Indeed. The Modwright manual specifically mentions 6900 and 7119. Another source lists 7044 as a drop in for the 5687.
01-20-06: Cellorover
There is a list of recommended and non-recommended tubes in the Modwright owner's manual.
My question specifically requests users of tubes other than TungSol 5687 to describe the tonal characteristics of the tubes they have tried.
1markr, your comments have been insightful. Thank you.