I just took possession of an Ampeg J-20 Jet and I have to say it's a tone lover's dream.

It came with metal covers on the preamp tubes. The hang tag's feature outline says "Padded steel tube cages prevent damage during transport."

My question is this: I can see that they can be removed. Should they be removed to promote heat dissipation? Should I have not played the amp with the tube covers on?

Anyone have experience with this?
It's up to you. Although my amp kept going from really quiet to ridiculously loud volumes on its own after I'd played it loud for anywhere over 20 minutes, I tried taking the preamp tube covers off and haven't had a problem since.
A dwarf might hear you. What then?

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^^ Thanks for the anecdote. I think that's good enough for me. I'm taking them off. I can only assume the covers could prevent heat dissipation and help the tubes overheat. Probably what happened to your amp. Good to know it hasn't troubled you since.
I'm sure that was just a coincidence. I've had my tube covers off and on with my 2205 and there was no difference. Do a little research and you will find there is nothing wrong with keeping the covers on. If you are worried about heat, get a small fan and set it behind your amp.
Heat dissapation is improved with them off, durability and security is improved with them on. *shrug. It's gravey to me; I leave them on, 'cause I'm lazy.