had my amplifer a few days and its fantastic even out the box not yet run it it sings

like others i will soon be tempted to try different valves now it came with 5U4G which a quick web search tells me is the same as a GZ34
Yet on another forum users of this amp tell me they have tried GZ32 valves
one long term user says it says here that you can use GZ32 ( not yet found said post)
has anyone a list of all valves that can be used in this great amp ?
thanks in advance