The parts for a more powerful heater power supply arrived today, and I am pleased and relieved that the Tung-Sol/Chatham 5998 lights up and plays. As Mordy and others have noted, these power tubes sound surprisingly good as drivers. However, I notice that the LD 1+ runs pretty hot after a hour or more, so will likely put it away for now until I get an OTL amp. After all, with the Sylvania 7963 and the Siemen's C3g's on hand, it's not as if I don't have any new and interesting tubes to listen to. :)
Which reminds me...
As the Sylvania sub-miniature 7963 is considered by some to be the best double triode Sylvania ever made, I decided to compare it to a 1945 Sylvania 6SN7W. In many rankings, the 6SN7W is considered to be one of the top 4 or 5 6SN7's ever made, and it is my reference 6SN7.
I A/B'ed a couple tracks, Diana Krall, 'Devil May Care' on the 'Live in Paris' album, and Alex McMurray, 'One Step Away from the Hole' on the 'I Will Never Be Alone in This Land' album. And I was pleasantly surprised. My impression is that the 7963 sounds very similar to the 6SN7W, and maybe not all that surprising, it seems to be a tad bit quieter. The bass is detailed and propulsive, the highs are very extended and airy, and vocals have what I consider to be the Sylvania "house sound," slightly warm, liquid, smooth and sweet. Moreover, I believe the added quietness enhances transparency, imaging and sense of stage. Of course, I might change my mind over time, but for now, I consider the 7963 to be as good as any tube I have (600 and counting lol).