B+ voltages

I've noticed that most high-gain amps have lower B+ for the initial stages, and higher B+ for later stages...what is the reason for this, and what tonal differences does it make? Is there a distinct disadvantage to giving all of your pre tubes the SAME B+?

Also, how do you know what voltage to give each stage? Is there some general guideline, or are there hard-and-fast rules that apply?

I'm guessing that the lower B+ in the preamp stages makes the preamp clip at a lower gain. Bear in mind that the term 'high gain' is quite abused, and generally it really just means 'lots of clipping'.

Many "two channel" tube amps are simply "added gain stage" amps; they drop in more gain stages to get distortion and these later stages typically get high B+ to allow for more clipping. Having high clipping high B+ gain stages earlier in the signal chain leads to the dreaded "blocking distortion" also known as "farting out"....not good

gain has to be dumped to avoid this usually with lower B+ (less gain) and or some filtering with resistors or caps in the signal path.

Some people like the low voltage distortion you get from a stage run at low B+, the Real McTube (my first DIY tube!) ran ~140VDC to the 12AX7 and sounded nice...