[Amps] Ug2 stabilization in TMN linear amp

[Peter van Daalen]

I, being a rookie in linear amp building, am building the W5TMN TMN HF
4CX1500B linear amp ( grounded screen ).

Neither in TMN's power supply design nor  within the amp circuit itself can
I detect any stabilization of Ug2.
( The Ug2 power supply design has a choke input for filtering ( LC input, 6
Hy, 90 Ohm or less, I have 60 Ohm, 800 mA, bit overkill, yes I know ) )..

Why did TMN not design a usual screen stabilization ?
Not necessary because the screen is grounded ?
But if so, what then as to the stabilization of the floating negative
cathode potential ?

Is it safe ( with respect to Ug2 ) to build the amp exactly as designed by
John Ehler ?

I appreciate any help.
I am heavily interested in the Ug2/Ug1 stabilization theory.

Peter, PE1E.