What I found interesting was the maximum current for P48 Phantom. Is it 2mA? Is it 10mA? Well, it was 2mA until 1979/1981, and then raised to 10mA.
The earliest Phantom mikes used the 48V as capsule bias. To get most of that to the capsule, their current drain had to be very low. 2mA flowing in 3.4K is 6.8V, 48V-6.8V= 41V, which is barely enough. Most such mikes really draw less than 1mA so they can put 45V on the capsule.
But 48V is awkwardly high, especially for battery. Mikes were developed to live on 24V and 12V. Down there you need a step-up converter (or an electret) to make bias voltage.
Also we started putting mikes closer to the band and further from the preamps. A mike might have to drive high levels into heavy capacitive loading. There should be several milliWatts of output power available.
So between bias converters and hot outputs, it seemed good to raise the permitted maximum current on P48 from 2mA to 10mA.
BTW: a dead-short on P48 will pass 48V/3K4= 14mA. So that is the maximum external load the 48V supply needs to deliver, and it need not stay at 48V simply not be damaged. (However in DIY we stick screwdrivers inside the box so we usually have to consider shorts on the top of the 2x6K8 resistors.)
