I lost my manual for the liquid fire and can't find any information online. What tube types doe it work with? 12AU7? 6dj8?
As far as I know, 6922/6DJ8/ECC88
As always, Alex would know best though.
7308 will probably work as well since its a 6dj8 / 6922 design.
also E88CC/ECC88/CCa works.