Throat Vibrato

[Printen@xxxxxxxxxxxxxxxxxx (John Printen)]

Hello Fellow Harpists!
        I have just discovered this list server, and am slowly working
through the archives, however I thought I would throw out a question for
the seasoned players.  I have LOTS of questions, but I will try to pace
myself. 

Q: Are there any tricks, tips or exercises to help develop a good sounding
throat vibrato?
        I was listening to a Charlie Musselwhite track the other day, and
was really taken by the tone and warmth he has in his vibrato.  I've been
trying to devlop a decent sound, and have moved past the "machine gun"
sound we all used to make as kids, but it still sounds a little (a lot?)
thin.  Any tips would be appreciated!

Thanks,
John
Printen@xxxxxxxxxxxxxxxxxx