Thanks to all who have been following this thread and providing input.
UPDATE: What the problem was I can't say. What I can say is that after installing screen grid protection resistors on the output tubes, upgrading from KT88 to to KT120 output tubes and installing a Weber SS rectifier, all is wonderful. I also discovered my SP12 preamp came with a faulty 24 stepped volume control pot. That I replaced with a Blue Velvet volume pot. I can't beleive how good everything sounds and bias measurements are stable. This is what I expected when I purchased this gear but it took several months to work out the bugs. Probably not what Bob and his crew want to hear but such is my case. I have absolutely no regrets with my VTA stereo. It performs as it should now and I am loving it. I don't know what my problem was but I do beleive dcgillespie is on to something and really appreciate his guidance.
The ST-120 and SP-12, when working propery, rock!