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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