A 5R4GYB is rated at 3100V PRV. You would need 3 1N4007's in series
in each leg (total of 6) to match the peak reverse voltage rating.

I have solid-stated the 5R4 in a Hallicrafters HT32B without
using a series resistor to drop the HV back down to that
produced by the 5R4. That's OK in this application,
because the 5R4 is only used for the plate supply for the 6146's.
Using the higher plate voltage, I just readjusted the grid bias
for the same 40 mA resting current.

73,
Ed K4PF