hi Dave,
sorry for deviating [slightly] off topic something that rarely happens here on AOS :eyebrows
anyway, i think what we are all trying to say is, concentrate on improving on the the things that are imediate, ie; power supply caps, Diodes, coupling caps, bypass caps etc, the AC heaters in this amp should be sufficient as far hum and noise are concerned as long as they are either center tapped or have one end fixed to earth/chassis. better valves are always a choice of the end user, NOS valves [on the whole] do tend to be made better than most of the current production, however, original old stock valves like EL84 etc are becoming very scarce now so dont be surprised if you see for eg Mullard versions fetching upwards of £60-00 each!
hope this helps.
Anthony,TD...