Hi The oscillator is a “works or it doesn’t” sort of thing. Frequency and output level usually are close enough to do what is needed.
Bob > On Feb 25, 2022, at 3:10 AM, Julien Goodwin <[email protected]> > wrote: > > This afternoon I swapped the fixed resistor that should have been a trimpot > back to a trimpot, and quickly dialed it up to where I was getting ~115c on > the lamp surface as expected. > > As I was in there anyway I also swapped the 20 ohm resistor back to the > Vishay wirewound part it should have been from the hack I'd made up using > cheap carbon resistors from the local shop. > > No obvious light, but I also still need to see if the excitation oscillator > is even vaguely in the ballpark (or possibly working, I may potentially have > messed with things while I was in there today), for which I'm still waiting > on some safer probe options. > > On 15/2/22 6:10 pm, Darren Freeman wrote: >> On Sat, 2022-02-05 at 20:48 +1100, Julien Goodwin wrote: >>> I /think/ it's using more power than it did before (right around 20W >>> at >>> total cold, dipping to 10W after a while), although silly me didn't >>> make >>> a note of it, but even after 30 minutes it's not locking. >> I don't have any experience with this brand/model, but I have >> resurrected some "dead" rubidium standards. I'm mostly going from >> experience with gas lasers, but I found the same approach worked on the >> rubidium units that I have here. >> It's well worth being patient with the lamp, if it's been off for many >> years, it may have a gas pressure/mix that's far from optimal. If you >> let it sit with the heater and exciter running, it may just strike >> after a while. > > I need to replace the main filter cap in the FRT power supply before I'll be > comfortable leaving it on for an extended duration, but once I do (and the > replacement is now here, I just need to hook it up) I'll be fine leaving it > on for a week or so to see. > > If it doesn't light after that, I may try just swapping in the lamp from my > house standard FRK-LN to see if it's that simple, and this has a bad lamp (at > which point I think I'd give up for now). > >> (You should measure the current going into the exciter, it should jump >> up suddenly when the lamp strikes. Measure the unlit condition with the >> lamp cold and the exciter on. On mine, the current roughly doubles when >> it is lit.) >> If it does strike, keep it running for a few days, don't power it off. >> It can get even harder to light, before it gets easier again. You might >> consider using a UPS for this procedure, as Murphy could strike just >> after the lamp does! > > Fortunately Sydney power is good enough that my UPS' have caused more outages > than they've helped with. > >> On one of my units, I had to manually run the lamp heater to a higher >> than normal temperature, before it would light. (With a thermocouple, >> it's best to use some heatsink grease, otherwise the readings can be a >> long way off.) >> The needed temperature gradually came down, until the unit could be >> reassembled and used normally. On another, I just waited for several >> hours at the usual temperature, and that was enough. Although again, it >> took a couple of days of operation before it would light without >> hesitation. >> On yet another unit, the lamp would light normally, but the photodiode >> signal was too weak to achieve a lock. (The firmware said nope.) So I >> just left it running overnight, and then after a power cycle, it locked >> immediately! >> So I wanted to point out that if the lamp has everything it needs, and >> still won't light, you might just need to leave it powered for a while. >> And you have not much to lose, if you need to run it at a higher >> temperature for a while. >> Have fun, >> Darren >> _______________________________________________ >> time-nuts mailing list -- [email protected] -- To unsubscribe send an >> email to [email protected] >> To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
