If you put Tung-Sol 5881s in you may never take them out.
For some reason they are night and day better than other 5881s in MOD 50 and IMO all other tube types as well. I tried EL34s but they didnt have the punch. The TS 5881s have everything. Theres lots of fans of them on this forum.
Not sure how they fair in MOD 100, but like I said, in the 50 they are almost untouchable IMO.