Is it normal for the woofer to move in/out slowly

Well, some Tube preamp manufactures recommend them turned on all the time, I've had mine on for over 2 years with original tubes...

1. It's not abnormal

2. It's only bad if it drives the woofers to their mechanical limits.

If you really wanted you could hang a scope on your speaker terminals and see what's happening.

1-1.5 volts peak is fine even for tweeters (That's what I get in the power amp connected directly to my main actively tri-amplified system's tweeters and they have over a thousand power cycles on them).

Bokfudo, My speakers does this. I have a tube pre which I turn off after listening, have done this for years with no issues. Back to your question, yes my speakers does this and I don't see it as a problem hence have not investigated. But I will not worry about it.

It sounds like it is OK since the woofers are not driven to their limit and they move slowly. I wish I could leave the tubed pre on all the time but like a light bulb, that would reduce the life of the tubes.

Thanks for the answers!

Here's a question I have concerning this. What would damage the tubes more, surge from turning pre-amp on and off repeatedly or leaving pre-amp on most of the time?