Validity of stamped H1B Visa after changing company?

Hi,

My H1B is processed by my current employer A and is valid till Sept 2016.I have not yet traveled to US.

Now I will be joining another company B. Is my stamped H1B visa is still valid?

Is there any visa related documents to be collected from employer A before leaving ?

Please let me know asap.

Your visa stamp will remain valid and usable unless consulate marks it as canceled in the passport.

If you have copy of 797 or original from A, then you are all set.