New 5F6A build, Low unloaded B+

[CascoSieg]

Newbie question, first build, apologies in advance if this is too basic a question.
I'm just starting a modified 5F6A and was fortunate to find a great deal on a MM P45RS PT and O45RS-L16 OT, so will be using those (see PT wiring diagram below). I'm starting to wire the heaters. For the rectifier, I'm planning to add safety diodes on the HT supply and a swtichable SS 2-phase option as well (as described by Rob Robinette) - see my power supply design below.
One unique thing about this PT is that the 5V secondary also has a 6.3V tap associated with the same common wire. Since it's more convenient, I'm using that 6.3 tap for the lamp, instead of one of the other heater taps.
I wired up just the rectifier socket through to the switch as designed and found I was only getting 388 VDC from a 5AR4 rectifier, and 319 VDC from the SS side. I also tried a 5R4-WGA, and that also produced 388 VDC. All I've read, as well as the PSUD power supply simulation I did indicates I should get something more like 460-470 VDC from the SS and 5AR4, and around 400 VDC from the 5R4.
Prior to installing the PT, I tested all leads and they produced the expected voltages. In place, the HT leads measure 350 VAC to ground each, and the heater measures 4.95 VAC.
I removed the tube and tested just the SS output: same result.
I removed all the diodes from the circuit, just to get back to a baseline, and retested using each tube: same result.
I removed the lamp/6.3 tap from the circuit and retested: same result.
Am I wrong to expect to see higher voltages at pin 8? (... and higher voltages from SS FW side?)
Does the rest of the filtering circuit need to be in place before the unloaded B+ can be established?
Does anything look wrong in the PS design?

Thanks very much!

[sluckey]

One unique thing about this PT is that the 5V secondary also has a 6.3V tap associated with the same common wire. Since it's more convenient, I'm using that 6.3 tap for the lamp, instead of one of the other heater taps.

I highly recommend you don't do that. There is high B+ voltage on that 6.3V tap!
 

I wired up just the rectifier socket through to the switch as designed and found I was only getting 388 VDC from a 5AR4 rectifier, and 319 VDC from the SS side. I also tried a 5R4-WGA, and that also produced 388 VDC. All I've read, as well as the PSUD power supply simulation I did indicates I should get something more like 460-470 VDC from the SS and 5AR4, and around 400 VDC from the 5R4.

I suspect the filter caps are not connected to the rectifier? If so, that's why the B+ is low. It will increase significantly when the filter caps are connected to the rectifier.

[CascoSieg]

Ah - yes, keeping high voltage away from the front panel makes sense.  Will remove the lamp from that circuit, and build the rest of the circuit, and re-test.
Thanks very much!

[pdf64]

Taking the bias feed from after that diode won’t work.

[ALBATROS1234]

As soon as I read the 1st sentence of the second paragraph I instantly thought , "you don't want to do that" but Sluckey beat me to it. Its kinda weird when your new to tube amps that there can exist ac and dc in the same wire simultaneously at two totally different voltage levels. When I learned that is when stuff started clicking and it started all to fall into place. In a tube you gotta pay attention to that . Its what coupling caps are for . They block that high voltage dc from going places that will cause damage. You generally don't think in these terms with low voltage solid state . Good luck its a fun hobby and very rewarding when you work for hours soldering and drilling holes etc then you plug your guitar in and it sounds better than you hoped for.

as for the low b+ maybe check that everything is grounded good especially filter caps.

[CascoSieg]

Much appreciated.
Updated my schema...