I don't have a 78 but have the 77 that I find to have a better sound. I think the 77 is better soundwise than the 20b but the 20 is better than the 77. At the time I was looking for the 77, the 20 and the Fisher TFM1000 were also in the running but all the 20s around sor sale or available form Marantz were the 20b and the 77 was a tab better. The 20b is aboout on par with the 78 soundwise in terms of distance from the 77 though the 78 and 20b do not have the same sound. On a scale, the 20 to 77 had a sound advantage in favor of the 20 at about the same distance as the 78 to the 77. NONE of these are losers by any standard and I am talking about very minor differences in the advantages soundwise when these all were new. The 1 with the largest difference and the favorite actually was the TFM1000 but, they self-destructed every 6 months. I wish Fisher had gotten the reliability up there.
Today, I am not sure what the comparison result would show due to the change in station broadcast quality and the age of all of the units. I suspect that any unit not having been gone through will not meet original spec today and any unit that has been repaired or gone through will not have the same sound as when my testing was done since parts quality and sound associated with differeing parts could be sufficient enough to affect the unit. It is the 1 reason why there are those today who do not hear the differences between the 78 and 77 that was so evident when both were in production.
The biggest problem with the 20 series, like all of the Marantz o'scope units is finding a replacement for the scope and the fact ot the high voltage circuits in the tuner. Finding replacement scope tubes is difficult and getting very costly. It real advantage is if you have an antenna with a rotator and to see the quality of what in coming into the tuner. Way ahead of even a 3 meter setup (signal strength, center channel and multipath indicator) and for those guys who love bouncing meters or blue lights, way cooler.
The 20 will easly match and beat the 110 for pulling power. Never had a 20 up against my 110 Z series. When you get things up and running could you give us some comparitive feedback, please.