[time-nuts] Re: An update on my Efratom FRK with "inoperative lamp"

[Bob kb8tq]

Hi

Adding insulation to an Rb is a very tricky thing. There are 
two heated zones. They need to both be at the correct 
temperature. If the “cold one” gets to hot, things stop working. 

No, this isn’t the root cause issue here. If you bulb does not light 
then that’s the root cause. Bulbs do go bad. 

Bob

> On Mar 8, 2022, at 8:33 PM, Julien Goodwin <time-nuts at studio442.com.au> wrote:
> 
> As the project has now stalled I figured I'd send another update on my FRK with the current state.
> 
> The FRT:
> Although the replacement cap I'd picked up (KEMET PEH169MD4470QB2) was perfect in two dimensions plus the mounting, it turned out to be way to tall. I'll pick up a smaller option at some point (PEH169KB4470QB2 looks to be right), but for now I'll just avoid running it for extended durations.
> 
> The FRK lamp board:
> The excitation oscillator is absolutely working. I'm still waiting on some sensible probing to tune, but it's putting out decent power within the right band, which many of you seem to confirm should be fine.
> 
> After swapping the trimmer back in the heater is absolutely heating hot enough, and if anything too hot. I've tuned it back down to roughly right.
> 
> I don't have any great options for thermocouple probes (just the classic K-type beads) so it turns out to be easy to tune things well over if the thermocouple isn't making decent contact. Suggestions welcome (although non-contact options won't work here, see the next paragraph).
> 
> New thermal insulation has absolutely helped power usage, not a surprise. I filled the lamp cavity, and also put a thin sheet over the OCXO cavity, it may also make sense to also add a sheet behind that board, but I can always do that later.
> 
> Sadly, despite all this it still doesn't lock after being left for a few hours, and I don't see any light when I look at the lamp (with ~no ambient light). As mentioned above I'm not willing to let it burn for a week so Darren's suggestion isn't currently practical. I did heat the lamp to ~240c early on based on some discussion a long time ago on this list, but that was before I'd fixed the excitation oscillator.
> 
> For now this is stalled until I either pull the bulb out of my house standard for a test, or get a parts unit, and thanks to Max for offering one the latter may happen soonish.
> 
> Once again, I appreciate all the experience you've shared while I work on this.
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