I have a 60w tube amp, would it be harmful to run vocals through it? It wouldn't need to be heard over a band, just as an announcement type of PA system for an auditorium/audience. Thanks.
It will make your vocals sound way better than a solid-state amp would. :-D

"Punk is not dead. Punk will only die when corporations can exploit and mass produce it."
Jello Biafra

(so is it dead?)
I don't think it would hurt it but I'd strongly recommend against it.

A guitar amp is made for amplifying a guitar of course. They are purposely designed to not have a flat frequency response.

Keyboard amps on the other hand usually do have the flat frequency response needed.

In short, guitar amp + vocals = bad
guitar amps have a natural midrange spike, which will make vocals sound bad. but try a keyboard or maybe a bass amp.
I'm not too concerned with sound (its just for talking at some informal event), I just want to make sure it won't hurt the amp at all. I've done it on a solid state amp, but not sure how tubes would handle it.
It will be fine if all you are using it for is "Will the owner of a green Tercel come to the front, your lights are on."
Quote by CodChick

Seriously, I'm not a fan of iphones and guitars mixing.