I usually tend to use 5U4GB’s as the rectifier when needing a high current tube rectifier and account for the larger voltage drop with the correct transformer however the 5AR4/GZ34 is a good tube as well. The 5AR4 and GZ34 is an indirectly heated cathode tube which means it takes longer to warm up. Long enough so the rest of the power tubes are also ready to draw some current. Why is this good? Well when running high voltages near the working voltage of your power supply capacitors this can help with the longevity of the caps. The 5U4 series heats up very quickly, often well before anything is drawing power. The result is that an unloaded power supply will exceed the working voltage of the capacitors until the rest of the tubes get hot. The 5AR4 (GZ34) rectifiers do not have this problem. Typical voltage drop for the 5AR4/GZ34 series is 17 volts where the 5U4GB can be up to 50. Also note the 5U4 series typically has a 3 Amp filament vs. the 5AR4/GZ34’s 1.9Amp.
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