TheDefpom
author_rank: Frequent Contributor
timestamp: October 05, 2024, 08:24:30 pm
content: I recently picked up a 750 and 721, in readiness to getting a 720, I was hoping to get one from TiN as he mentioned he could get me one, but looks like you beat me to it !

author: RoadDog
author_rank: Regular Contributor
timestamp: October 05, 2024, 08:48:26 pm
content: Sorry bud! I’ve wanted one for a long time and he and I have talked a lot. He checked it out and sold it to me a while back wanting money for other projects he’s working on.I am currently setting up so I can troubleshoot and repair them. I used to work on them so I know my way around them a bit. Best of luck in your search. I would see them pop up affordably every once in a while and as mentioned most folks didn’t have the ability to perform a self cal or sometimes even verify some basic measurements.I should be able to acquire some full units and some parts over time. If/when I end up with a good unit I’ll post here about them.

author: RoadDog
author_rank: Regular Contributor
timestamp: October 14, 2024, 07:21:15 pm
content: The stack has grown. Made a low offer on the 721 lead compensator on EBay and surprisingly they accepted it without any negotiations. I’m unsure if it’s condition but should know more soon.From what I’ve read in the 335a manual I’ll need a 750 divider as well to do some adjustments to it. I’ll tear into the 335 soon, see what I find and post here when I do. Hopefully it’s easy and affordable to fix as it’s a bit drifty at the moment.

author: guenthert
author_rank: Frequent Contributor
timestamp: October 15, 2024, 07:35:10 am
content: Quote from: RoadDog on October 14, 2024, 07:21:15 pmManuals often list gear to perform performance evaluation or calibration. Those are however just hints (and usually the vendor will list its own products). Once the procedure is understood, you can substitute with other gear (perhaps some recalculation is needed). The 750A divider doesn't offer anything the 720A doesn't provide (well, it allows to adjust the input a few ppm, in case it isn't quite on spot, but you can add a pot in series with the 720A yourself and you might not want to expose the 720A to 1000V for long).Have a look at the 750A's schematic and then decide whether you truly need it or can rather replicate it yourself (you don't need long term stability).