[BelowZero]

Thanks for the answers! I was thinking that it could have been to lower noise or hum as the R.F. and I.F. tubes are on one wire and most of the horz. and vert. tubes are on the other.

Here is the way they are dived in the 630TS,
X
R.F. Amp, Converter, R.F. Osc
1st Sound I.F., 2nd Sound I.F., 3rd Sound I.F., Sound Discr., 1st Audio
1st Pix I.F., 2nd Pix I.F, 3rd Pix I.F., 4th Pix I.F., Pix 2nd Det./D.C. Rest., 1st Video Amp, 2nd Video Amp, H. Sync. Discr.

Y
Audio Output,
1st Sync. Amp, Sync Separator, 2nd Sync. Amp/Hor. Disch., Vert Osc & Dischg., Vert. Output
H. Osc. Contr., Hor. Osc., Hor. Output, CRT.

Looking at early RCA schematics I see a couple of different designs,
On models 621TS, 721TS, 730TV1, the heaters are supplied by a single 6.3v winding but the CRT is fed by a separate 6.3 winding.

Models 630TS, 641TV, 8TS30, 8TV41, use the 12.6 CT.

Models 8T241, 8T270, 8TK29, 8TV321, 9T240 and up use a single 6.3v heater winding.