I know that many have tried a 12BH7 in place of the 12AU7 for the concertina phase inverter. I read somewhere that nine out of ten people will say the 'BH7 is the "better" tube. I also read somewhere that the 'AU7 has lousy specs - never intended for audio use, horrible distortion specs, blah blah blah. Anyhoo, many will say they like the ‘BH7 better, and a few will say they like the ‘AU7, but no one seems to say
why.
I'm trying to understand what makes a particular tube a "good" choice for the cathodyne splitter. I found a relatively simple to understand description here:
http://www.freewebs.com/valvewizard/cathodyne.html
I've managed to grasp about the first four paragraphs. I'm still working on the rest. In the meantime, I've spent a lot of time swapping my JJ ECC82 with an Ei Yugo 12BH7. In general, I try to be the skeptic. I want to believe that all tubes sound the same. I've got tin ears, and all the golden ears have had a glass of wine (or three) too many. Despite my stubborn and generally pessimistic attitude, I'm afraid I'm starting to develop some strong feelings about the way the 'AU7 and the 'BH7 sound. And yes, I think they do sound different.
I think the 'AU7 gives the appearance of having more bottom end. It sounds fuller, or deeper and richer. I don't think it actually renders the lower octaves "better" - in fact, I fear it may be the opposite. It could be that it is sloppier on the bottom end, but the slop gives the bass more body in a way that sounds full and appealing. It may be doing this at the expense of the mid and upper ranges. The effect is particularly noticeable on piano, acoustic guitar, strings, and vocals. I've been listening to a lot of Natalie Merchant, Indigo Girls, Sarah McLachlan, and Lorena McKennitt recently.
I think the 'BH7
really brings out the detail in the mids and highs, but the bottom nearly suffers. It loses some of the richness that it had with the 'AU7. I'm guessing the 'BH7 is more "accurate", and overall I prefer to have the detail. But, I can't help but miss what I'll call the warmth of the 'AU7.
Am I completely off base? Have I had a glass of wine (or three) too many? Has anyone else felt the same way as I about these two tubes?