Another driver tube experiment to report on, and a weird one at that: a Chatham 2399. This oddball tube doesn't appear to be that common in the literature, but from what I read, it's basically a re-badged Tung-Sol 5998. I've seen a few people question whether this is the case, or that the 2399 might be sort of "in between" a 6080 and 5998. From the 5998-type dotted plates to the noticeably lower output impedance the tube yields in the cathode follower arrangement (32 ohm phones that sounded like crap on the stock circuit sound much better and balanced with the 2399), it is obviously more like a 5998 than a 6080. In fact, I have no reason to believe it is not just a 5998 in different clothing.
I have found that the 2399 is a bit brighter (or more clinical?) than the 6N13S I was using before, so the driver tube was changed to temper the overall sound. The 12BH7 sounded much worse (sharp and dry, almost sold-state sounding) with the 2399 than a 5963/12AU7, so I went back to the former. Tube rolling seems to be all about balance - a dry sounding, bright power tube may have great synergy with a softer driver tube, and vice versa. Granted, I think this also has to do with the impedance that my 300 ohm HD-650's "like to see" - lower isn't necessarily better. In this case, I seem to like the 2399/5963 combo a bit better than the 6N13S/12BH7 one used before, so I'm going to stick with that setup for a while.
