The smell as mentioned by Barry L.
The nearest I can come to describing it is, musty as if a room had be closed up for a very long time, but whilst from memory close, still not right.
I don't remember anyone giving an explaination as to why all TU104's had that smell and my only thoughts after all this time are probably fanciful.
As the Aircraft Spent a long time on the ground at home base they were deep cleaned and then sprayed with insectide and closed up.
After a very short while the 'scent' of the cleaning solutions and the spray permeated all those drapes, cloth covers, carpets , etc.
As the procedure was repeated at the end of each trip, the scent was replenished.
Probably a 'cr*p' theory.
I must admit that I envy Barry for having flown in them, although a combination of copious vodka and chicken would be a serious disincentive.
DIH