Interestingly, Marshall supplied Shuguang (Marshall branded, same as Ruby) 12 AX7s in the preamp of my new Jubilee, and Tung Sol EL34s which I believe are Chinese origin too. I've got another gold Marshall-labelled AX7 I pulled from a Laney A100 head a few years ago that is a bright but decent sound - not classic Fendery really. I have a pair of old Mullards (I think 70's single halo) EL34s I'm going to try and tons of US and Euro 12AX7s. But the stock tubes in this work. Many Marshall 'guys' say the Chinese preamps with the metal 'E' holding the mica apart are the best in these particular amps. I am going to do some swapping, but so far I see no reason to change other than curiosity. I gotta say - it's got no shortage of poke, but the whole amp is quiet regardless of what channel is engaged. I have to look all the time to see if I have the 'Lead' channel engaged before playing. Gotta put a LED in the footswitch.