is there a way to tighten pins in tube sockets?

The hum and unstable bias just might be due to poor contacts on the pins. Bend them a little if you can, then get some contact cleaner and clean the pins and sockets. Put the tubes back in and you may not need to send these to VAC???

Get some socket savers. They come in 8 or 9 pin. Before you put them in just squeeze the female pins a tad and then stick the socket saver in so it fits tight. Now you will always replace your tubes in the socket saver not the sockets on your amp. I use them on my amps and they solve the problem.

+1 for the socket savers ONCE the pins are tightened. I got the ones from the tubemonger and I will say the sockets on the saver are real tight. I had a loose socket where the bias would drift and lost some pretty expensive tubes as a result before figuring that out. For me I had the sockets replaced first.

I was thinking there might be a "special tool" for performing the tighten operation. Since I work on BMW's, they have a "special tool" for everything. I'll take a look at the amp this weekend and see what's possible.