High voltage CT ( blue/red ) does go to ground.
the confusion is with the heater winding. both the 5V (yellow) and 6V (green) are CT. We do not need to use this but it can be done. the idea is with most rectifers the whole heater winding is at your high voltage. we need to tap off it to the rest of the power supply this can be done at one end or the middle (CT)

For our supply, just use the end and tape off the CT.

for example for a 5AR4, 5U4, 5R4, 5V3, 5V4, OR 5Y3 The heater in this case the 2 yellow go to pin 2 and 8 the high voltage (Blue 340VAC I think) go to pins 4 and 6 the high voltage CT ( blue/red ) to ground ( cap Neg) and we tap pin 8 for our high voltage to the choke we use pin 8 rather than 2 because if the above rectifers have a seprate cathode it is internaly connected to pin 8...John

That's for pointing out the CT. I thought that was going to be an easy question, but was more confused than ever.

I'm using a 6V4 as the rectifier and I hope the schematic below is correct. 1&7 are HV; 3 is choke tap; 4&5 are 5V heater.....Colin

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Let's stay a bit more conservative please for the first go 'round.
regards,
Douglas

In this case the CT just gets taped off and secured.

The 6CA4 has its heater isolated from the cathode and the CT is an 'extra' part. Again secure, and tape it off.
regards,
Dogulas

That would be the blue then
going to try to repost my pic as well...John