You get an A+ for doing the homework assignment and posting diagrams.
Yes, solid-state diodes go in series with the tube rectifier sections. That way the solid-state takes all the PIV stress, not the tube which really can't do it well. Would not hurt to add some snubbers to the diodes to remove the Qrr. Here's Jim Hagerman's paper on that:
http://www.hagtech.com/pdf/snubber.pdf
Smart work on putting fuses on the tube's output to protect the
tube, not merely the
transformer, rather than have a tube fail from a short and then blow the secondary fuses. Spend a buck on fuses and never need to worry about losing a rectifier tube in a catastrophic way from overcurrent.
I suggest adding:
(1) A fuse to the secondary B+ center-tap because it has the current from both sides passing through it. That should cover all eventualities. Some people only fuse the center-tap but this doesn't take into account an alternate path for the B+ current through the heater circuit, if grounded, or through a wiring path.
(2) Fuses to the heater secondary, same arrangement—both legs and the center-tap—for the same reason: if a heater shorts it could conceivably cook the transformer. Heater fusing is tricky because of the massive current during startup, but the inrush limiter keeps that current down to the point that a fuse, likely a slo-blow, will work while it would not work in normal situation without a slo-blow that was drastically over-rated to withstand startup. But the inrush limiter makes it work.
The B+ fuses should not be 80 mA as that is at or above the 6X4's capacity. Figure out what the circuit is using. Probably few tens of mA. Your supply voltage is below 250 V so the fuse rating is honored? When the filter capacitors are empty the charging current can be quite high, but the fuse should tolerate this.
Don't forget to fuse the transformer
primary as well as the secondaries, in case something shorts in the transformer. This is to prevent relying upon your mains fuse/breaker as the safety device. Again, unlikely but this is how good design practices work.
You are still planning to add an inrush limiter for (a) heater secondary and (b) rectifier secondary, since cold-start is 5-10x normal current load. You will need to size this thermistor for the amount of current being drawn.
That will be a very protected supply and A+ work.
Another idea to consider as long as you're doing this work is to add a TRIAC to the power switch. This way the power switch, which is usually a hard to find component (hasn't been made in 60+ years), doesn't move any current, so the contacts forever last. An AK thread explains how to make this modification.
Again, good work on doing the homework and posting the diagram. More people should do this.