Thanks for the responses. All tube are firmly seated in their sockets. (This is not my first tube amp, nor is it the only one I have currently).
The tube in question is a Russian Tung-Sol. Only the top glows faintly. I have purchased all new tubes for the amp, as I believe the tubes are the original ones that came with the amp. The new 6SN7 and 6BX7's are on their way from Andy Bowman at Vintage Tube Services.
The 6SN7 would be hard to tell from a new one, it looks perfect. I'm hoping this will solve the output problem, but now, I'm having my doubts.
I guess I'll just have wait and hope.
Thanks much, regards,