I can't get an accurate mental picture of how you have it connected up. Can you post a schematic?

How much voltage creep do you see?

What precisely do you need 200 V DC for? Plate current for a tube circuit, I hope?

You generally can't find 200 V zener diodes. None that I remember seeing. Higher current lower voltage perhaps?

I'm unregulated
Mx. Remy Ann David

Remy yes you can easily get 200V zeners as I have bag in my hand right now. Yes its for tubes...

Boswell I will PM you the Schematic, its in its first stages....
The creep is 50mV every 2 seconds or so. But it keep rising. The 5K resistor might be need to bigger as the 5W resistor may be getting a tad warm.

Ok so its really cold in my garage I guess. The voltage stabilized at 204.1VDC after 30mins with the pot removed. So I will try with the pot in again tonight. I must just been to impatient. Every pot change takes 30min to stabilize, that sucks. How would I apply negative feedback to the base of BJT? Through a blocking diode in series with a resistor (output to base)>? Would I need a blocking diode from the zener to the base as well?

I don't think there is anything wrong with any piece of equipment that requires 30 minutes or even more to get up to its proper warmed up operating parameters. Just because we have gotten used to instant on with our silicon-based solid state equipment doesn't mean it's " instant warm-up". So you're going to have to wait for circuit boards along with their associated chassis components come up to temperature for any kind of expectation of proper operation. In fact, it actually used to take brand-new Ampex MM 1200 & MCI JH 100/114/24's, 3M M-79's, took 3 FULL HOURS before you could expect stable operational alignments. So don't be impatient, it ain't drive-through McDonald's. Combine that with a broader range of operating environments i.e. colder than 72°F or warmer than 72°F will also cause operational variations over different periods of time. Just because you want something to be just so doesn't mean it's going to cooperate in a positive manner. If it did, it either wouldn't be made in China and/or it would be a perfect world.

It's tough to find quality made components in Japan anymore especially when all of their stuff is coming from China. China should just stick to take-out joints & home deliveries.
Mx. Remy Ann David