Is the anode potential increasing trick while compression takes place happening on the Neumann U47 VF14 amplifier?

Bingo. Possibly so.


See schematic with 30KΩ resistor in series with power supply:
http://downloads.bbc.co.uk/rd/pubs/reports/1954-23.pdf


See also other today's posts:
https://euroelectron.blogspot.com/2019/06/we417a-5842-electron-tube-with-pull-up.html