You might want to do a Google search for the basic principle of a wobulator.
I just searched for the manual for this thing, lucky me I found it (rare for Metrix stuff of any vintage...), attached below. A nice manual too (by French standards that is...) = 60 pages of goodness ! Complete with schematics, block diagram, how to operate it as well as principle of operation, and good quality scans to boot, perfectly legible !
Just skimmed the surface for a few seconds but it's already starting to make more sense !
Robert and ShakalNokturn helped a good deal too !
So now it's clear that it's a very specialized bit of kit, a test set for TV service techs, which I have therefore no business owning! Let's be honest... this thing is wasted if it stays with me, I just have zero use for it yet it takes an awful lot of space. The only good thing to do is sell it to someone who actually is into old TV stuff, and could appreciate this NIB piece of test gear....
So yeah. Manual helps for sure.
So basically the middle part of the isntrument, they call the "Wobulator". Generated the HF "carrier" + some frequency modulation on top of it hence as Robert said the term "Wobble". Teh amount of Wobble is controlled by that knob that gives your a few fixed spans up to 20MHz. So for starters I need to get that working !
Then the left part of the instrument, they say it generates "markers". There two kinds you chan choose from. A marke for sound, and another marker for video. Markers are at a fixed frequency, 1MHz and 10Mhz. Can't remember which is sound and which is video.
The "biscuits" one can shove into the big rotating switch, do not define the carrier/ HF frequency. They are there to provide the two sound and video markers. So for example I have the biscuit for Channel #7 on my particular instrument. That means that the biscuit I have will generate a marker at the carrier Frequency for channel #7 + 1MHz and another marker at carrier + 1MHz. That's why the biscuit is made of two identical looking sections, each with their own Quartz crystal.
Then, CRT/ scope section of the instrument, is supposed to display the amplitude vs frequency response of the TV set under test, so I guess it should look like a LPF Bode plot or something ? A horizontal part then a negative going slope on the right hand side ?!
Will try to find videos of a Wobulator in action to confirm...
That also means I need an old TV set to to wire to this Wobulator if I want it to display what it's supposed to display, pfff... how practical. Need to find a way to get round that...
Anyway, armed with this manual hopefully I should be able to fix it... or at the least have a fait go at it.
Decision is also made to sell this puppy so it can go to someone who deserves it more than I do. Hopefully I will make some profit in the process and that will allow me to buy a similar vintage Metrix boat anchor (love the look of them), but this time a general purpose RF generator with general purpose modulation features, that I can actually make use of and enjoy...