Here is my 2 cents on the subject.
The MWDR has a switch on the back for power supply tracking. It is labeled as "rectifier select" Note that each channel has a rectifier tracking switch. The up position is for silicon diode and the down position is for tube rectifier. The spongy is varaic power to reduce plate voltage and Bold is full power. That switch does not do anything to the rectifier tube. You must use the rectifier select switches to bypass the tube rectifiers.
Also, if you hear this hum through the speakers, it would be caused by voltage ripple in the power supply which could indicate that one of the rectifier tubes is off or weak. Two rectifier tubes are used at 100W and only one is used at 50W.
Yes, you can remove the Rectifier tubes if you have all of the rectifier select switches set to diode. Not sure how much the tube rectifiers contribute to the power supply when the diode is set since they always remain in the circuit and will be operating in parallel. The voltage drop across the silicon diodes will be far less than the voltage drop across the tube rectifier. The one rectifier tube does get bypassed in some ways with a relay when using 100W/50W switch on the front of the amp on each channel (when active the relay shorts out the 100k resistors on the plates to that additional rectifier tube is providing power with the other, when 50W power is set, the relay opens, and the rectifier plates do not conduct much with the 100k plate resistors in the circuit and then only one is contributing to the power source.
The power transformer does make noise, but you should not hear that though the speakers. Mark amps usually have a fan and that is what you hear which is usually louder than the power transformer noise. I have a few amps where you can turn off the fan, RA100 is one, with the fan off you can hear the transformer making similar noise like the MWDR. Roadster is no different. No fan.
You can experiment with the rectifier switches before you opt to remove the tube rectifiers. The Power transformer is on the same side of the amp as the Rectifier tubes. I doubt bypassing them with the switch or removing them will affect the PT noise. If you do hear the noise through the speakers, it is probably associated with any of the tubes in the amp, I would not rule out preamp tubes. If the noise is present but goes away when the rectifier select is set to diode, that would indicate the tube rectifiers are contributing to the noise. If that does not work, power down, let the tubes cool and remove the Rectifier tubes and try again. As I said above, the rectifier tubes are still operating in parallel to the silicon diodes, so if they are the source of noise, you have to remove them to determine it. Just do not change the state of the rectifier select when the Rectifiers are removed from the amp while power is applied. It is probably best to replace them and keep them in the amp at all times.
