Ok so maybe it was a little too easy at first sight !
The Perfectone crystal is sadly nothing like the ACL. At first I couldn't find it. I was looking for the metal enclosure crystal like the one on the ACL or any electronic circuit i'm used of. Then I wondered about the vacuum tube I found... Could it be it ? A quick internet search confirmed that some quartz crystal can be found in vacuum tube enclosures. But the one I have is wrapped into some old foam, so I can't say for sure yet. The foam is held tight against the tube by two soldered wires, and as I'd have to remove them to access the tube, I thought it'd be wiser to ask some advice here first before doing anything stupid. Here's what it looks like :
The tube has 7 pins, I wonder if messing with those could easily alter the frequency...
On the back of this board, you can see written : "base de temps quartz 20900" (time base in english). Seems to be the frequency, but it's not specified wether it could be 20.9 kHz or mHz (seeing similar vintage crystals, I'd say the former).
Anyway I fear finding a matching crystal for 24 fps (something like 20,064 kHz) will be next to impossible with this kind of obsolete electronics. But seeing how big is the crystal tube, I doubt very much there was two of them in the 24/25 version, so there must be another way around ?
Any insight ?