I've been told that the 6L6 driving the 6L6 is very hard on the xtal.
A lot of old designs were. Back then typical ham xtals were bigger and could take more current. When FT-243s appeared after WW2, they were considered tiny!
Thanks for the link, it's a pretty good design. The modified-Pierce circuit used in it is much easier on the crystal.
However, the rig could be improved in a few ways (IMHO):
1) Parasitic suppressor may be needed in the 6L6 plate lead. In some stubborn cases the grid lead may need one too.
2) There should be a 2.5 or 1 mH RFC across the output for safety.
3) The B+ switch should not be in the B+ lead. It should break the connection of the HV center-tap winding to ground.
4) A larger coil (physically, not inductance) in the pi-net is a good idea.
5) There should be a way to measure the 6L6 grid current during initial tune-up so that the drive can be set correctly.
6) A 5U4 can be substituted for the 5R4 in the power supply. Both will work but the 5U4 is more common.
73 de Jim, N2EY