why do B+1 and B+2 need to be above B+3 in the A1a?

[dms]

In regard to the A1a schematic, let's say I had a transformer that could supply a voltage high enough to hit my desired B+3,4,5 voltages, but could not supply the higher voltages at B+2 and B+1. Are the specific B+1 and B+2 voltages critical in relation to B+3?

I understand that B+3, 4, 5 have a big impact on sound (headroom?) as they feed the preamp/PI tubes, but I don't understand how important it is that B+2 and B+1 are even higher than B+3... Maybe they only need to be "somewhat" higher so that you have the room to drop them down over 2 stages of filtering to hit your desired B+3...

Can anyone explain in general why B+2 needs to be higher than B+3 and B+1 needs to be even higher?

Thanks for all attemps at explaining, Davids

[Elcabong]

B+2 needs to be lower than B+1 for proper tube operation. Then, both are higher than B+3 to allow room for amplifying the PI signal. I think it could work with lower voltages but you would get early distortion from the PA.