[Amps] Tube Identification

[George KB2Z]

Morning all,
I have a pair of Eimac 3-500 tubes I would like to sell and would 
like suggestions for identifying them.
They are putting out over a 1000W cw. I dont want to sell them to 
have an un-ethical person send back as bad, saying they are no good.
I sold a new tested pair of tubes a few years back and had that 
pulled on me. Once bitten, twice shy.
Thanks in advance, George KB2Z