why do pre..........

[SKATE RAT]

why do pre amp tubes have that metal cover?

[Psycho Bass Guy]

It's shielding against picking up noise. Tubes are wonderful voltage amplifiers, and their support structures can make for great antennas. Power and driver tubes don't need them because the signals they are dealing with are already stronger than most kinds of background noise could ever get.

[Highlander]

One rehearsal studio I regularly used in 78-79 was on a main road in West London, so there were a lot of taxi-cabs and police passing/based in the area - the Hiwatt used to pick-up radio broadcasts and was somewhat microphonic - we were stitched up by the owners and I noticed a nice shiny new Marshall sitting in our regular room had the same valve-set as mine - don't ask me how they got mixed up... Never had the problem again...

[OldManC]

I noticed a nice shiny new Marshall sitting in our regular room had the same valve-set as mine - don't ask me how they got mixed up... Never had the problem again...

There was a rehearsal studio in Burbank that had two or three small rooms and one huge room that was usually occupied by major acts rehearsing for albums or tours. My friend's band rehearsed there a lot and we saw all sorts of people come in and out of the place. Security was pretty much non-existent so Motley Crue lost a lot of pics and little crap like that... The Bangles, on the other hand, lost a whole case of cymbals that somehow ended up in the van of the drummer of my friend's band. He was pretty heavy handed even for a metalhead, and broke three or four of them before he gave up and just started selling them.

I, on the other hand, learned never to leave gear anywhere (lockout or not) that I didn't want to lose!