[Amps] SB-200 Amp with 811 tubes?

[D Conklin]

Gurus,

Amp rookie here.

I got a SB-200 fitted with 2 811A tubes.   I was assuming that this was a plug-and-play replacement for the 572A.   A local ham who
has an extensive but not detailed memory indicates that this was a common mod due to 811 tubes being cheaper, but that it involved a
substantial amp mod and wasn't just a plug and play replacement.

I have searched the net for info on modding a SB-200 for 811 tubes and found nothing.  I also searched the QST index without luck.  I
need to know the mod so that i can check if the previous owner (SK) did it right, or if he completed it - this amp looks like it was
in the process of being refurbed at the time of his passing - maybe he was in the middle of converting it to or from 811s.

Any help greatly appreciated - you will go over my head pretty quickly on this stuff, so talk slowly    ;-) 

AI8P