Stanford Research SR625

[taydin]

I have a chance to buy a Stanford Research SR625 for less than $2500 (I was promised a very good discount off of this price, don't know how much).

https://www.sahibinden.com/ilan/ikinci-el-ve-sifir-alisveris-teknik-elektronik-test-olcum-cihazi-stanford-research-systems-model-sr625-689874637/detay

This is a frequency counter with a rubidium frequency reference that has a 0.002 ppm uncertainty. I mainly am interested in this unit as an ultra stable reference frequency, not so much the frequency counter. But it wouldn't hurt to have a unit that can count events. The unit seems to have seen some abuse, based on the dings that are visible in the chassis. But I will be able to go to the seller and test it (apply a signal, and play with it)

What do you guys think? Is this a good deal?

[citizenrich]

Hi, I'm very new to this stuff and not experienced enough to help recommend anything. But, here are a few things that I would consider important to know that I'd expect have already crossed your mind.

If my use case or project requires a decent Rb reference, then I'd want to know how long it has been running and if it is still within spec on temperature when it is running, among other metrics. This would matter if it was bought on eBay or anywhere. If the Rb is the SRS PRS10, then that information is available (sort of) using the serial interface to the PRS10. Lady Heather can grab that information from a properly configured PRS10. But, the Rb chassis on the SR625 doesn't have an RS232 connection. The main 620 mothership does, but not the Rb side car. So, I would wonder if that info can be found out from the Rb inside. What I'm suggesting is that if you have physical access, and if it's possible, I would connect Lady Heather to do her best on it. But it may not be possible. Someone who has an SR625 must surely know. Perhaps asking the time-nuts mailing list would be helpful.

If my use case is to count things, I don't know that I would only consider an SR620 or 625. A TAPR TICC ($200) is a timetamping counter that can use a GPSDO clock (or whatever 10MHz) as the reference, and compare - or just timestamp - two inputs. The inputs need to be under 100Hz or something but that's what a TADD-2 Mini is for ($40). I suppose it matters what you want to count, if you're comfortable with dead time, the frequency, accuracy and precision. Maybe those things would help people provide recommendations.

Hope that helps and again, apologies if this is just wrong or terribly obvious.
Richard

[coppercone2]

when I was trying to build/develop best in class circuits (within reason to available resources), I was told to reverse engineer SRS stuff to see how it worked, at least for things HP does not make

[syau]

I would rather buy a GPSDO or a GPS disciplined RB reference as it will ensure that you will have a stable reference unless the SR625 is recently calibrated.

I own a SR620 and it is a must earlier to use and better compare to 52131A  (may be i am to lazy to read the manual and rather flip those push buttons and knobs  )