[Penthode]

I once had a chance to see a 721. The first thing I noticed was there was no DC restoration. Secondly, the picture is slightly softer due to the narrower IF response (three IF stages instead of four). The number of tubes in the IF does not affect sensitivity as much as picture detail and the 721 has about 1 MHz less wide Video IF bandwidth than the 630.

It is interesting to note that the later intercarrier designs allowed set users on strong signal stations to adjust the fine tuning lower on the nyquist slope to improve picture detail and on weaker signal stations move it higher for better signal to noise performance at the expense of detail. The late 40's RCA sets were all split sound design which meant that the fine tuning was set for best sound, ignoring the picture. Hence a side-by-side close comparison will reveal the less expensive design of the 721.

But I would expect that most viewers would not be so critical and at about four feet from the face of the 10BP4 it would be hard to tell the difference in resolution. The DC component loss on the 721 is to me an issue however.