Wow, a real education in noise sources. Tube seems fine after lots of misc. tests and changes. The mic and cable is fully assembled, but the sh%tpile of temporary PSU and transformer connections is held together with clipleads. Once additional filtering was put on the separate filament and B+ PSU's and the output transformer was added it got reasonably quiet. There's still an audible hiss level not present in the SS version, and I'm betting some amount is traceable to the sh%tpile. Will put a proper PSU together next before trying other tubes. I had a 50K wirewound pot for adjustable Rk initially, and metal film Rk was a noticable improvement in noise.
For the record, so far with the 5977 I'm showing 95 VDC B+ @ 4.5 mA with a 10K Rk, all that yielding 45 VDC at cathode for bias. Rk sounds low to me, and current high. I was thinking a low mu triode was a better cathode follower choice than med. or high, but I took that from memory without checking. Time to be checking my options again.