[Amps] Replacement of plate caps on glass tubes

[K6QD]

I have some old glass tubes where the plate cap bond to the glass envelope has become loose; i.e. the cap is being held on by the soldered wire going through the glass envelope to the internal plate.  The solder joint from the wire connection to the plate cap is intact and the tubes are good, but the bond to the glass has failed over time.  Can the caps be unsoldered, re-bonded and re-soldered?
Thanks for any help.  
de Mike, K6QD