The rectifier I used depends on the power transformer you select. The higher voltage/higher cost one I used with 2 chokes, I used a 5V4G to drop the voltage some. Be aware of this when choosing a rectifier. I chose the 5V4G to drop 10V of DC over a 5AR4. The 5U4G will drop about 25V which will be too much drop unless you have a higher voltage transformer. Also it doesn't have the slow startup a 5AR4 or a 5V4G has.Bottom line is getting the plate voltage right around 400-405V on the EL34 and there are obviously different paths to get there. Here is a chart of rectifier voltage drops I came up with and PSUD2 software is great to sim a power supply.
The bom/web page has 2 different options for the power supply. But to answer your question, I wouldn't use a 5U4G.
The rectifier I used depends on the power transformer you select. The higher voltage/higher cost one I used with 2 chokes, I used a 5V4G to drop the voltage some. Be aware of this when choosing a rectifier. I chose the 5V4G to drop 10V of DC over a 5AR4. The 5U4G will drop about 25V which will be too much drop unless you have a higher voltage transformer. Also it doesn't have the slow startup a 5AR4 or a 5V4G has. Bottom line is getting the plate voltage right around 400-405V on the EL34 and there are obviously different paths to get there. Here is a chart of rectifier voltage drops I came up with and PSUD2 software is great to sim a power supply.