LM317 vs MOSFET/BJT resulted PSU for tube poweramp

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LM317 vs MOSFET/BJT regulated PSU for tube poweramp

I'm woring on the design of a PSU for my soon to be tube poweramp. Push-Pull with 4 KT88's. Class AB1. The two KT88's per side will draw an absolute max of around 800mA combined, while the other side is at cut-off and current is low to non existent. The phase splitter uses a max of 20mA at any time. Because of the given values, my design goal is a PSU for 400V@1A. I've succesully build a very nice preamp PSU with a LM317 in a high voltage configuration. For poweramp use, I'm also drawn to the simplicity of a MOSFET/BJT zener/cap follower. So I;m in doubt which route to follow.

For some reason, I can't find any schematic or text on a high voltage, high current (1A) LM317 design, while it can put out 1,5A according to the data sheet. High current MOSFETs or BJT are readily available, so no problem there.

Two questions:
- I'm I correct to assume the given current output design goal (1A)
- Is there any reason the zener/cap follower is preferred over a IC regulator
 
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You need to look at power dissipation across the regulator chip.
What is your minimum B+ for the condition when mains is at lowest supply tolerance?
The regulator must not enter the drop out region of operation after taking account of Vin ripple.

Now what is the new Vin when mains is at maximum tolerance?
What would be the regulator dissipation at this highest Vin?
 
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