These caps are usually wired in series for a total capacitance of 50 mfd (just right for a 5AR4 or 5U4 rectifier tube) and voltage capacity of 700V
We often stock 450V and may ship them at no extra cost.
100 mfd caps can be used to boost the overall bass response of any amp, but may need some knowledge
of power supplies before trying it (check out "Inside Tube Amps")