I stepped back for a few days from the rig to reevaluate the proceedings. The AVC does work but the negative bias is out of kilter on most tubes. Spent some time tracing out the bias circuit and all roads lead back to the SSB detector tube. I changed C95, the CW detector audio output coupler already and found out it is now toast. Checking around I found that the noise limiter output coupler cap C96 is out also. So it is good I guess that the C95 cap went out and made it easier to find what might have been a problem with the rig for a while now. Getting closer said the tortoise. I don't feel too bad as there is a well known AR OP who has some videos documenting his repairs on YouTube. He spent over 10 hours looking for the problem with his particular 75A-4 and has the videos to prove it. I did learn some good pointers from watching a few of the videos and will use his very good video when aligning up the 75A-4, once all repairs are completed.