Rectification with tube power supplies.
This is probably the most misunderstood part of a tube amplifier. It can be a mistake to simply copy something, just because it was presented as "very good". Cases where good design rules were not respected we find as well with companies of high reputation, as with any other company. Interestingly, we find less of such errors with DIY. Just to mention some of the most common errors: Adding 100's of microfarad as a first capacitor for 5U4G, too low DC resistance of transformer Raa winding, or draw excessive surge current from a rectifier tube during cold start. Caused by a low cost choke, which saturates at start up, or other causes. Combine this by not measuring peak current, and start up current. Just copy schematics, makes you copy the mistakes too. Just to give the classical warning once more, when you see more than 33uF on a 5U4G, or more than 4uF on a 274B tube, such a schematic is questionable. So this can already by seen from picture files. Wheras transformer Raa Resistance can be measured simple with a low cost multi meter. Yet while peak current is hard to measure, at least you should make a simulation, for instance with "PSU Designer", which is free to use for DIY. PSU Designer will work quickly and easy, and simulate peak current with Oscilloscope-like results, at any point of the circuit you select. For the hard core users there is LTSPICE freeware from Analog Devices. Though LTSPICE will take a very long time to understand when you are new to it.
Do not treat tube diodes like solid state diodes.
To give you some sensitivity for this item, take very good note of the following. When comparing tubes with solid state devices, the elementary difference is: With solid state devices it becomes difficult to build such for very high voltage. High current was never a problem. With tubes, it is reversed. It is difficult to build such for high current, and high voltage was never a problem. We have to realize, when stressing exactly this natural limit, the result will cause problems. So solid state diodes have less of a problem with repeating peak current, but they definitely have a reliability problem with exceeding the peak voltage. With tubes, the situation is reversed. Tubes have little problems when the peak voltage is exceeded occasionally, but they will develop problems quickly when the peak current is exceeded. So design considerations are totally another, and it would be completely wrong to use design considerations for solid state diodes for tube diodes as well, saying "a diode is a diode". The answer to this can only be: "a data sheet is a data sheet".
With solid state devices we all know, you can not abuse them with the peak voltage. If you do, catastrophic failure rate will rise sharply. As this is impossible to calculate with precision, good designers will measure it with in instrument, or alternatively over dimension the design ratings. This is in order to stay safely away from the damaging limits.
Even greater care should be taken with tubes, since these are devices with limited lifetime, and they are expensive. If you abuse them with peak current at start up, or exceed it during normal operation, lifetime will be shortened severely. We repeat the same as before: As this is impossible to calculate with precision, good designers will measure it with in instrument, or alternatively over dimension the design ratings. This is in order to stay safely away from the damaging limits.
Many good books have been written about tube power supplies, and of course we can not compress this in a few pages here. Keep three elementary things in mind, to get good tube lifetime: 1) Respect the maximum first capacitor value in the datasheet, and be aware when you use a maximum factor on the one end, you get a compromise on the other. 2) Understand and apply the derating curves, meaning at maximum current, you can not use the maximum voltage, and vice versa. 3) Use the MINIMUM copper resistance needed for a TUBE power supply transformer. Transformer building companies can not know what you need, so without specifications from your side, you get just "something". Which is only fine when you need "anything". This is so for solid state, but this is not so for tubes. You need to specify the copper resistance to them, and if they can't do the value the tube requires, you need to add the difference by using external resistors.
Summary: These rules above, need to be respected to get good tube life, and failure free operation. For maximum lifetime of any object, and sure for electron tubes, keep some distance from maximum limits. That is: maximum capacitor value, maximum voltage, maximum current, and minimum copper resistance.
Low residual hum. With a solid state power supply, the last final bit of hum can be eliminated by using larger capacitors. This is no problem for the diodes, as they do not suffer from transient current. With a tube power supply, the last final bit of hum, is not present because capacitors are too small, but because the choke is too small. Moreover, if circuits are not ideal you would be tempted to tweak components values, but better would be to use an improved circuit. The most commonly used circuit is Circuit #1, as below here, but this is the most unintelligent. In very many cases, simply use circuit #2 already brings an improvement. We call this "star grounding". Tough Circuit#2 is far from ideal, and Circuit #4 does the same even better and with less wiring. Circuit #3 shows one of those typical little things, you can observe when somebody does not treat a tube like a solid state diode. This makes sure the left side of the tube heater wire has the same current (and the same temperature by that) as the right side of the heater wire. Wheras Circuit #4 is such a logical and easy thing to do, but people do not understand why, and take Circuit #1, this is really painful. It is allowed to use Circuit #4, also if you do not understand why it is better, as it is free of patent rights. The words are: No ground loop risk, and electrical stray field. Circuit #5 is the ultimate circuit. Only possible with Lundahl chokes. This is the most beneficial circuit ever, for lowest hum. The choke is not only used here as an inductor, but also creates inductive decoupling of the complete rectifier parts from the amplifier circuit. There is no direct connection any more! All hum signals, no matter how they try to flow, must pass a choke now. Please also read the short explanations on the right, below here. After that I hope you understand why we say it is so silly to find Circuit #1 in most "professional" designs.