Alternatives to mounting tube sockets on a PCB
Rather strange question. How often you are changing tubes (unless you are making tube tester)? If 1-2 times per 2-3 year I wouldn't bother about the PCB strength.

But if you need stronger mount you can try:


Use thicker PCB (for example 2.5 or 3 mm thick).
Use better sockets - some has separate holes for PCB fixation, I've also seen an old fashion socket with thin brass tube in the center to be soldered on the PCB.
Mount sockets on the chassis of thin metal (steel or aluminum) and use wires from the bottom to connect to the PCB.
Don't use PCB at all.


Also - google how the vintage radios TVs looked inside (there are lot of pictures).

Hope this helps.