Audio Research VT100 MKIII Tube Replacement

I’m confused by the question
Are you trying to replace 6550 with 6H30? Or asking if there is a difference between the 6h30 and 6h30pi?

Fwiw all 6h30 tubes are the same.

You need to order the correct valves first, two sets of SIX. Not 12 singles or 6 pairs, or 3 sets or quads.. 

If the manufacture has options for different valves, they will be listed.
KT88, and 6550 usually can be interchanged.

No, they are not the same and certainly don't sound the same..

The small valves need to be balanced also..

Read then BUY, OP.. Save you a lot of money in the long run..

Have fun, be careful, and DON'T break off the index locator, pulling or swapping valves.. BE aware.. Be Careful..

Thank you for your fast response. Database of Audio Research says; VT100 MKIII: (4 matched pairs) 6550C power output, (4) 6H30 driver. I have ordered 4 matched pairs of 6550 tungsol however I am not sure about 6H30s. I wonder what are the difference between 6H30 and 6H30Pi.
Thanks !