I absolutely love this little amp. It seems like it gets mentioned time and again tangentially in other threads. I think it deserves some time and space to itself. There are a few variants out there, so go ahead and note what you've got - you may teach us something in the process. Mine is a B-15N with 3x6SL7, 2x6L6GC, and a 5AR4 rectifier. The cab is coverd in Tolex, and there's no plexi logo or anything. The driver is a square magnet, OEM-looking thing. I'm thinking CTS, but I'm really no historian with these. Driven just a little bit hard, the response is really amazing. The punch is just right for the sound I hear in my head, but when you get a drummer a bit excited, it runs out of gas. Using 350B tubes in place of the 6L6GC helped a bit, but they are very expensive. Using red-base RCA 5691 miltary version(I think-and I'm too lazy to check-sorry) in place of the cheesy EH 6SL7 made a noticable and more affordable improvement. I can't think of a better amp for recording as-is. Changes made upstream are reproduced well enough, and even the POS stock speaker mics up well with a large-diaphragm condenser of reasonable quality. So. anyway, tell me about your beloved B-15 (or B-18, for that matter). Any mods done to it? I've heard about low-pass filters in the circuit to help with output, anyone remove these? OK, dinosaurs, let's hear about those old crusty B-15!