The IP17 Heathkit power supply does not meet your specifications: nominal 100mA, 125mA max instead of 200mA.
If you have bought one, I advise you not to try to modify or to improve it, except maybe replace V1 and V2 (OA2) with zener diodes.
I have never been a fan of these cold cathode regulator tubes, but it was the only thing available at the time.
http://www.sgitheach.org.uk/ip17.htmlIf you want to design and manufacture your own high voltage power supply, you must follow this procedure:
1) The biggest problem is the transformers.
Can not make a "custom" transformer for a single unit, the price would be excessive.
It is therefore necessary to use commercial transformers.
So the choice is limited and it will be necessary to use several transformers.
One option is to find out if a transformer for a tube amplifier could serve ... They usually have at least one high voltage winding and a 6.3V winding.
https://tubedepot.com/t/diy-central/transformers-and-chokes?page=1Another option is to use for high voltage an isolation transformer that has a 400V winding. (using secundary as primary, no problem, transformer is reversible)
https://www.erea.be/fr/produits/detail/efsp160The rectified high voltage (bridge rectifier) would then be 565V, which allows regulated output voltage up to 450V, which is ideal for those working on vacuum tube projects.
To be continued....