Audio Research REF3 tube question clarification

Audio Research REF3 kindly clarify.

Do the 5 Sovtek 6H30PI tubes have to be all matched to get the best sonic performance?

What do the 5 tubes actually control?

Hours on tubes, when should they be changed to get the BEST sonic performance as there seems to be different opinions.

Sovtek 5 tubes, some say change them up to 1600-1800 hours but other sugest 3000 hours, which is it?

Winged "C" (SED) 6550C tube, some say change up to 800 hours but others sugest 3000 hours, which is it?
thks for the info., thats even more hours.

My understanding is that 2 of 6H30PI tubes are per channel and the one left over is partial for power supply is this correct?

If 2 per channel would it not be important to have a matched pair for each channel?

Are there any differences between the 6H30PI tube sonically? for example the date made much of a difference sonically?

Difference between the ARC tubes or purchasing from a reputable tube dealer?
Tube life depends mainly on cathode current - the same tube used in different circuits can last for very different times.
Most tube preamplifiers work in class A, meaning that tube current is constant. Unless you have all data from your preamplifier you should rely on manufacturer advice.
The referred values for the 6550 (1500 hours) are typical for a power tube in an Audio Research amplifier operated at 65mA bias and do not apply to the Ref3 - my Ref3is now over 4300 hours and the 6550 still measures over 8500 micromhos.
I agree with microstrip. In an amp,the 6550 life expectancy is around 2000 hours plus or minus but, in the power supply of the Ref-3 it's coasting and will have a much longer lifespan. My ref 3 is at 6300 hours and sounds wonderful. A swap with a new 6550 made that point very clear. If you talk to the tube guys, the knowledgable ones, they'll agree.