RCA 630TS Transformer Question

[BelowZero]

Looking at the RCA 630TS power transformer wiring diagram I find that the 6.3 heater voltage is supplied by a center tapped 12.6 winding with one wire marked X and the other wire marked Y, with some tubes heaters fed by the X wire and other tubes including the CRT fed by Y.
scan0011.jpg

I'm working on a Fada 630TS clone chassis and the Sams schematic for that set shows the same 12.6 CT diagram as above. Some time in the past the power transformer has been replaced in this set, the replacement doesn't have the 12.6 CT winding, instead it has a 6.3 winding without a center tap, one wire grounded and the other wire feeding all of the 6.3 voltage to the tubes.
scan0012.jpg

The set was working with this replacement transformer but my question is would it be better to use a transformer with the 12.6 CT winding? I suppose the 6.3 winding in the replacement would be OK if the amp rating is high enough, Sams shows 5.1a for the 12.6.

I would like to learn what was the advantage of splitting a 12.6 winding to get the needed 6.3 heater voltage?

[Penthode]

There is no advantage having the center tapped 12.6 volt winding. A single 6.3 volt winding would have to supply about double the current of each of the split windings.

[Electronic M]

well in the RCA designs they do have an unusual B+ supply to achieve certain ends, and if the tubes were carefully divided between the two strings the ground tap could keep a heater cathode shorted tube from causing as bad of issues as with a single winding.....that is the only good reason I can think of for using the 12.6 CT aside from maybe parts cost.

[Don Lindsly]

During early TV design, engineers often incorporated circuits to remedy theoretical problems. As designs progressed, such unnecessary precautions were omitted to improve cost and reliability. The CT 12 volt filament was to minimize hum and reduce the wire size necessary to interconnect the tubes. Those tubes closest to the transformer would need wire gauge similar to the transformer winding. Once tube count was reduced, it was no longer a consideration.

The RCA 630 is an example of overkill.

[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.

[BelowZero]

The RCA 630 is an example of overkill.

I'm actually enjoying working on something that's over engineered than the other way around like most consumer electronics.