[Dekatron]

This document: http://electrojumble.org.uk/Mullard_PotCore_Equivs.pdf says that the LA2401 core is obsolete and should be substituted with LA1224 cores. Some data on LA1224 can be found here: https://www.tvsat.com.pl/pdf/K/kat_mullard.pdf which says:

LA1224 Pot core 21mm A13 (3h1) µe = 100 with adjuster at mid range position, Adjuster LA1502