The Champlifier and the Tweed Royal run in Champ mode (single-ended, Tone control switched off, Cut control at maximum) sound very, very similar, as you would expect they would. The only significant difference between the two circuits is that on the Tweed Royal, the signal from the second gain stage still has to go through the in-phase side of the cathodyne PI to get to the 6V6 output tube. But that's basically just a unity gain path and shouldn't alter the tonal character significantly.

I changed the tubes because I had told Keith at BYOC that I had all the necessary types and didn't need the 5-tube package with the kit. But when it arrived, they had been included anyway. So I used them for the initial start-up (I always build and test any of Keith's new kits totally stock, the way any BYOC customer would receive them) but pulled them out and am sending them back to him. The stock tubes sounded great--I'd have to do a true A/B test to be able to say which sounded better. I've got several NOS 6V6s that I'd like to try a pair of in the Tweed Royal, but they really need to be tested to determine the best matched pair, since I obtained them all as singles.