I've got an old Selmer 100 watt PA head that I'm using as a bass amp. Was originally EL34's but I've now converted it to take 6l6's. Selmer put an L-shaped piece of aluminium sheet behind the power valves in their amps .... no idea why, but if anyone can illuminate why, it would be much appreciated.

Problem is that as the 6l6 bottles are wider diameter, they rattle off the metal plate. I've "bent" it away as far as possible but at some bass frequencies it still rattles very loudly! Appart from just being very annoying, I'm worried that it will damage the valves. Can I simply remove it (the Output transformer is behind it) or if i do will will create some kind of weird output transformer valve induction coupling and blow up the planet?