my 125B London Underground (with the Particle Accelerator tonestack/fender) just arrived:
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first impressions after spending about 10 minutes with it. it sounds very good and much better than the particle accelerator that i had. IMO, it almost has too much low end but that can be alleviated by turning the bass control down. It's capable of quite a bit of dirt but IMO it sounds best for clean and low to moderate overdrive. with the gain dimed it can get a little spongy/messy, but some might like that sort of thing.
it's definitely a keeper, but it makes me wonder what it would sound like a full sized 12AX7A.