I thought I would have a look to see what kind of tubes I already have in my 2204.
The EL34 output tubes are labelled “PM Power Tubes”. Mine were bought back in 1994 and are seemingly still available here.
The pre-amp tubes are ECC83 (apparently the British model number for 12AX7) branded as Zaerix. This thread discusses their origin a little bit.
As far as knowing which tubes to buy to replace them? Hard to tell, to be honest. From what I’ve read, the tubes I have ought to sound somewhat mediocre, but they don’t My amp sounds great. I found an interesting discussion here outlining different brands and the author’s experiences with them.
So my dilemma is this: Mr Eurotube (who really knows what he’s talking about) does not rate Groovetube EL34-M tubes at all. These are the pair I have ordered (and in fact they arrived at home today). But Mr Mitchell, the author of the book I have been using won’t use any other brand (well, perhaps Mesa Boogie tubes). What may be going on here is that this information is 20 yrs old and since then companies like J.J. (available through Eurotubes) have sprung up and produced much much higher quality tubes.
I’d love to hear Mr Mitchell’s more recent opinions on tubes. I wonder where he is these days?