My interest in talking about kikusui power supplies was to see which technology was used in a linear solid state commercial HV power supply.
This does not change my point of view that, for a hobby application and home-made power supply, the vacuum tube solution is the simplest and safest.
I'd choose a switched mode power supply myself. It's not that difficult nowadays, even for hobbyists, with the vast range of controllers and high performance MOSFETs available.
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Yes I fully agree with this
, but did you looked at the crap schematic that 001 has posted.
Do you really believe he is able to developp and to build a switch mode power supply ?
In first instance, we should try to answer to him with an answer he is able to use....
And who will developp this switch mode power supply for him ?
Have you time and money to do it ?
You will not only have to post the schematic but also to give him all the informations about how to build the ferrite transformer and inductors....
I'm asking for some schematics suggestions.
My minimum requirement are the following:
- 0-350 Vdc (higher can be better)
- 0-30 mA (my MAXIMUM needs)
- regulation: CV/CC
- low ripple
- good stability
At this date for my experiments I'm using a Tennelec TC-952 power supply (0-3000Vdc, 10mA, 2mV ripple typ.) but it has no current regulation.
I also own a Fluke 415B (0-3000Vdc, 30mA, even more precise and with lower ripple) but it also has no current regulation; BTW this one uses a valve/tube, just to satisfy people who love them! 
What I'm asking is for some good suggestions on a schematics which can satisfy my requirements: output voltage can even be higher than 350V but current limits will never be higher than 30mA.
Otherwise any hint on a not too expensive instrument (used or new) is welcome.
P.S.: as you can see, from the output voltage of my power supplies, I already have some experience working with high voltage... 
Hybrid linear power supply 0 - 450V 30 mA Max.
Schematic of isolated power stage.
Solid state control CC/CV through opto coupler
NB: pass tube: 40W power pentode LS50 / GU50 with 12.6V heating voltage + ceramic socket
https://tubes-store.com/product_info.php?products_id=183ERRATA : T2 BF421 or BF423, not BC327
Thanks for the hint:
may I ask the origin of the schematics?
Was it tested before? I ask this because is clearly incomplete.
Nothing to worry about: I can simulate it to see if it really works
Any suggestion for the pentode to be used? Regarding Valves/Tubes I'm really a noob!
P.S.: I only now note your references to LS50/GU50 and the filament voltage!!! Sorry!!!!
Origin: my project.
Not tested.
I don't need a HV power supply, I'm retired but I'm repairing a lot of vintage audio stuffs (tubes and transistors), I'm very busy and I have no time to developp such a project, nor time and money to build a prototype.
If I should make one, it would be a 0-450V at least 300 mA in two ranges.
Solid state control CC/CV is quite easy to design for who's have knowledge and experience in op amps.
It can be very stable as every solid state power supply.
Also low ripple.